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Takashi Iwai c99be0d5af ALSA: aloop: Fix racy access at PCM trigger 
[ Upstream commit 826af7fa62 ]

The PCM trigger callback of aloop driver tries to check the PCM state
and stop the stream of the tied substream in the corresponding cable.
Since both check and stop operations are performed outside the cable
lock, this may result in UAF when a program attempts to trigger
frequently while opening/closing the tied stream, as spotted by
fuzzers.

For addressing the UAF, this patch changes two things:
- It covers the most of code in loopback_check_format() with
  cable->lock spinlock, and add the proper NULL checks.  This avoids
  already some racy accesses.
- In addition, now we try to check the state of the capture PCM stream
  that may be stopped in this function, which was the major pain point
  leading to UAF.

Reported-by: syzbot+5f8f3acdee1ec7a7ef7b@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/69783ba1.050a0220.c9109.0011.GAE@google.com
Cc: <stable@vger.kernel.org>
Link: https://patch.msgid.link/20260203141003.116584-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>
[ Karl Mehltretter: open-coded spin_lock_irqsave() instead of scoped_guard();
  used snd_pcm_running() instead of cruntime->state; dropped the access-mode
  comparison and notification (462494565c, e299a9fd43, cdac6e1f71);
  kept the stop_count handling from the e5c33cdc6f backport. ]
Assisted-by: LLM
Signed-off-by: Karl Mehltretter <kmehltretter@gmail.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2026-09-14 13:20:03 +02:00
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README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.