From: Paolo Abeni Date: Thu, 9 Mar 2023 14:49:57 +0000 (+0100) Subject: mptcp: fix possible deadlock in subflow_error_report X-Git-Tag: baikal/mips/sdk6.1~39 X-Git-Url: https://git.baikalelectronics.ru/sdk/?a=commitdiff_plain;h=7a43616ff6f2135e9d860ddb6e9bcefdc8fbc457;p=kernel.git mptcp: fix possible deadlock in subflow_error_report commit e374ba580cbaea99a6baf4cbab2ca07e52bdb871 upstream. 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. Reported-and-tested-by: Christoph Paasch Fixes: d9b41d28dae4 ("mptcp: deliver ssk errors to msk") Cc: stable@vger.kernel.org Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/355 Signed-off-by: Paolo Abeni Reviewed-by: Matthieu Baerts Signed-off-by: Matthieu Baerts Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman --- diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c index c4971bc42f60f..0bbaf26500e93 100644 --- a/net/mptcp/subflow.c +++ b/net/mptcp/subflow.c @@ -1376,6 +1376,13 @@ 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);