net/smc: don't spin in smc_rx_recvmsg() while a pipe holds spliced data

While bytes spliced off the RMB are still in a pipe, recvmsg() waits
for the pipe to release them before it copies the data behind them.
The path to that wait skips the timeout and signal checks, and
smc_rx_wait() returns at once on RCV_SHUTDOWN. With a signal pending,
after SHUT_RD, or once the peer closes or shuts down writing,
recvmsg() spins on a CPU until the pipe is drained, and SIGKILL cannot
stop it. MSG_DONTWAIT and an expired SO_RCVTIMEO wait there too
instead of returning -EAGAIN.

Check the timeout and signals before that wait, and end it when the
pipe releases the data or the connection is killed, not on RCV_SHUTDOWN.
A zero-length read returns 0 without waiting for the pipe; a
non-blocking one returns -EAGAIN while poll() still reports the socket
readable (splice() can still take those bytes). The wait sets
SOCKWQ_ASYNC_WAITDATA like smc_rx_wait(), so a byte arriving behind
the pipe raises no SIGIO on a reader already asleep for it, and a full
barrier orders its wait queue entry before its read of splice_pending,
so no wake is lost.

Fixes: 9014db202cb7 ("smc: add support for splice()")
Cc: stable@vger.kernel.org
Signed-off-by: Bryam Vargas <hexlabsecurity@proton.me>
Reviewed-by: Dust Li <dust.li@linux.alibaba.com>
Link: https://patch.msgid.link/20261029-b4-disp-da7f8e6a-v2-1-9052904adf72@proton.me
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

0 files changed, 0 insertions, 0 deletions