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    • Takashi Iwai's avatar
      ALSA: pcm: Fix potential AB/BA lock with buffer_mutex and mmap_lock · bc55cfd5
      Takashi Iwai authored
      syzbot caught a potential deadlock between the PCM
      runtime->buffer_mutex and the mm->mmap_lock.  It was brought by the
      recent fix to cover the racy read/write and other ioctls, and in that
      commit, I overlooked a (hopefully only) corner case that may take the
      revert lock, namely, the OSS mmap.  The OSS mmap operation
      exceptionally allows to re-configure the parameters inside the OSS
      mmap syscall, where mm->mmap_mutex is already held.  Meanwhile, the
      copy_from/to_user calls at read/write operations also take the
      mm->mmap_lock internally, hence it may lead to a AB/BA deadlock.
      
      A similar problem was already seen in the past and we fixed it with a
      refcount (in commit b2483716
      
      ).  The former fix covered only the
      call paths with OSS read/write and OSS ioctls, while we need to cover
      the concurrent access via both ALSA and OSS APIs now.
      
      This patch addresses the problem above by replacing the buffer_mutex
      lock in the read/write operations with a refcount similar as we've
      used for OSS.  The new field, runtime->buffer_accessing, keeps the
      number of concurrent read/write operations.  Unlike the former
      buffer_mutex protection, this protects only around the
      copy_from/to_user() calls; the other codes are basically protected by
      the PCM stream lock.  The refcount can be a negative, meaning blocked
      by the ioctls.  If a negative value is seen, the read/write aborts
      with -EBUSY.  In the ioctl side, OTOH, they check this refcount, too,
      and set to a negative value for blocking unless it's already being
      accessed.
      
      Reported-by: default avatar <syzbot+6e5c88838328e99c7e1c@syzkaller.appspotmail.com>
      Fixes: dca947d4 ("ALSA: pcm: Fix races among concurrent read/write and buffer changes")
      Cc: <stable@vger.kernel.org>
      Link: https://lore.kernel.org/r/000000000000381a0d05db622a81@google.com
      Link: https://lore.kernel.org/r/20220330120903.4738-1-tiwai@suse.de
      
      
      Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
      bc55cfd5
    • Takashi Iwai's avatar
      Merge tag 'asoc-fix-v5.18' of... · 21b5954d
      Takashi Iwai authored
      Merge tag 'asoc-fix-v5.18' of https://git.kernel.org/pub/scm/linux/kernel/git/broonie/sound into for-linus
      
      ASoC: Fixes for v5.18
      
      A few fixes that came in during the merge window, all fairly routine.
      21b5954d