From 41f171d9822f4dd8a26a58c4c365f9507053c15b Mon Sep 17 00:00:00 2001 From: John Safranek Date: Wed, 2 Sep 2026 09:40:30 -0700 Subject: [PATCH] agent: let the application open the agent channel The one server-side site that opens auth-agent@openssh.com sits inside wolfSSH_accept(), so an application driving its own channels cannot reach it: the session records the request and no channel follows. - add wolfSSH_AGENT_ChannelOpen(), the same open lifted out of accept(), which still calls it - it reports WS_BAD_ARGUMENT until the peer asks and on a client session, and is idempotent after, so an application can poll it - publish the agent on a queued open too, so a retry after WS_WANT_WRITE finds it rather than opening a second channel and leaking the first - flush what is left of a queued open on the next call, rather than reporting a success the peer never saw - record ssh->error from the send alone, so neither a poll ahead of the request nor a failed allocation stops accept() continuing --- src/agent.c | 78 ++++++++++++++++++++++++++++++++++++ src/ssh.c | 42 +------------------- tests/regress.c | 102 ++++++++++++++++++++++++++++++++++++++++++++++++ wolfssh/agent.h | 12 ++++++ 4 files changed, 193 insertions(+), 41 deletions(-) diff --git a/src/agent.c b/src/agent.c index 33c0eb93..f46d7296 100644 --- a/src/agent.c +++ b/src/agent.c @@ -1731,6 +1731,84 @@ int wolfSSH_AGENT_enable(WOLFSSH* ssh, byte isEnabled) } +int wolfSSH_AGENT_ChannelOpen(WOLFSSH* ssh) +{ + WOLFSSH_AGENT_CTX* newAgent = NULL; + WOLFSSH_CHANNEL* newChannel = NULL; + int ret = WS_SUCCESS; + /* wolfSSH_accept() clears only want-read/want-write/auth-pending, so a + * WS_BAD_ARGUMENT latched by a poll kills the handshake. */ + int recordError = 0; + + WLOG_ENTER(); + + if (ssh == NULL) + ret = WS_SSH_NULL_E; + else if (ssh->ctx->side != WOLFSSH_ENDPOINT_SERVER) { + /* Server side only. wolfSSH_connect() sets ssh->agent too, so the + * checks below would report a channel a client never opened. */ + ret = WS_BAD_ARGUMENT; + } + else if (!ssh->useAgent) { + /* Nothing asked for agent forwarding on this session. */ + ret = WS_BAD_ARGUMENT; + } + else if (ssh->agent == NULL) { + /* Nothing else sets ssh->agent, so a NULL one means "not opened + * yet". Idempotent, so a poll cannot open a second channel. */ + WLOG(WS_LOG_AGENT, "Starting agent channel"); + + newAgent = wolfSSH_AGENT_new(ssh->ctx->heap); + if (newAgent == NULL) + ret = WS_MEMORY_E; + + if (ret == WS_SUCCESS) { + newChannel = ChannelNew(ssh, ID_CHANTYPE_AUTH_AGENT, + ssh->ctx->windowSz, ssh->ctx->maxPacketSz); + if (newChannel == NULL) + ret = WS_MEMORY_E; + } + + if (ret == WS_SUCCESS) { + recordError = 1; + ret = SendChannelOpenSession(ssh, newChannel); + + if (ret < WS_SUCCESS + && ret != WS_WANT_WRITE && ret != WS_WANT_READ) { + ChannelDelete(newChannel, ssh->ctx->heap); + } + else { + /* Publish on a queued open too, so a retry takes the + * already-open path rather than opening a second. */ + ChannelAppend(ssh, newChannel); + newAgent->channel = newChannel->channel; + ssh->agent = newAgent; + newAgent = NULL; + if (ssh->ctx->agentCb) { + ssh->ctx->agentCb(WOLFSSH_AGENT_LOCAL_SETUP, + ssh->agentCbCtx); + } + } + } + + if (newAgent != NULL) + wolfSSH_AGENT_free(newAgent); + } + else if (wolfSSH_OutputPending(ssh)) { + /* Any queued output, not just this open. Flush it rather than + * report a success the peer hasn't seen. */ + recordError = 1; + ret = wolfSSH_SendPacket(ssh); + } + + if (recordError) + ssh->error = ret; + + WLOG_LEAVE(ret); + return ret; +} + + int wolfSSH_AGENT_worker(WOLFSSH* ssh) { int ret = WS_SUCCESS; diff --git a/src/ssh.c b/src/ssh.c index 56caf400..5f5591dc 100644 --- a/src/ssh.c +++ b/src/ssh.c @@ -813,52 +813,12 @@ int wolfSSH_accept(WOLFSSH* ssh) #endif /* WOLFSSH_SFTP and !NO_WOLFSSH_SERVER */ #ifdef WOLFSSH_AGENT if (ssh->useAgent) { - WOLFSSH_AGENT_CTX* newAgent; - WOLFSSH_CHANNEL* newChannel; - - WLOG(WS_LOG_AGENT, "Starting agent channel"); - - newAgent = wolfSSH_AGENT_new(ssh->ctx->heap); - if (newAgent == NULL) { - ssh->error = WS_MEMORY_E; - WLOG(WS_LOG_DEBUG, acceptError, - "SERVER_USERAUTH_ACCEPT_DONE", ssh->error); - return WS_ERROR; - } - - newChannel = ChannelNew(ssh, ID_CHANTYPE_AUTH_AGENT, - ssh->ctx->windowSz, ssh->ctx->maxPacketSz); - if (newChannel == NULL) { - wolfSSH_AGENT_free(newAgent); - ssh->error = WS_MEMORY_E; - WLOG(WS_LOG_DEBUG, acceptError, - "SERVER_USERAUTH_ACCEPT_DONE", ssh->error); - return WS_FATAL_ERROR; - } - - ssh->error = SendChannelOpenSession(ssh, newChannel); + ssh->error = wolfSSH_AGENT_ChannelOpen(ssh); if (ssh->error < WS_SUCCESS) { - if (ssh->error == WS_WANT_WRITE || - ssh->error == WS_WANT_READ) { - ChannelAppend(ssh, newChannel); - } - else { - ChannelDelete(newChannel, ssh->ctx->heap); - wolfSSH_AGENT_free(newAgent); - } WLOG(WS_LOG_DEBUG, acceptError, "SERVER_USERAUTH_ACCEPT_DONE", ssh->error); return WS_FATAL_ERROR; } - ChannelAppend(ssh, newChannel); - newAgent->channel = newChannel->channel; - if (ssh->ctx->agentCb) { - ssh->ctx->agentCb(WOLFSSH_AGENT_LOCAL_SETUP, - ssh->agentCbCtx); - } - if (ssh->agent != NULL) - wolfSSH_AGENT_free(ssh->agent); - ssh->agent = newAgent; } #endif /* WOLFSSH_AGENT */ ssh->acceptState = ACCEPT_CLIENT_SESSION_ESTABLISHED; diff --git a/tests/regress.c b/tests/regress.c index c87c888d..3c248d99 100644 --- a/tests/regress.c +++ b/tests/regress.c @@ -4437,6 +4437,102 @@ static void TestAgentChannelNullAgentSendsOpenFail(void) FreeChannelOpenHarness(&harness); } + +/* Nothing asked for forwarding, so the open is refused rather than started. + * The refusal is the documented answer to a poll, so it must not land in + * ssh->error: wolfSSH_accept() would then abort with WS_INVALID_STATE_E. */ +static void TestAgentChannelOpenWithoutRequest(void) +{ + ChannelOpenHarness harness; + + InitChannelOpenHarness(&harness, NULL, 0); + + AssertIntEQ(wolfSSH_AGENT_ChannelOpen(harness.ssh), WS_BAD_ARGUMENT); + AssertNull(harness.ssh->agent); + AssertIntEQ(harness.io.outSz, 0); + AssertIntEQ(harness.ssh->error, WS_SUCCESS); + + /* The handshake survives the poll: no input, so accept only wants read. */ + AssertIntEQ(wolfSSH_accept(harness.ssh), WS_FATAL_ERROR); + AssertIntEQ(harness.ssh->error, WS_WANT_READ); + + FreeChannelOpenHarness(&harness); +} + +/* A queued open publishes the agent, so the caller's next poll must finish + * the send rather than report a success the peer never saw, and must not + * open a second channel. */ +static void TestAgentChannelOpenFlushesQueuedOpen(void) +{ + ChannelOpenHarness harness; + word32 outSz; + + InitChannelOpenHarness(&harness, NULL, 0); + harness.ssh->useAgent = 1; + harness.io.blockNext = 1; + + AssertIntEQ(wolfSSH_AGENT_ChannelOpen(harness.ssh), WS_WANT_WRITE); + AssertNotNull(harness.ssh->agent); + AssertIntEQ(harness.ssh->channelListSz, 1); + AssertIntEQ(harness.io.outSz, 0); + + AssertIntEQ(wolfSSH_AGENT_ChannelOpen(harness.ssh), WS_SUCCESS); + AssertIntEQ(harness.ssh->channelListSz, 1); + AssertTrue(harness.io.outSz > 0); + AssertIntEQ(ParseMsgId(harness.io.out, harness.io.outSz), + MSGID_CHANNEL_OPEN); + + /* The flushed open is the answer wolfSSH_accept() retries on: success, + * no second channel, no new packet, ssh->error untouched. */ + outSz = harness.io.outSz; + harness.ssh->error = WS_SUCCESS; + + AssertIntEQ(wolfSSH_AGENT_ChannelOpen(harness.ssh), WS_SUCCESS); + AssertIntEQ(harness.ssh->channelListSz, 1); + AssertIntEQ(harness.io.outSz, outSz); + AssertIntEQ(harness.ssh->error, WS_SUCCESS); + + FreeChannelOpenHarness(&harness); +} + +/* A send that fails outright, rather than blocking, leaves nothing behind, + * so a later poll starts the open over. */ +static void TestAgentChannelOpenSendFailureCleansUp(void) +{ + ChannelOpenHarness harness; + + InitChannelOpenHarness(&harness, NULL, 0); + harness.ssh->useAgent = 1; + /* No room, so MemSend reports a general error. */ + harness.io.outCap = 0; + + AssertIntEQ(wolfSSH_AGENT_ChannelOpen(harness.ssh), WS_SOCKET_ERROR_E); + AssertNull(harness.ssh->agent); + AssertIntEQ(harness.ssh->channelListSz, 0); + AssertIntEQ(harness.io.outSz, 0); + AssertIntEQ(harness.ssh->error, WS_SOCKET_ERROR_E); + + FreeChannelOpenHarness(&harness); +} + +#ifndef NO_WOLFSSH_CLIENT +/* Server-side call. A client has an ssh->agent of its own, so answering the + * poll from it would report a channel that was never opened. */ +static void TestAgentChannelOpenOnClientRefused(void) +{ + ChannelOpenHarness harness; + + InitChannelOpenHarnessClient(&harness, NULL, 0); + harness.ssh->useAgent = 1; + + AssertIntEQ(wolfSSH_AGENT_ChannelOpen(harness.ssh), WS_BAD_ARGUMENT); + AssertIntEQ(harness.ssh->channelListSz, 0); + AssertIntEQ(harness.io.outSz, 0); + AssertIntEQ(harness.ssh->error, WS_SUCCESS); + + FreeChannelOpenHarness(&harness); +} +#endif /* !NO_WOLFSSH_CLIENT */ #endif @@ -13427,6 +13523,12 @@ int main(int argc, char** argv) #endif #ifdef WOLFSSH_AGENT TestAgentChannelNullAgentSendsOpenFail(); + TestAgentChannelOpenWithoutRequest(); + TestAgentChannelOpenFlushesQueuedOpen(); + TestAgentChannelOpenSendFailureCleansUp(); +#ifndef NO_WOLFSSH_CLIENT + TestAgentChannelOpenOnClientRefused(); +#endif #endif #endif /* NO_WOLFSSH_SERVER */ #if defined(WOLFSSH_AGENT) && !defined(WOLFSSH_NO_ED25519) \ diff --git a/wolfssh/agent.h b/wolfssh/agent.h index 581e3eba..8f57bc5d 100644 --- a/wolfssh/agent.h +++ b/wolfssh/agent.h @@ -181,6 +181,18 @@ WOLFSSH_API int wolfSSH_CTX_set_agent_cb(WOLFSSH_CTX* ctx, WOLFSSH_API int wolfSSH_set_agent_cb_ctx(WOLFSSH* ssh, void* ctx); WOLFSSH_API int wolfSSH_CTX_AGENT_enable(WOLFSSH_CTX* ctx, byte isEnabled); WOLFSSH_API int wolfSSH_AGENT_enable(WOLFSSH* ssh, byte isEnabled); +/* Server side. Opens the auth-agent@openssh.com channel to the client once + * the peer's auth-agent-req@openssh.com asks for forwarding. wolfSSH_accept() + * does it on the default path; an application driving its own channels polls + * this instead. Opens one channel, then flushes what of the open is queued. + * Returns WS_SUCCESS, WS_BAD_ARGUMENT before the peer asks or on a client + * session, WS_WANT_READ or WS_WANT_WRITE while output is still queued, + * WS_SSH_NULL_E, WS_MEMORY_E, or whatever the send reports. WS_SUCCESS says + * the open went out, not that the peer took it; a refusal reaches the + * channel-open-fail callback. + * Only the send records in ssh->error, so a poll ahead of the peer's request + * leaves the session fit for wolfSSH_accept(). */ +WOLFSSH_API int wolfSSH_AGENT_ChannelOpen(WOLFSSH* ssh); WOLFSSH_LOCAL int wolfSSH_AGENT_worker(WOLFSSH* ssh); WOLFSSH_API int wolfSSH_AGENT_Relay(WOLFSSH* ssh, const byte* msg, word32* msgSz, byte* rsp, word32* rspSz);