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ssh_terminal: avoid deadlock during bind callback

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Issue #4095
This commit is contained in:
Alexander Boettcher 2021-05-18 12:01:11 +02:00 committed by Christian Helmuth
parent 9166a75f2c
commit 9549eeeca4
2 changed files with 49 additions and 24 deletions
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68
repos/gems/src/server/ssh_terminal/server.cc
View File

@ -477,30 +477,15 @@ void Ssh::Server::incoming_connection(ssh_session s)
throw -1;
}
new (&_heap) Session(_sessions, s, &_channel_cb, ++_session_id);
ssh_set_server_callbacks(s, &_session_cb);
int auth_methods = SSH_AUTH_METHOD_UNKNOWN;
auth_methods += _allow_password ? SSH_AUTH_METHOD_PASSWORD : 0;
auth_methods += _allow_publickey ? SSH_AUTH_METHOD_PUBLICKEY : 0;
ssh_set_auth_methods(s, auth_methods);
/*
* Normally we would check the result of the key exchange
* function but for better or worse using callbacks leads to
* a false negative. So ignore any result and move on in hope
* that the callsbacks will handle the situation.
*
* FIXME investigate why it somtimes fails in the first place.
* Queue up new ssh_session to be enabled later in pthread ssh loop.
* We can't directly add the new Session object to the _session registry,
* because this ssh callback may be invoked from within a
* _session.for_each(...) invocation. The internal _session Genode::Mutex
* is taken during _session.for_each(...) and during a 'new' here,
* which would lead to a deadlock.
*/
int key_exchange_result = ssh_handle_key_exchange(s);
if (SSH_OK != key_exchange_result) {
Genode::warning("key exchange returned ", key_exchange_result);
}
ssh_event_add_session(_event_loop, s);
new (&_heap) Session(_new_sessions, s, &_channel_cb, ++_session_id);
}
@ -664,6 +649,45 @@ void Ssh::Server::loop()
};
_sessions.for_each(send);
}
/* enable all new sessions that got added by ssh callbacks */
auto activate = [&] (Session &inactive_session) {
/* re-queue session object */
new (&_heap) Session(_sessions,
inactive_session.session,
inactive_session.channel_cb,
inactive_session.id());
ssh_session s = inactive_session.session;
/* remove temporary object */
Genode::destroy(&_heap, &inactive_session);
/* activate session */
ssh_set_server_callbacks(s, &_session_cb);
int auth_methods = SSH_AUTH_METHOD_UNKNOWN;
auth_methods += _allow_password ? SSH_AUTH_METHOD_PASSWORD : 0;
auth_methods += _allow_publickey ? SSH_AUTH_METHOD_PUBLICKEY : 0;
ssh_set_auth_methods(s, auth_methods);
/*
* Normally we would check the result of the key exchange
* function but for better or worse using callbacks leads to
* a false negative. So ignore any result and move on in hope
* that the callsbacks will handle the situation.
*
* FIXME investigate why it somtimes fails in the first place.
*/
int key_exchange_result = ssh_handle_key_exchange(s);
if (SSH_OK != key_exchange_result) {
Genode::warning("key exchange returned ", key_exchange_result);
}
ssh_event_add_session(_event_loop, s);
};
_new_sessions.for_each(activate);
}
}

5
repos/gems/src/server/ssh_terminal/server.h
View File

@ -170,8 +170,9 @@ class Ssh::Server
ssh_server_callbacks_struct _session_cb { };
ssh_bind_callbacks_struct _bind_cb { };
Session_registry _sessions { };
uint32_t _session_id { 0 };
Session_registry _sessions { };
Session_registry _new_sessions { };
uint32_t _session_id { 0 };
void _initialize_channel_callbacks();
void _initialize_session_callbacks();