linux-kernel - [BUG] ALSA: core: seq: a possible double-lock bug in snd_seq_midisynth

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Date:   Mon, 29 Jul 2019 11:54:07 +0800
From:   Jia-Ju Bai <baijiaju1990@...il.com>
To:     perex@...ex.cz, Takashi Iwai <tiwai@...e.de>,
        gregkh@...uxfoundation.org, rfontana@...hat.com,
        allison@...utok.net, tglx@...utronix.de
Cc:     alsa-devel@...a-project.org, linux-kernel@...r.kernel.org
Subject: [BUG] ALSA: core: seq: a possible double-lock bug in
 snd_seq_midisynth_remove()

In snd_seq_midisynth_remove(), there is a possible double-lock bug:
snd_seq_midisynth_remove()
     mutex_lock(&register_mutex); -- line 421
     snd_seq_delete_kernel_client() --- line 436
         seq_free_client() -- line 2244
             mutex_lock(&register_mutex); -- line 294

This bug is found by a static analysis tool STCheck written by us.

I do not know how to correctly fix this bug, so I only report it.
A possible fix is to release the mutex lock before calling 
seq_free_client() in snd_seq_delete_kernel_client() and then acquiring 
the lock again after calling seq_free_client().


Best wishes,
Jia-Ju Bai