From 29d7533c715f972ee996382c2c45cc0c055e10d2 Mon Sep 17 00:00:00 2001 From: Hans Nilsson Date: Mon, 10 Apr 2017 16:25:06 +0200 Subject: ssh: Implement ext-info extension. draft-ietf-curdle-ssh-ext-info This is only a draft extension, but it is quite stable and already supported by some implementations. OpenSSH has had it for some year now. --- lib/ssh/src/ssh_transport.erl | 221 ++++++++++++++++++++++++++++-------------- 1 file changed, 147 insertions(+), 74 deletions(-) (limited to 'lib/ssh/src/ssh_transport.erl') diff --git a/lib/ssh/src/ssh_transport.erl b/lib/ssh/src/ssh_transport.erl index 6b47868d5c..d623d24529 100644 --- a/lib/ssh/src/ssh_transport.erl +++ b/lib/ssh/src/ssh_transport.erl @@ -38,6 +38,7 @@ handle_hello_version/1, key_exchange_init_msg/1, key_init/3, new_keys_message/1, + ext_info_message/1, handle_kexinit_msg/3, handle_kexdh_init/2, handle_kex_dh_gex_group/2, handle_kex_dh_gex_init/2, handle_kex_dh_gex_reply/2, handle_new_keys/2, handle_kex_dh_gex_request/2, @@ -230,7 +231,7 @@ key_exchange_init_msg(Ssh0) -> kex_init(#ssh{role = Role, opts = Opts, available_host_keys = HostKeyAlgs}) -> Random = ssh_bits:random(16), PrefAlgs = ?GET_OPT(preferred_algorithms, Opts), - kexinit_message(Role, Random, PrefAlgs, HostKeyAlgs). + kexinit_message(Role, Random, PrefAlgs, HostKeyAlgs, Opts). key_init(client, Ssh, Value) -> Ssh#ssh{c_keyinit = Value}; @@ -238,10 +239,11 @@ key_init(server, Ssh, Value) -> Ssh#ssh{s_keyinit = Value}. -kexinit_message(_Role, Random, Algs, HostKeyAlgs) -> +kexinit_message(Role, Random, Algs, HostKeyAlgs, Opts) -> #ssh_msg_kexinit{ cookie = Random, - kex_algorithms = to_strings( get_algs(kex,Algs) ), + kex_algorithms = to_strings( get_algs(kex,Algs) ) + ++ kex_ext_info(Role,Opts), server_host_key_algorithms = HostKeyAlgs, encryption_algorithms_client_to_server = c2s(cipher,Algs), encryption_algorithms_server_to_client = s2c(cipher,Algs), @@ -263,39 +265,42 @@ get_algs(Key, Algs) -> proplists:get_value(Key, Algs, default_algorithms(Key)). to_strings(L) -> lists:map(fun erlang:atom_to_list/1, L). new_keys_message(Ssh0) -> - {SshPacket, Ssh} = - ssh_packet(#ssh_msg_newkeys{}, Ssh0), + {SshPacket, Ssh1} = ssh_packet(#ssh_msg_newkeys{}, Ssh0), + Ssh = install_alg(snd, Ssh1), {ok, SshPacket, Ssh}. handle_kexinit_msg(#ssh_msg_kexinit{} = CounterPart, #ssh_msg_kexinit{} = Own, - #ssh{role = client} = Ssh0) -> - {ok, Algoritms} = select_algorithm(client, Own, CounterPart), - case verify_algorithm(Algoritms) of - true -> - key_exchange_first_msg(Algoritms#alg.kex, - Ssh0#ssh{algorithms = Algoritms}); - {false,Alg} -> - %% TODO: Correct code? - ssh_connection_handler:disconnect( - #ssh_msg_disconnect{code = ?SSH_DISCONNECT_KEY_EXCHANGE_FAILED, - description = "Selection of key exchange algorithm failed: " - ++ Alg - }) + #ssh{role = client} = Ssh) -> + try + {ok, Algorithms} = select_algorithm(client, Own, CounterPart, Ssh#ssh.opts), + true = verify_algorithm(Algorithms), + Algorithms + of + Algos -> + key_exchange_first_msg(Algos#alg.kex, + Ssh#ssh{algorithms = Algos}) + catch + _:_ -> + ssh_connection_handler:disconnect( + #ssh_msg_disconnect{code = ?SSH_DISCONNECT_KEY_EXCHANGE_FAILED, + description = "Selection of key exchange algorithm failed"}) end; handle_kexinit_msg(#ssh_msg_kexinit{} = CounterPart, #ssh_msg_kexinit{} = Own, - #ssh{role = server} = Ssh) -> - {ok, Algoritms} = select_algorithm(server, CounterPart, Own), - case verify_algorithm(Algoritms) of - true -> - {ok, Ssh#ssh{algorithms = Algoritms}}; - {false,Alg} -> - ssh_connection_handler:disconnect( - #ssh_msg_disconnect{code = ?SSH_DISCONNECT_KEY_EXCHANGE_FAILED, - description = "Selection of key exchange algorithm failed: " - ++ Alg - }) + #ssh{role = server} = Ssh) -> + try + {ok, Algorithms} = select_algorithm(server, CounterPart, Own, Ssh#ssh.opts), + true = verify_algorithm(Algorithms), + Algorithms + of + Algos -> + {ok, Ssh#ssh{algorithms = Algos}} + catch + _:_ -> + ssh_connection_handler:disconnect( + #ssh_msg_disconnect{code = ?SSH_DISCONNECT_KEY_EXCHANGE_FAILED, + description = "Selection of key exchange algorithm failed"}) end. @@ -308,6 +313,8 @@ verify_algorithm(#alg{decrypt = undefined}) -> {false, "decrypt"}; verify_algorithm(#alg{compress = undefined}) -> {false, "compress"}; verify_algorithm(#alg{decompress = undefined}) -> {false, "decompress"}; verify_algorithm(#alg{kex = Kex}) -> + %% This also catches the error if 'ext-info-s' or 'ext-info-c' is selected. + %% (draft-ietf-curdle-ssh-ext-info-04 2.2) case lists:member(Kex, supported_algorithms(kex)) of true -> true; false -> {false, "kex"} @@ -414,9 +421,9 @@ handle_kexdh_reply(#ssh_msg_kexdh_reply{public_host_key = PeerPubHostKey, case verify_host_key(Ssh0, PeerPubHostKey, H, H_SIG) of ok -> {SshPacket, Ssh} = ssh_packet(#ssh_msg_newkeys{}, Ssh0), - {ok, SshPacket, Ssh#ssh{shared_secret = ssh_bits:mpint(K), - exchanged_hash = H, - session_id = sid(Ssh, H)}}; + {ok, SshPacket, install_alg(snd, Ssh#ssh{shared_secret = ssh_bits:mpint(K), + exchanged_hash = H, + session_id = sid(Ssh, H)})}; Error -> ssh_connection_handler:disconnect( #ssh_msg_disconnect{ @@ -584,9 +591,9 @@ handle_kex_dh_gex_reply(#ssh_msg_kex_dh_gex_reply{public_host_key = PeerPubHostK case verify_host_key(Ssh0, PeerPubHostKey, H, H_SIG) of ok -> {SshPacket, Ssh} = ssh_packet(#ssh_msg_newkeys{}, Ssh0), - {ok, SshPacket, Ssh#ssh{shared_secret = ssh_bits:mpint(K), - exchanged_hash = H, - session_id = sid(Ssh, H)}}; + {ok, SshPacket, install_alg(snd, Ssh#ssh{shared_secret = ssh_bits:mpint(K), + exchanged_hash = H, + session_id = sid(Ssh, H)})}; _Error -> ssh_connection_handler:disconnect( #ssh_msg_disconnect{ @@ -660,9 +667,9 @@ handle_kex_ecdh_reply(#ssh_msg_kex_ecdh_reply{public_host_key = PeerPubHostKey, case verify_host_key(Ssh0, PeerPubHostKey, H, H_SIG) of ok -> {SshPacket, Ssh} = ssh_packet(#ssh_msg_newkeys{}, Ssh0), - {ok, SshPacket, Ssh#ssh{shared_secret = ssh_bits:mpint(K), - exchanged_hash = H, - session_id = sid(Ssh, H)}}; + {ok, SshPacket, install_alg(snd, Ssh#ssh{shared_secret = ssh_bits:mpint(K), + exchanged_hash = H, + session_id = sid(Ssh, H)})}; Error -> ssh_connection_handler:disconnect( #ssh_msg_disconnect{ @@ -682,7 +689,7 @@ handle_kex_ecdh_reply(#ssh_msg_kex_ecdh_reply{public_host_key = PeerPubHostKey, %%%---------------------------------------------------------------- handle_new_keys(#ssh_msg_newkeys{}, Ssh0) -> - try install_alg(Ssh0) of + try install_alg(rcv, Ssh0) of #ssh{} = Ssh -> {ok, Ssh} catch @@ -693,6 +700,34 @@ handle_new_keys(#ssh_msg_newkeys{}, Ssh0) -> }) end. + +%%%---------------------------------------------------------------- +kex_ext_info(Role, Opts) -> + case ?GET_OPT(recv_ext_info,Opts) of + true when Role==client -> ["ext-info-c"]; + true when Role==server -> ["ext-info-s"]; + false -> [] + end. + +ext_info_message(#ssh{role=client, + algorithms=#alg{send_ext_info=true}} = Ssh0) -> + %% FIXME: no extensions implemented for clients + {ok, "", Ssh0}; + +ext_info_message(#ssh{role=server, + algorithms=#alg{send_ext_info=true}} = Ssh0) -> + AlgsList = lists:map(fun erlang:atom_to_list/1, + ssh_transport:default_algorithms(public_key)), + Msg = #ssh_msg_ext_info{nr_extensions = 1, + data = [{"server-sig-algs", string:join(AlgsList,",")}] + }, + {SshPacket, Ssh} = ssh_packet(Msg, Ssh0), + {ok, SshPacket, Ssh}; + +ext_info_message(Ssh0) -> + {ok, "", Ssh0}. % "" means: 'do not send' + +%%%---------------------------------------------------------------- %% select session id sid(#ssh{session_id = undefined}, H) -> H; @@ -812,7 +847,7 @@ known_host_key(#ssh{opts = Opts, key_cb = {KeyCb,KeyCbOpts}, peer = {PeerName,_} %% %% The first algorithm in each list MUST be the preferred (guessed) %% algorithm. Each string MUST contain at least one algorithm name. -select_algorithm(Role, Client, Server) -> +select_algorithm(Role, Client, Server, Opts) -> {Encrypt0, Decrypt0} = select_encrypt_decrypt(Role, Client, Server), {SendMac0, RecvMac0} = select_send_recv_mac(Role, Client, Server), @@ -837,17 +872,34 @@ select_algorithm(Role, Client, Server) -> Kex = select(Client#ssh_msg_kexinit.kex_algorithms, Server#ssh_msg_kexinit.kex_algorithms), - Alg = #alg{kex = Kex, - hkey = HK, - encrypt = Encrypt, - decrypt = Decrypt, - send_mac = SendMac, - recv_mac = RecvMac, - compress = Compression, - decompress = Decompression, - c_lng = C_Lng, - s_lng = S_Lng}, - {ok, Alg}. + SendExtInfo = + %% To send we must have that option enabled and ... + ?GET_OPT(send_ext_info,Opts) andalso + %% ... the peer must have told us to send: + case Role of + server -> lists:member("ext-info-c", Client#ssh_msg_kexinit.kex_algorithms); + client -> lists:member("ext-info-s", Server#ssh_msg_kexinit.kex_algorithms) + end, + + RecvExtInfo = + %% The peer should not send unless told so by us (which is + %% guided by an option). + %% (However a malicious peer could send anyway, so we must be prepared) + ?GET_OPT(recv_ext_info,Opts), + + {ok, #alg{kex = Kex, + hkey = HK, + encrypt = Encrypt, + decrypt = Decrypt, + send_mac = SendMac, + recv_mac = RecvMac, + compress = Compression, + decompress = Decompression, + c_lng = C_Lng, + s_lng = S_Lng, + send_ext_info = SendExtInfo, + recv_ext_info = RecvExtInfo + }}. %%% It is an agreed problem with RFC 5674 that if the selection is @@ -928,45 +980,66 @@ select_compression_decompression(server, Client, Server) -> Server#ssh_msg_kexinit.compression_algorithms_server_to_client), {Compression, Decompression}. -install_alg(SSH) -> - SSH1 = alg_final(SSH), - SSH2 = alg_setup(SSH1), - alg_init(SSH2). +%% DIr = rcv | snd +install_alg(Dir, SSH) -> + SSH1 = alg_final(Dir, SSH), + SSH2 = alg_setup(Dir, SSH1), + alg_init(Dir, SSH2). -alg_setup(SSH) -> +alg_setup(snd, SSH) -> ALG = SSH#ssh.algorithms, SSH#ssh{kex = ALG#alg.kex, hkey = ALG#alg.hkey, encrypt = ALG#alg.encrypt, - decrypt = ALG#alg.decrypt, send_mac = ALG#alg.send_mac, send_mac_size = mac_digest_size(ALG#alg.send_mac), + compress = ALG#alg.compress, + c_lng = ALG#alg.c_lng, + s_lng = ALG#alg.s_lng, + send_ext_info = ALG#alg.send_ext_info, + recv_ext_info = ALG#alg.recv_ext_info + }; + +alg_setup(rcv, SSH) -> + ALG = SSH#ssh.algorithms, + SSH#ssh{kex = ALG#alg.kex, + hkey = ALG#alg.hkey, + decrypt = ALG#alg.decrypt, recv_mac = ALG#alg.recv_mac, recv_mac_size = mac_digest_size(ALG#alg.recv_mac), - compress = ALG#alg.compress, decompress = ALG#alg.decompress, c_lng = ALG#alg.c_lng, s_lng = ALG#alg.s_lng, - algorithms = undefined + send_ext_info = ALG#alg.send_ext_info, + recv_ext_info = ALG#alg.recv_ext_info }. -alg_init(SSH0) -> + +alg_init(snd, SSH0) -> {ok,SSH1} = send_mac_init(SSH0), - {ok,SSH2} = recv_mac_init(SSH1), - {ok,SSH3} = encrypt_init(SSH2), - {ok,SSH4} = decrypt_init(SSH3), - {ok,SSH5} = compress_init(SSH4), - {ok,SSH6} = decompress_init(SSH5), - SSH6. - -alg_final(SSH0) -> + {ok,SSH2} = encrypt_init(SSH1), + {ok,SSH3} = compress_init(SSH2), + SSH3; + +alg_init(rcv, SSH0) -> + {ok,SSH1} = recv_mac_init(SSH0), + {ok,SSH2} = decrypt_init(SSH1), + {ok,SSH3} = decompress_init(SSH2), + SSH3. + + +alg_final(snd, SSH0) -> {ok,SSH1} = send_mac_final(SSH0), - {ok,SSH2} = recv_mac_final(SSH1), - {ok,SSH3} = encrypt_final(SSH2), - {ok,SSH4} = decrypt_final(SSH3), - {ok,SSH5} = compress_final(SSH4), - {ok,SSH6} = decompress_final(SSH5), - SSH6. + {ok,SSH2} = encrypt_final(SSH1), + {ok,SSH3} = compress_final(SSH2), + SSH3; + +alg_final(rcv, SSH0) -> + {ok,SSH1} = recv_mac_final(SSH0), + {ok,SSH2} = decrypt_final(SSH1), + {ok,SSH3} = decompress_final(SSH2), + SSH3. + select_all(CL, SL) when length(CL) + length(SL) < ?MAX_NUM_ALGORITHMS -> A = CL -- SL, %% algortihms only used by client -- cgit v1.2.3