From: Takashi Iwai Date: Wed, 15 Jan 2020 20:37:33 +0000 (+0100) Subject: ALSA: seq: Fix racy access for queue timer in proc read X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=18832468753f6b58768fb2817625f30c1635fb90;p=GitHub%2FLineageOS%2FG12%2Fandroid_kernel_amlogic_linux-4.9.git ALSA: seq: Fix racy access for queue timer in proc read commit 60adcfde92fa40fcb2dbf7cc52f9b096e0cd109a upstream. snd_seq_info_timer_read() reads the information of the timer assigned for each queue, but it's done in a racy way which may lead to UAF as spotted by syzkaller. This patch applies the missing q->timer_mutex lock while accessing the timer object as well as a slight code change to adapt the standard coding style. Reported-by: syzbot+2b2ef983f973e5c40943@syzkaller.appspotmail.com Cc: Link: https://lore.kernel.org/r/20200115203733.26530-1-tiwai@suse.de Signed-off-by: Takashi Iwai Signed-off-by: Greg Kroah-Hartman --- diff --git a/sound/core/seq/seq_timer.c b/sound/core/seq/seq_timer.c index b80985fbc334..0e1feb597586 100644 --- a/sound/core/seq/seq_timer.c +++ b/sound/core/seq/seq_timer.c @@ -479,15 +479,19 @@ void snd_seq_info_timer_read(struct snd_info_entry *entry, q = queueptr(idx); if (q == NULL) continue; - if ((tmr = q->timer) == NULL || - (ti = tmr->timeri) == NULL) { - queuefree(q); - continue; - } + mutex_lock(&q->timer_mutex); + tmr = q->timer; + if (!tmr) + goto unlock; + ti = tmr->timeri; + if (!ti) + goto unlock; snd_iprintf(buffer, "Timer for queue %i : %s\n", q->queue, ti->timer->name); resolution = snd_timer_resolution(ti) * tmr->ticks; snd_iprintf(buffer, " Period time : %lu.%09lu\n", resolution / 1000000000, resolution % 1000000000); snd_iprintf(buffer, " Skew : %u / %u\n", tmr->skew, tmr->skew_base); +unlock: + mutex_unlock(&q->timer_mutex); queuefree(q); } }