ALSA: seq: Avoid module auto-load handling at event delivery

snd_seq_client_use_ptr() is supposed to return the snd_seq_client
object for the given client ID, and it tries to handle the module
auto-loading when no matching object is found.  Although the module
handling is performed only conditionally with "!in_interrupt()", this
condition may be fragile, e.g. when the code is called from the ALSA
timer callback where the spinlock is temporarily disabled while the
irq is disabled.  Then his doesn't fit well and spews the error about
sleep from invalid context, as complained recently by syzbot.

Also, in general, handling the module-loading at each time if no
matching object is found is really an overkill.  It can be still
useful when performed at the top-level ioctl or proc reads, but it
shouldn't be done at event delivery at all.

For addressing the issues above, this patch disables the module
handling in snd_seq_client_use_ptr() in normal cases like event
deliveries, but allow only in limited and safe situations.
A new function client_load_and_use_ptr() is used for the cases where
the module loading can be done safely, instead.

Reported-by: syzbot+4cb9fad083898f54c517@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/67c272e5.050a0220.dc10f.0159.GAE@google.com
Cc: <stable@vger.kernel.org>
Link: https://patch.msgid.link/20250301114530.8975-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>

0 files changed, 0 insertions, 0 deletions