This is a note to let you know that I've just added the patch titled
mptcp: fix possible deadlock in subflow_error_report
to the 6.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
mptcp-fix-possible-deadlock-in-subflow_error_report.patch
and it can be found in the queue-6.1 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From b7a679ba7c652587b85294f4953f33ac0b756d40 Mon Sep 17 00:00:00 2001
From: Paolo Abeni <pabeni@xxxxxxxxxx>
Date: Thu, 9 Mar 2023 15:49:57 +0100
Subject: mptcp: fix possible deadlock in subflow_error_report
From: Paolo Abeni <pabeni@xxxxxxxxxx>
commit b7a679ba7c652587b85294f4953f33ac0b756d40 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 <cpaasch@xxxxxxxxx>
Fixes: 15cc10453398 ("mptcp: deliver ssk errors to msk")
Cc: stable@xxxxxxxxxxxxxxx
Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/355
Signed-off-by: Paolo Abeni <pabeni@xxxxxxxxxx>
Reviewed-by: Matthieu Baerts <matthieu.baerts@xxxxxxxxxxxx>
Signed-off-by: Matthieu Baerts <matthieu.baerts@xxxxxxxxxxxx>
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
net/mptcp/subflow.c | 7 +++++++
1 file changed, 7 insertions(+)
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -1376,6 +1376,13 @@ static void subflow_error_report(struct
{
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);
Patches currently in stable-queue which might be from pabeni@xxxxxxxxxx are
queue-6.1/mptcp-fix-possible-deadlock-in-subflow_error_report.patch
queue-6.1/mptcp-avoid-setting-tcp_close-state-twice.patch
queue-6.1/mptcp-fix-lockdep-false-positive-in-mptcp_pm_nl_create_listen_socket.patch
