Hi!

> commit 80982c7e834e5d4e325b6ce33757012ecafdf0bb upstream.
> 
> Some ioctls via OSS sequencer API may race and lead to UAF when the
> port create and delete are performed concurrently, as spotted by a
> couple of syzkaller cases.  This patch is an attempt to address it by
> serializing the ioctls with the existing register_mutex.
> 
> Basically OSS sequencer API is an obsoleted interface and was designed
> without much consideration of the concurrency.  There are very few
> applications with it, and the concurrent performance isn't asked,
> hence this "big hammer" approach should be good enough.

That really is a "big hammer". And I believe it is too big.

In particular, do we need to drop the lock while sleeping in
SNDCTL_SEQ_SYNC: => snd_seq_oss_writeq_sync ?

Best regards,
								Pavel
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