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Cássio Gabriel
03f52a9c17
[ Upstream commite5c33cdc6f] loopback_check_format() may stop the capture side when playback starts with parameters that no longer match a running capture stream. Commit826af7fa62("ALSA: aloop: Fix racy access at PCM trigger") moved the peer lookup under cable->lock, but the actual snd_pcm_stop() still runs after dropping that lock. A concurrent close can clear the capture entry from cable->streams[] and detach or free its runtime while the playback trigger path still holds a stale peer substream pointer. Keep a per-cable count of in-flight peer stops before dropping cable->lock, and make free_cable() wait for those stops before detaching the runtime. This preserves the existing behavior while making the peer runtime lifetime explicit. Reported-by: syzbot+8fa95c41eafbc9d2ff6f@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=8fa95c41eafbc9d2ff6f Fixes:597603d615("ALSA: introduce the snd-aloop module for the PCM loopback") Cc: stable@vger.kernel.org Suggested-by: Takashi Iwai <tiwai@suse.com> Signed-off-by: Cássio Gabriel <cassiogabrielcontato@gmail.com> Link: https://patch.msgid.link/20260424-alsa-aloop-peer-stop-uaf-v2-1-94e68101db8a@gmail.com Signed-off-by: Takashi Iwai <tiwai@suse.de> [ used scoped_guard(spinlock_irq) instead of guard(spinlock_irq) ] Signed-off-by: Sasha Levin <sashal@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>