From: Paolo Abeni pabeni@redhat.com
Christoph reported a possible deadlock while the TCP stack destroys an unaccepted subflow due to an incoming reset: the MPTCP socket error path tries to acquire the msk-level socket lock while TCP still owns the listener socket accept queue spinlock, and the reverse dependency already exists in the TCP stack.
Note that the above is actually a lockdep false positive, as the chain involves two separate sockets. A different per-socket lockdep key will address the issue, but such a change will be quite invasive.
Instead, we can simply stop earlier the socket error handling for orphaned or unaccepted subflows, breaking the critical lockdep chain. Error handling in such a scenario is a no-op.
Fixes: 15cc10453398 ("mptcp: deliver ssk errors to msk") Cc: stable@vger.kernel.org Reported-and-tested-by: Christoph Paasch cpaasch@apple.com Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/355 Signed-off-by: Paolo Abeni pabeni@redhat.com Reviewed-by: Matthieu Baerts matthieu.baerts@tessares.net Signed-off-by: Matthieu Baerts matthieu.baerts@tessares.net --- net/mptcp/subflow.c | 7 +++++++ 1 file changed, 7 insertions(+)
diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c index 4ae1a7304cf0..5070dc33675d 100644 --- a/net/mptcp/subflow.c +++ b/net/mptcp/subflow.c @@ -1432,6 +1432,13 @@ static void subflow_error_report(struct sock *ssk) { struct sock *sk = mptcp_subflow_ctx(ssk)->conn;
+ /* bail early if this is a no-op, so that we avoid introducing a + * problematic lockdep dependency between TCP accept queue lock + * and msk socket spinlock + */ + if (!sk->sk_socket) + return; + mptcp_data_lock(sk); if (!sock_owned_by_user(sk)) __mptcp_error_report(sk);