╭─────────────╮ │scroll to top│ ╰─────────────╯ ╭ serve_ssh_protocol.zig ───────────────────────────────────────╮ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ ╰───────────────────────────────────────────────────────────────╯
🬐 🬠 🬞🬂🬏 🬟 🬑 🬟 🬑 ╭861e7437..╮ 861e7437.. see-em: 🬋🬋🬋 🬋🬋🬋 🬋 🬋 │files │ commits refs discuss issues new login 🬐 🬠 🬐 🬠 🬑 🬟 🬰 ╰──────────╯ (102) user
╭────╮ ╭ clone ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ╮ │http│ ssh │ │ ╰────╯ ╰ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ╯
.. embed/ event/ test/ ui/ command.zig event.zig lib.zig main.zig main_wasm.zig serve.zig serve_ssh.zig ╭─────────────────────────────────╮ │serve_ssh_protocol.zig │ ╰─────────────────────────────────╯ test.zig testnet.zig try.zig ui.zig web.zig
791 792 fn runKex( 793 io: std.Io, 794 allocator: std.mem.Allocator, 795 reader: *std.Io.Reader, 796 writer: *std.Io.Writer, 797 host_key: *const HostKey, 798 client_version: []const u8, 799 ) !KexResult { 800 // exchange KEXINITs 801 const server_kex_init = try buildServerKexInit(io, allocator); 802 defer allocator.free(server_kex_init); 803 try writePlainPacket(io, writer, server_kex_init); 804 805 const client_kex_init = try readPlainPacket(allocator, reader); 806 defer allocator.free(client_kex_init); 807 808 var parsed = try parseClientKexInit(allocator, client_kex_init); 809 defer parsed.deinit(allocator); 810 811 if (!nameListContainsAny(parsed.kex_algos, &our_kex_algos)) return error.NoCommonKexAlgorithm; 812 if (!nameListContainsAny(parsed.host_key_algos, &our_host_key_algos)) return error.NoCommonHostKeyAlgorithm; 813 if (!nameListContainsAny(parsed.cs_cipher, &our_ciphers)) return error.NoCommonCipher; 814 if (!nameListContainsAny(parsed.sc_cipher, &our_ciphers)) return error.NoCommonCipher; 815 816 // receive KEX_ECDH_INIT — client's ephemeral curve25519 pubkey 817 const ecdh_init = try readPlainPacket(allocator, reader); 818 defer allocator.free(ecdh_init); 819 if (ecdh_init.len < 1 or ecdh_init[0] != SSH_MSG_KEX_ECDH_INIT) return error.UnexpectedMessage; 820 821 var ecdh_init_reader = std.Io.Reader.fixed(ecdh_init[1..]); 822 const client_ephemeral_alloc = try takeStringField(allocator, &ecdh_init_reader, X25519.public_length); 823 defer allocator.free(client_ephemeral_alloc); 824 if (client_ephemeral_alloc.len != X25519.public_length) return error.InvalidEphemeralKey; 825 var client_ephemeral: [X25519.public_length]u8 = undefined; 826 @memcpy(&client_ephemeral, client_ephemeral_alloc); 827 828 // our ephemeral keypair + shared secret 829 const server_ephemeral_kp = X25519.KeyPair.generate(io); 830 const shared_secret = try X25519.scalarmult(server_ephemeral_kp.secret_key, client_ephemeral); 831 832 // build host key blob (K_S) 833 var host_key_blob: std.ArrayList(u8) = .empty; 834 defer host_key_blob.deinit(allocator); 835 try host_key.appendPublicBlob(&host_key_blob, allocator); 836 837 // build exchange hash input and compute H 838 const exchange_hash = try computeExchangeHash( 839 allocator, 840 client_version, 841 server_version, 842 client_kex_init, 843 server_kex_init, 844 host_key_blob.items, 845 &client_ephemeral, 846 &server_ephemeral_kp.public_key, 847 &shared_secret, 848 ); 849 850 // sign H with the host key, format as ssh signature blob 851 var signature_blob: std.ArrayList(u8) = .empty; 852 defer signature_blob.deinit(allocator); 853 try host_key.appendSignatureBlob(&signature_blob, allocator, &exchange_hash); 854 855 // build & send KEX_ECDH_REPLY 856 var reply: std.ArrayList(u8) = .empty; 857 defer reply.deinit(allocator); 858 try reply.append(allocator, SSH_MSG_KEX_ECDH_REPLY); 859 try writeStringField(&reply, allocator, host_key_blob.items); 860 try writeStringField(&reply, allocator, &server_ephemeral_kp.public_key); 861 try writeStringField(&reply, allocator, signature_blob.items); 862 try writePlainPacket(io, writer, reply.items); 863 864 // NEWKEYS — both sides switch to encrypted mode after this is sent and 865 // the peer's NEWKEYS is received. 866 try writePlainPacket(io, writer, &[_]u8{SSH_MSG_NEWKEYS}); 867 868 const peer_newkeys = try readPlainPacket(allocator, reader); 869 defer allocator.free(peer_newkeys); 870 if (peer_newkeys.len < 1 or peer_newkeys[0] != SSH_MSG_NEWKEYS) return error.UnexpectedMessage; 871 872 // derive session keys per RFC 4253 §7.2. session_id == H for the first 873 // KEX. K is encoded as mpint in each derivation input. only the encrypt 874 // keys are needed for chacha20-poly1305 (no separate MAC/IV). 875 var keys: SessionKeys = undefined; 876 try deriveSessionKeys(allocator, &shared_secret, &exchange_hash, &exchange_hash, &keys); 877 878 return .{ 879 .cs_key = keys.cs_enc, 880 .sc_key = keys.sc_enc, 881 .session_id = exchange_hash, 882 }; 883 } 884 885 // --------------------------------------------------------------------------- 886 // exchange hash (RFC 4253 §8, RFC 5656 §4) 887 // --------------------------------------------------------------------------- 888 889 pub fn computeExchangeHash( 890 allocator: std.mem.Allocator, 891 client_version: []const u8, 892 server_version_str: []const u8, 893 client_kex_init: []const u8, 894 server_kex_init: []const u8, 895 host_key_blob: []const u8, 896 client_ephemeral: []const u8, 897 server_ephemeral: []const u8, 898 shared_secret: []const u8, 899 ) ![Sha256.digest_length]u8 { 900 var buf: std.ArrayList(u8) = .empty; 901 defer buf.deinit(allocator); 902 903 try writeStringField(&buf, allocator, client_version); 904 try writeStringField(&buf, allocator, server_version_str); 905 try writeStringField(&buf, allocator, client_kex_init); 906 try writeStringField(&buf, allocator, server_kex_init); 907 try writeStringField(&buf, allocator, host_key_blob); 908 try writeStringField(&buf, allocator, client_ephemeral); 909 try writeStringField(&buf, allocator, server_ephemeral); 910 try writeMpint(&buf, allocator, shared_secret); 911 912 var hasher = Sha256.init(.{}); 913 hasher.update(buf.items); 914 return hasher.finalResult(); 915 } 916 917 // --------------------------------------------------------------------------- 918 // key derivation (RFC 4253 §7.2) 919 // --------------------------------------------------------------------------- 920 921 // chacha20-poly1305@openssh.com wants 64 bytes per direction (32-byte main key 922 // + 32-byte header key); SHA256 produces 32, so each encrypt key is two hash 923 // blocks chained per RFC 4253. 924 pub const SessionKeys = struct { 925 cs_iv: [16]u8, 926 sc_iv: [16]u8, 927 cs_enc: [64]u8, 928 sc_enc: [64]u8, 929 }; 930 931 pub fn deriveSessionKeys( 932 allocator: std.mem.Allocator, 933 shared_secret: []const u8, 934 exchange_hash: []const u8, 935 session_id: []const u8, 936 out: *SessionKeys, 937 ) !void { 938 // pre-build the K || H prefix once; reused for every derivation 939 var prefix: std.ArrayList(u8) = .empty; 940 defer prefix.deinit(allocator); 941 try writeMpint(&prefix, allocator, shared_secret); 942 try prefix.appendSlice(allocator, exchange_hash); 943 944 try deriveKey(allocator, prefix.items, 'A', session_id, &out.cs_iv); 945 try deriveKey(allocator, prefix.items, 'B', session_id, &out.sc_iv); 946 try deriveKey(allocator, prefix.items, 'C', session_id, &out.cs_enc); 947 try deriveKey(allocator, prefix.items, 'D', session_id, &out.sc_enc); 948 } 949 950 fn deriveKey( 951 allocator: std.mem.Allocator, 952 prefix: []const u8, // K || H, already encoded 953 letter: u8, 954 session_id: []const u8, 955 out: []u8, 956 ) !void { 957 // first block: HASH(K || H || letter || session_id) 958 var first_block: [Sha256.digest_length]u8 = undefined; 959 { 960 var hasher = Sha256.init(.{}); 961 hasher.update(prefix); 962 hasher.update(&[_]u8{letter}); 963 hasher.update(session_id); 964 first_block = hasher.finalResult(); 965 } 966 const first_copy = @min(out.len, first_block.len); 967 @memcpy(out[0..first_copy], first_block[0..first_copy]); 968 969 // chain additional blocks if requested length exceeds one hash: 970 // K_{n+1} = HASH(K || H || K_1 || K_2 || … || K_n) 971 var chained: std.ArrayList(u8) = .empty; 972 defer chained.deinit(allocator); 973 try chained.appendSlice(allocator, first_block[0..]); 974 975 var produced: usize = first_copy; 976 while (produced < out.len) { 977 var hasher = Sha256.init(.{}); 978 hasher.update(prefix); 979 hasher.update(chained.items); 980 const block = hasher.finalResult(); 981 const copy_len = @min(out.len - produced, block.len); 982 @memcpy(out[produced .. produced + copy_len], block[0..copy_len]); 983 produced += copy_len; 984 try chained.appendSlice(allocator, block[0..]); 985 } 986 } 987 988 // --------------------------------------------------------------------------- 989 // chacha20-poly1305@openssh.com packet codec 990 // --------------------------------------------------------------------------- 991 // 992 // per openssh's PROTOCOL.chacha20poly1305: 993 // K_2 = first 32 bytes of key material — encrypts the packet body 994 // K_1 = next 32 bytes — encrypts the 4-byte length field 995 // nonce = 64-bit big-endian sequence number 996 // body = chacha20(K_2, nonce, counter=1) XOR plaintext_body 997 // length = chacha20(K_1, nonce, counter=0) XOR length_uint32_be 998 // mac = poly1305(poly_key, encrypted_length || encrypted_body) 999 // where poly_key = chacha20(K_2, nonce, counter=0)[0..32] 1000 // 1001 // padding is computed on the body alone (padding_length byte + payload + 1002 // padding) — the 4-byte length field is excluded from alignment. body must 1003 // be a multiple of 8 bytes; minimum padding 4 bytes. 1004 1005 pub const Cipher = struct { 1006 main_key: [32]u8, // K_2 1007 header_key: [32]u8, // K_1 1008 seq: u64, 1009 1010 pub fn init(key_material: *const [64]u8, initial_seq: u64) Cipher { 1011 return .{ 1012 .main_key = key_material[0..32].*, 1013 .header_key = key_material[32..64].*, 1014 .seq = initial_seq, 1015 }; 1016 } 1017 1018 fn makeNonce(seq: u64) [8]u8 { 1019 var nonce: [8]u8 = undefined; 1020 std.mem.writeInt(u64, &nonce, seq, .big); 1021 return nonce; 1022 } 1023 1024 pub fn writePacket( 1025 self: *Cipher, 1026 io: std.Io, 1027 allocator: std.mem.Allocator, 1028 writer: *std.Io.Writer, 1029 payload: []const u8, 1030 ) !void { 1031 const block: usize = 8; 1032 const initial_pad = block - ((1 + payload.len) % block); 1033 const padding_len: u8 = @intCast(if (initial_pad < 4) initial_pad + block else initial_pad); 1034 const body_len: u32 = @intCast(1 + payload.len + padding_len); 1035 1036 const nonce = makeNonce(self.seq); 1037 1038 // plaintext body = padding_length || payload || random padding 1039 const body = try allocator.alloc(u8, body_len); 1040 defer allocator.free(body); 1041 body[0] = padding_len; 1042 @memcpy(body[1 .. 1 + payload.len], payload); 1043 io.random(body[1 + payload.len ..]); 1044 1045 // encrypt body in place with counter=1 1046 ChaCha20.xor(body, body, 1, self.main_key, nonce); 1047 1048 // encrypt length field with header key, counter=0 1049 var enc_length: [4]u8 = undefined; 1050 var length_plain: [4]u8 = undefined; 1051 std.mem.writeInt(u32, &length_plain, body_len, .big); 1052 ChaCha20.xor(&enc_length, &length_plain, 0, self.header_key, nonce); 1053 1054 // poly1305 key = first 32 bytes of chacha20(K_2, nonce, counter=0) 1055 var poly_key: [Poly1305.key_length]u8 = undefined; 1056 ChaCha20.stream(&poly_key, 0, self.main_key, nonce); 1057 1058 // mac over encrypted_length || encrypted_body 1059 const mac_input = try allocator.alloc(u8, 4 + body_len); 1060 defer allocator.free(mac_input); 1061 @memcpy(mac_input[0..4], &enc_length); 1062 @memcpy(mac_input[4..], body); 1063 var tag: [Poly1305.mac_length]u8 = undefined; 1064 Poly1305.create(&tag, mac_input, &poly_key); 1065 1066 try writer.writeAll(&enc_length); 1067 try writer.writeAll(body); 1068 try writer.writeAll(&tag); 1069 try writer.flush(); 1070 1071 self.seq += 1; 1072 } 1073 1074 pub fn readPacket( 1075 self: *Cipher, 1076 allocator: std.mem.Allocator, 1077 reader: *std.Io.Reader, 1078 ) ![]u8 { 1079 const nonce = makeNonce(self.seq); 1080 1081 var enc_length: [4]u8 = undefined; 1082 try reader.readSliceAll(&enc_length); 1083 1084 var length_plain: [4]u8 = undefined; 1085 ChaCha20.xor(&length_plain, &enc_length, 0, self.header_key, nonce); 1086 const body_len = std.mem.readInt(u32, &length_plain, .big); 1087 if (body_len < 8 or body_len > max_packet_len or body_len % 8 != 0) return error.InvalidPacketLength; 1088 1089 const enc_body = try allocator.alloc(u8, body_len); 1090 defer allocator.free(enc_body); 1091 try reader.readSliceAll(enc_body); 1092 1093 var tag_recv: [Poly1305.mac_length]u8 = undefined; 1094 try reader.readSliceAll(&tag_recv); 1095 1096 var poly_key: [Poly1305.key_length]u8 = undefined; 1097 ChaCha20.stream(&poly_key, 0, self.main_key, nonce); 1098 1099 const mac_input = try allocator.alloc(u8, 4 + body_len); 1100 defer allocator.free(mac_input); 1101 @memcpy(mac_input[0..4], &enc_length); 1102 @memcpy(mac_input[4..], enc_body); 1103 var tag_computed: [Poly1305.mac_length]u8 = undefined; 1104 Poly1305.create(&tag_computed, mac_input, &poly_key); 1105 if (!std.crypto.timing_safe.eql([Poly1305.mac_length]u8, tag_recv, tag_computed)) { 1106 return error.MacVerificationFailed; 1107 } 1108 1109 // decrypt body in place into a separate buffer (caller owns) 1110 const body = try allocator.alloc(u8, body_len); 1111 errdefer allocator.free(body); 1112 ChaCha20.xor(body, enc_body, 1, self.main_key, nonce); 1113 1114 const padding_len = body[0]; 1115 if (padding_len < 4 or 1 + @as(u32, padding_len) > body_len) return error.InvalidPadding; 1116 const payload_len = body_len - 1 - @as(u32, padding_len); 1117 1118 const payload = try allocator.dupe(u8, body[1 .. 1 + payload_len]); 1119 allocator.free(body); 1120 1121 self.seq += 1; 1122 return payload; 1123 } 1124 }; 1125 1126 // --------------------------------------------------------------------------- 1127 // post-KEX: service request + user authentication (RFC 4252) 1128 // --------------------------------------------------------------------------- 1129 1130 /// "SHA256:" (7 bytes) + base64-no-padding of a 32-byte SHA256 digest 1131 /// (43 bytes) = 50 bytes. matches what openssh's client logs as 1132 /// `Offering public key: … SHA256:…`. 1133 pub const fingerprint_len = 50; 1134 1135 /// hash the SSH wire-format pubkey blob (`string algo` + `string raw_key`) 1136 /// the same way openssh does for `ssh-keygen -lf` / authorized-key logs. 1137 pub fn formatFingerprint(pubkey_blob: []const u8) [fingerprint_len]u8 { 1138 var digest: [Sha256.digest_length]u8 = undefined; 1139 Sha256.hash(pubkey_blob, &digest, .{}); 1140 1141 var out: [fingerprint_len]u8 = undefined; 1142 @memcpy(out[0..7], "SHA256:"); 1143 const encoded = std.base64.standard_no_pad.Encoder.encode(out[7..], &digest); 1144 std.debug.assert(encoded.len == fingerprint_len - 7); 1145 return out; 1146 } 1147 1148 fn runAuth( 1149 io: std.Io, 1150 allocator: std.mem.Allocator, 1151 reader: *std.Io.Reader, 1152 writer: *std.Io.Writer, 1153 cs_cipher: *Cipher, 1154 sc_cipher: *Cipher, 1155 session_id: *const [Sha256.digest_length]u8, 1156 ) ![fingerprint_len]u8 { 1157 // step 1: service request for ssh-userauth → service accept 1158 { 1159 const req = try cs_cipher.readPacket(allocator, reader); 1160 defer allocator.free(req); 1161 if (req.len >= 1 and req[0] == SSH_MSG_KEXINIT) { 1162 try sendDisconnect(io, allocator, sc_cipher, writer, "rekey is not supported"); 1163 return error.RekeyUnsupported; 1164 } 1165 if (req.len < 1 or req[0] != SSH_MSG_SERVICE_REQUEST) return error.UnexpectedMessage; 1166 1167 var req_reader = std.Io.Reader.fixed(req[1..]); 1168 const service = try takeStringField(allocator, &req_reader, 64); 1169 defer allocator.free(service); 1170 if (!std.mem.eql(u8, service, "ssh-userauth")) return error.UnsupportedService; 1171 1172 var accept: std.ArrayList(u8) = .empty; 1173 defer accept.deinit(allocator); 1174 try accept.append(allocator, SSH_MSG_SERVICE_ACCEPT); 1175 try writeStringField(&accept, allocator, "ssh-userauth"); 1176 try sc_cipher.writePacket(io, allocator, writer, accept.items); 1177 } 1178 1179 // step 2: USERAUTH loop until SUCCESS. accept any ed25519 key whose 1180 // signature verifies against the offered pubkey. 1181 var auth_attempts: u32 = 0; 1182 while (true) { 1183 const req = try cs_cipher.readPacket(allocator, reader); 1184 defer allocator.free(req); 1185 if (req.len >= 1 and req[0] == SSH_MSG_KEXINIT) { 1186 try sendDisconnect(io, allocator, sc_cipher, writer, "rekey is not supported"); 1187 return error.RekeyUnsupported; 1188 } 1189 if (req.len < 1 or req[0] != SSH_MSG_USERAUTH_REQUEST) return error.UnexpectedMessage; 1190 1191 var req_reader = std.Io.Reader.fixed(req[1..]); 1192 const user_name = try takeStringField(allocator, &req_reader, 256); 1193 defer allocator.free(user_name); 1194 const service_name = try takeStringField(allocator, &req_reader, 64); 1195 defer allocator.free(service_name); 1196 const method = try takeStringField(allocator, &req_reader, 64); 1197 defer allocator.free(method); 1198 1199 if (!std.mem.eql(u8, method, "publickey")) { 1200 auth_attempts += 1; 1201 if (auth_attempts >= max_auth_attempts) return error.TooManyAuthAttempts; 1202 try sendUserauthFailure(io, allocator, sc_cipher, writer); 1203 continue; 1204 } 1205 1206 const has_signature = (try req_reader.takeByte()) != 0; 1207 const algo = try takeStringField(allocator, &req_reader, 64); 1208 defer allocator.free(algo); 1209 const pubkey_blob = try takeStringField(allocator, &req_reader, 4096); 1210 defer allocator.free(pubkey_blob); 1211 1212 if (!std.mem.eql(u8, algo, "ssh-ed25519")) { 1213 auth_attempts += 1; 1214 if (auth_attempts >= max_auth_attempts) return error.TooManyAuthAttempts; 1215 try sendUserauthFailure(io, allocator, sc_cipher, writer); 1216 continue; 1217 } 1218 1219 if (!has_signature) { 1220 // probe — tell the client this key is acceptable so it'll send 1221 // the signed version next. 1222 var pk_ok: std.ArrayList(u8) = .empty; 1223 defer pk_ok.deinit(allocator); 1224 try pk_ok.append(allocator, SSH_MSG_USERAUTH_PK_OK); 1225 try writeStringField(&pk_ok, allocator, algo); 1226 try writeStringField(&pk_ok, allocator, pubkey_blob); 1227 try sc_cipher.writePacket(io, allocator, writer, pk_ok.items); 1228 continue; 1229 } 1230 1231 // has signature — verify it 1232 const signature_blob = try takeStringField(allocator, &req_reader, 1024); 1233 defer allocator.free(signature_blob); 1234 1235 const ok = verifyUserauthSignature( 1236 allocator, 1237 session_id, 1238 user_name, 1239 service_name, 1240 algo, 1241 pubkey_blob, 1242 signature_blob, 1243 ) catch false; 1244 1245 if (!ok) { 1246 auth_attempts += 1; 1247 if (auth_attempts >= max_auth_attempts) return error.TooManyAuthAttempts; 1248 try sendUserauthFailure(io, allocator, sc_cipher, writer); 1249 continue; 1250 } 1251 1252 try sc_cipher.writePacket(io, allocator, writer, &[_]u8{SSH_MSG_USERAUTH_SUCCESS}); 1253 return formatFingerprint(pubkey_blob); 1254 } 1255 } 1256 1257 fn sendUserauthFailure( 1258 io: std.Io, 1259 allocator: std.mem.Allocator, 1260 sc_cipher: *Cipher, 1261 writer: *std.Io.Writer, 1262 ) !void { 1263 var buf: std.ArrayList(u8) = .empty; 1264 defer buf.deinit(allocator); 1265 try buf.append(allocator, SSH_MSG_USERAUTH_FAILURE); 1266 try writeNameList(&buf, allocator, &.{"publickey"}); // allowed methods 1267 try buf.append(allocator, 0); // partial_success = false 1268 try sc_cipher.writePacket(io, allocator, writer, buf.items); 1269 } 1270 1271 fn sendDisconnect( 1272 io: std.Io, 1273 allocator: std.mem.Allocator, 1274 sc_cipher: *Cipher, 1275 writer: *std.Io.Writer, 1276 description: []const u8, 1277 ) !void { 1278 var buf: std.ArrayList(u8) = .empty; 1279 defer buf.deinit(allocator); 1280 try buf.append(allocator, SSH_MSG_DISCONNECT); 1281 try writeU32(&buf, allocator, SSH_DISCONNECT_PROTOCOL_ERROR); 1282 try writeStringField(&buf, allocator, description); 1283 try writeStringField(&buf, allocator, ""); 1284 try sc_cipher.writePacket(io, allocator, writer, buf.items); 1285 } 1286 1287 /// Append the canonical publickey-signed-data bytes (RFC 4252 §7) to `buf`. 1288 /// Used by the server to recompute the signed input for verification 1289 pub fn appendPublickeySignedData( 1290 buf: *std.ArrayList(u8), 1291 allocator: std.mem.Allocator, 1292 session_id: []const u8, 1293 user_name: []const u8, 1294 service_name: []const u8, 1295 algo: []const u8, 1296 pubkey_blob: []const u8, 1297 ) !void { 1298 try writeStringField(buf, allocator, session_id); 1299 try buf.append(allocator, SSH_MSG_USERAUTH_REQUEST); 1300 try writeStringField(buf, allocator, user_name); 1301 try writeStringField(buf, allocator, service_name); 1302 try writeStringField(buf, allocator, "publickey"); 1303 try buf.append(allocator, 1); 1304 try writeStringField(buf, allocator, algo); 1305 try writeStringField(buf, allocator, pubkey_blob); 1306 } 1307 1308 // build the bytes a publickey signature is computed over (RFC 4252 §7) and 1309 // verify the supplied signature against them. 1310 fn verifyUserauthSignature( 1311 allocator: std.mem.Allocator, 1312 session_id: *const [Sha256.digest_length]u8, 1313 user_name: []const u8, 1314 service_name: []const u8, 1315 algo: []const u8, 1316 pubkey_blob: []const u8, 1317 signature_blob: []const u8, 1318 ) !bool { 1319 var signed: std.ArrayList(u8) = .empty; 1320 defer signed.deinit(allocator); 1321 try appendPublickeySignedData(&signed, allocator, session_id, user_name, service_name, algo, pubkey_blob); 1322 1323 // parse pubkey_blob: string "ssh-ed25519" || string raw_pubkey 1324 var pubkey_reader = std.Io.Reader.fixed(pubkey_blob); 1325 const pk_algo = try takeStringField(allocator, &pubkey_reader, 64); 1326 defer allocator.free(pk_algo); 1327 if (!std.mem.eql(u8, pk_algo, "ssh-ed25519")) return false; 1328 const raw_pubkey = try takeStringField(allocator, &pubkey_reader, 64); 1329 defer allocator.free(raw_pubkey); 1330 if (raw_pubkey.len != Ed25519.PublicKey.encoded_length) return false; 1331 1332 // parse signature_blob: string "ssh-ed25519" || string raw_signature 1333 var sig_reader = std.Io.Reader.fixed(signature_blob); 1334 const sig_algo = try takeStringField(allocator, &sig_reader, 64); 1335 defer allocator.free(sig_algo); 1336 if (!std.mem.eql(u8, sig_algo, "ssh-ed25519")) return false; 1337 const raw_sig = try takeStringField(allocator, &sig_reader, Ed25519.Signature.encoded_length); 1338 defer allocator.free(raw_sig); 1339 if (raw_sig.len != Ed25519.Signature.encoded_length) return false; 1340 1341 var pubkey_bytes: [Ed25519.PublicKey.encoded_length]u8 = undefined; 1342 @memcpy(&pubkey_bytes, raw_pubkey); 1343 var sig_bytes: [Ed25519.Signature.encoded_length]u8 = undefined; 1344 @memcpy(&sig_bytes, raw_sig); 1345 1346 const pk = Ed25519.PublicKey.fromBytes(pubkey_bytes) catch return false; 1347 const sig = Ed25519.Signature.fromBytes(sig_bytes); 1348 sig.verify(signed.items, pk) catch return false; 1349 return true; 1350 } 1351 1352 // --------------------------------------------------------------------------- 1353 // connection layer (RFC 4254): channels, requests, data, flow control 1354 // --------------------------------------------------------------------------- 1355 1356 const Channel = struct { 1357 local_id: u32, 1358 remote_id: u32, 1359 local_window: u32, // bytes peer may still send us before we adjust 1360 remote_window: u32, // bytes we may still send to peer before they adjust 1361 max_packet: u32, // max CHANNEL_DATA payload the peer accepts in one packet 1362 eof_received: bool = false, 1363 pty: ?PtySize = null, 1364 }; 1365 1366 pub const PtySize = struct { width_cells: u16, height_cells: u16 }; 1367 1368 fn runChannelLayer( 1369 io: std.Io, 1370 allocator: std.mem.Allocator, 1371 reader: *std.Io.Reader, 1372 writer: *std.Io.Writer, 1373 cs_cipher: *Cipher, 1374 sc_cipher: *Cipher, 1375 fingerprint: *const [fingerprint_len]u8, 1376 handler: anytype, 1377 ) !void { 1378 var channel: ?Channel = null; 1379 var pending_exec: ?[]u8 = null; 1380 defer if (pending_exec) |s| allocator.free(s); 1381 1382 while (true) { 1383 const packet = try cs_cipher.readPacket(allocator, reader); 1384 defer allocator.free(packet); 1385 if (packet.len < 1) return error.EmptyPacket; 1386 const msg_type = packet[0]; 1387 1388 switch (msg_type) { 1389 SSH_MSG_GLOBAL_REQUEST => try handleGlobalRequest(io, allocator, sc_cipher, writer, packet), 1390 1391 SSH_MSG_KEXINIT => { 1392 try sendDisconnect(io, allocator, sc_cipher, writer, "rekey is not supported"); 1393 return error.RekeyUnsupported; 1394 }, 1395 1396 SSH_MSG_CHANNEL_OPEN => { 1397 if (channel != null) { 1398 try sendChannelOpenFailure(io, allocator, sc_cipher, writer, packet, SSH_OPEN_RESOURCE_SHORTAGE, "only one channel per connection"); 1399 continue; 1400 } 1401 channel = try handleChannelOpen(io, allocator, sc_cipher, writer, packet) orelse continue; 1402 }, 1403 1404 SSH_MSG_CHANNEL_REQUEST => { 1405 const ch = if (channel) |*c| c else continue; 1406 const start_request = try handleChannelRequest(io, allocator, sc_cipher, writer, ch, packet, &pending_exec); 1407 if (start_request) |req_kind| { 1408 const request: Request = switch (req_kind) { 1409 .shell => .{ .shell = ch.pty }, 1410 .exec => .{ .exec = pending_exec.? }, 1411 }; 1412 var sess = SessionCtx{ 1413 .io = io, 1414 .allocator = allocator, 1415 .reader = reader, 1416 .writer = writer, 1417 .cs_cipher = cs_cipher, 1418 .sc_cipher = sc_cipher, 1419 .channel = ch, 1420 .fingerprint = fingerprint.*, 1421 }; 1422 defer sess.deinit(); 1423 handler.handleSession(&sess, request) catch |session_err| { 1424 // try to send a non-zero exit status before closing 1425 sess.exit(1) catch {}; 1426 return session_err; 1427 }; 1428 if (!sess.closed) try sess.exit(0); 1429 return; 1430 } 1431 }, 1432 1433 SSH_MSG_CHANNEL_WINDOW_ADJUST => { 1434 const ch = if (channel) |*c| c else continue; 1435 try handleWindowAdjust(ch, packet); 1436 }, 1437 1438 SSH_MSG_CHANNEL_DATA, SSH_MSG_CHANNEL_EXTENDED_DATA => { 1439 const ch = if (channel) |*c| c else continue; 1440 // before shell/exec the client shouldn't be sending data, but 1441 // some clients are chatty; discard and refill window. 1442 try discardChannelData(io, allocator, sc_cipher, writer, ch, packet, msg_type == SSH_MSG_CHANNEL_EXTENDED_DATA); 1443 }, 1444 1445 SSH_MSG_CHANNEL_EOF => { 1446 if (channel) |*c| { 1447 try parseChannelId(packet, c.local_id); 1448 c.eof_received = true; 1449 } 1450 }, 1451 1452 SSH_MSG_CHANNEL_CLOSE => { 1453 if (channel) |*c| try parseChannelId(packet, c.local_id); 1454 return; 1455 }, 1456 1457 else => {}, // ignore unknown messages 1458 } 1459 } 1460 } 1461 1462 fn handleGlobalRequest( 1463 io: std.Io, 1464 allocator: std.mem.Allocator, 1465 sc_cipher: *Cipher, 1466 writer: *std.Io.Writer, 1467 packet: []const u8, 1468 ) !void { 1469 // byte SSH_MSG_GLOBAL_REQUEST 1470 // string request_name 1471 // boolean want_reply 1472 // …request-specific data we ignore 1473 var r = std.Io.Reader.fixed(packet[1..]); 1474 const name = try takeStringField(allocator, &r, 256); 1475 defer allocator.free(name); 1476 const want_reply = (try r.takeByte()) != 0; 1477 if (want_reply) { 1478 try sc_cipher.writePacket(io, allocator, writer, &[_]u8{SSH_MSG_REQUEST_FAILURE}); 1479 } 1480 } 1481 1482 /// Parse a CHANNEL_OPEN. On a session channel, send CHANNEL_OPEN_CONFIRMATION 1483 /// and return the new Channel. On other types, send CHANNEL_OPEN_FAILURE and 1484 /// return null. 1485 fn handleChannelOpen( 1486 io: std.Io, 1487 allocator: std.mem.Allocator, 1488 sc_cipher: *Cipher, 1489 writer: *std.Io.Writer, 1490 packet: []const u8, 1491 ) !?Channel { 1492 // byte SSH_MSG_CHANNEL_OPEN 1493 // string channel_type 1494 // uint32 sender_channel (peer's id) 1495 // uint32 initial_window 1496 // uint32 max_packet 1497 var r = std.Io.Reader.fixed(packet[1..]); 1498 const ch_type = try takeStringField(allocator, &r, 64); 1499 defer allocator.free(ch_type); 1500 const remote_id = try r.takeInt(u32, .big); 1501 const initial_window = try r.takeInt(u32, .big); 1502 const max_packet = try r.takeInt(u32, .big); 1503 1504 if (!std.mem.eql(u8, ch_type, "session")) { 1505 try sendChannelOpenFailure(io, allocator, sc_cipher, writer, packet, SSH_OPEN_UNKNOWN_CHANNEL_TYPE, "only session channels are supported"); 1506 return null; 1507 } 1508 1509 const local_id: u32 = 0; // single-channel connection — id is always 0 from our side 1510 var reply: std.ArrayList(u8) = .empty; 1511 defer reply.deinit(allocator); 1512 try reply.append(allocator, SSH_MSG_CHANNEL_OPEN_CONFIRMATION); 1513 try writeU32(&reply, allocator, remote_id); 1514 try writeU32(&reply, allocator, local_id); 1515 try writeU32(&reply, allocator, initial_recv_window); 1516 try writeU32(&reply, allocator, max_packet_size); 1517 try sc_cipher.writePacket(io, allocator, writer, reply.items); 1518 1519 return .{ 1520 .local_id = local_id, 1521 .remote_id = remote_id, 1522 .local_window = initial_recv_window, 1523 .remote_window = initial_window, 1524 .max_packet = max_packet, 1525 }; 1526 } 1527 1528 fn sendChannelOpenFailure( 1529 io: std.Io, 1530 allocator: std.mem.Allocator, 1531 sc_cipher: *Cipher, 1532 writer: *std.Io.Writer, 1533 open_packet: []const u8, 1534 reason: u32, 1535 description: []const u8, 1536 ) !void { 1537 // recover the sender_channel field from the CHANNEL_OPEN packet so we 1538 // address the failure to the correct id 1539 var r = std.Io.Reader.fixed(open_packet[1..]); 1540 const ch_type_len = try r.takeInt(u32, .big); 1541 try r.discardAll(ch_type_len); 1542 const remote_id = try r.takeInt(u32, .big); 1543 1544 var reply: std.ArrayList(u8) = .empty; 1545 defer reply.deinit(allocator); 1546 try reply.append(allocator, SSH_MSG_CHANNEL_OPEN_FAILURE); 1547 try writeU32(&reply, allocator, remote_id); 1548 try writeU32(&reply, allocator, reason); 1549 try writeStringField(&reply, allocator, description); 1550 try writeStringField(&reply, allocator, ""); // language tag 1551 try sc_cipher.writePacket(io, allocator, writer, reply.items); 1552 } 1553 1554 const RequestKind = enum { shell, exec }; 1555 1556 /// Returns the kind of session request if this triggered one, else null. 1557 fn handleChannelRequest( 1558 io: std.Io, 1559 allocator: std.mem.Allocator, 1560 sc_cipher: *Cipher, 1561 writer: *std.Io.Writer, 1562 ch: *Channel, 1563 packet: []const u8, 1564 pending_exec: *?[]u8, 1565 ) !?RequestKind { 1566 // byte SSH_MSG_CHANNEL_REQUEST 1567 // uint32 recipient_channel (== our local_id) 1568 // string request_type 1569 // boolean want_reply 1570 // …request-specific data 1571 var r = std.Io.Reader.fixed(packet[1..]); 1572 const recipient_channel = try r.takeInt(u32, .big); 1573 if (recipient_channel != ch.local_id) return error.UnknownChannel; 1574 const req_type = try takeStringField(allocator, &r, 64); 1575 defer allocator.free(req_type); 1576 const want_reply = (try r.takeByte()) != 0; 1577 1578 if (std.mem.eql(u8, req_type, "pty-req")) { 1579 // string TERM, uint32 width chars, uint32 height rows, uint32 width px, 1580 // uint32 height px, string modes 1581 const term = try takeStringField(allocator, &r, 64); 1582 defer allocator.free(term); 1583 const width = try r.takeInt(u32, .big); 1584 const height = try r.takeInt(u32, .big); 1585 ch.pty = .{ .width_cells = @intCast(@min(width, 0xFFFF)), .height_cells = @intCast(@min(height, 0xFFFF)) }; 1586 try replyChannelRequest(io, allocator, sc_cipher, writer, ch, want_reply, true); 1587 return null; 1588 } 1589 1590 if (std.mem.eql(u8, req_type, "env")) { 1591 // ignore environment variables silently (we don't pass them anywhere) 1592 try replyChannelRequest(io, allocator, sc_cipher, writer, ch, want_reply, true); 1593 return null; 1594 } 1595 1596 if (std.mem.eql(u8, req_type, "window-change")) { 1597 // uint32 width cells, uint32 height rows, uint32 width px, uint32 height px 1598 const width = try r.takeInt(u32, .big); 1599 const height = try r.takeInt(u32, .big); 1600 if (ch.pty != null) { 1601 ch.pty = .{ .width_cells = @intCast(@min(width, 0xFFFF)), .height_cells = @intCast(@min(height, 0xFFFF)) }; 1602 } 1603 // spec: window-change MUST NOT request a reply, but accept either 1604 try replyChannelRequest(io, allocator, sc_cipher, writer, ch, want_reply, true); 1605 return null; 1606 } 1607 1608 if (std.mem.eql(u8, req_type, "shell")) { 1609 try replyChannelRequest(io, allocator, sc_cipher, writer, ch, want_reply, true); 1610 return .shell; 1611 } 1612 1613 if (std.mem.eql(u8, req_type, "exec")) { 1614 // capture the command string for the handler to inspect 1615 const cmd = try takeStringField(allocator, &r, 4096); 1616 if (pending_exec.*) |old| allocator.free(old); 1617 pending_exec.* = cmd; 1618 try replyChannelRequest(io, allocator, sc_cipher, writer, ch, want_reply, true); 1619 return .exec; 1620 } 1621 1622 // unknown request kind — fail it 1623 try replyChannelRequest(io, allocator, sc_cipher, writer, ch, want_reply, false); 1624 return null; 1625 } 1626 1627 fn replyChannelRequest( 1628 io: std.Io, 1629 allocator: std.mem.Allocator, 1630 sc_cipher: *Cipher, 1631 writer: *std.Io.Writer, 1632 ch: *Channel, 1633 want_reply: bool, 1634 success: bool, 1635 ) !void { 1636 if (!want_reply) return; 1637 var reply: std.ArrayList(u8) = .empty; 1638 defer reply.deinit(allocator); 1639 try reply.append(allocator, if (success) SSH_MSG_CHANNEL_SUCCESS else SSH_MSG_CHANNEL_FAILURE); 1640 try writeU32(&reply, allocator, ch.remote_id); 1641 try sc_cipher.writePacket(io, allocator, writer, reply.items); 1642 } 1643 1644 fn handleWindowAdjust(ch: *Channel, packet: []const u8) !void { 1645 // byte SSH_MSG_CHANNEL_WINDOW_ADJUST 1646 // uint32 recipient_channel 1647 // uint32 bytes_to_add 1648 var r = std.Io.Reader.fixed(packet[1..]); 1649 const recipient_channel = try r.takeInt(u32, .big); 1650 if (recipient_channel != ch.local_id) return error.UnknownChannel; 1651 const add = try r.takeInt(u32, .big); 1652 ch.remote_window +|= add; 1653 } 1654 1655 fn discardChannelData( 1656 io: std.Io, 1657 allocator: std.mem.Allocator, 1658 sc_cipher: *Cipher, 1659 writer: *std.Io.Writer, 1660 ch: *Channel, 1661 packet: []const u8, 1662 extended: bool, 1663 ) !void { 1664 // byte SSH_MSG_CHANNEL_DATA/EXTENDED_DATA 1665 // uint32 recipient_channel 1666 // [if extended: uint32 type_code] 1667 // string data 1668 const payload = try parseChannelData(packet, extended, ch.local_id); 1669 const data_len: u32 = @intCast(payload.len); 1670 1671 if (data_len > ch.local_window) return error.WindowExceeded; 1672 ch.local_window -= data_len; 1673 try maybeRefillRecvWindow(io, allocator, sc_cipher, writer, ch); 1674 } 1675 1676 pub fn parseChannelData(packet: []const u8, extended: bool, expected_channel: u32) ![]const u8 { 1677 if (packet.len < 1) return error.EmptyPacket; 1678 var r = std.Io.Reader.fixed(packet[1..]); 1679 const recipient_channel = try r.takeInt(u32, .big); 1680 if (recipient_channel != expected_channel) return error.UnknownChannel; 1681 if (extended) { 1682 const data_type = try r.takeInt(u32, .big); 1683 if (data_type != SSH_EXTENDED_DATA_STDERR) return error.UnsupportedExtendedData; 1684 } 1685 const data_len = try r.takeInt(u32, .big); 1686 // catches both data_len > remaining (would otherwise be a bounds-check 1687 // panic on the slice) and trailing junk after the declared payload. 1688 if (data_len != r.buffered().len) return error.InvalidChannelData; 1689 return r.buffered(); 1690 } 1691 1692 fn parseChannelId(packet: []const u8, expected_channel: u32) !void { 1693 if (packet.len < 1) return error.EmptyPacket; 1694 var r = std.Io.Reader.fixed(packet[1..]); 1695 const recipient_channel = try r.takeInt(u32, .big); 1696 if (recipient_channel != expected_channel) return error.UnknownChannel; 1697 if (r.buffered().len != 0) return error.InvalidChannelMessage; 1698 } 1699 1700 /// Send a CHANNEL_WINDOW_ADJUST if our receive window has dipped below half 1701 /// of the initial value. Used both for the pre-session discard path and by 1702 /// SessionCtx after it consumes a CHANNEL_DATA payload. 1703 fn maybeRefillRecvWindow( 1704 io: std.Io, 1705 allocator: std.mem.Allocator, 1706 sc_cipher: *Cipher, 1707 writer: *std.Io.Writer, 1708 ch: *Channel, 1709 ) !void { 1710 if (ch.local_window >= initial_recv_window / 2) return; 1711 const add = initial_recv_window - ch.local_window; 1712 ch.local_window += add; 1713 var adj: std.ArrayList(u8) = .empty; 1714 defer adj.deinit(allocator); 1715 try adj.append(allocator, SSH_MSG_CHANNEL_WINDOW_ADJUST); 1716 try writeU32(&adj, allocator, ch.remote_id); 1717 try writeU32(&adj, allocator, add); 1718 try sc_cipher.writePacket(io, allocator, writer, adj.items); 1719 } 1720 1721 pub fn writeU32(buf: *std.ArrayList(u8), allocator: std.mem.Allocator, value: u32) !void { 1722 var bytes: [4]u8 = undefined; 1723 std.mem.writeInt(u32, &bytes, value, .big); 1724 try buf.appendSlice(allocator, &bytes); 1725 } 1726