From: Takashi Iwai tiwai@suse.de

stable inclusion from stable-v5.10.44 commit bd7d88b0874f82f7b29d1a53e574cedaf23166ba category: bugfix bugzilla: https://gitee.com/src-openeuler/kernel/issues/I9R4II CVE: CVE-2021-47281

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=...

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commit 83e197a8414c0ba545e7e3916ce05f836f349273 upstream.

The timer instance per queue is exclusive, and snd_seq_timer_open() should have managed the concurrent accesses. It looks as if it's checking the already existing timer instance at the beginning, but it's not right, because there is no protection, hence any later concurrent call of snd_seq_timer_open() may override the timer instance easily. This may result in UAF, as the leftover timer instance can keep running while the queue itself gets closed, as spotted by syzkaller recently.

For avoiding the race, add a proper check at the assignment of tmr->timeri again, and return -EBUSY if it's been already registered.

Reported-by: syzbot+ddc1260a83ed1cbf6fb5@syzkaller.appspotmail.com Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/000000000000dce34f05c42f110c@google.com Link: https://lore.kernel.org/r/20210610152059.24633-1-tiwai@suse.de Signed-off-by: Takashi Iwai tiwai@suse.de Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Chen Jun chenjun102@huawei.com Acked-by: Weilong Chen chenweilong@huawei.com Signed-off-by: Zheng Zengkai zhengzengkai@huawei.com

Conflicts: sound/core/seq/seq_timer.c [Some contexts different. No functional impact.] Signed-off-by: Zheng Zucheng zhengzucheng@huawei.com --- sound/core/seq/seq_timer.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/sound/core/seq/seq_timer.c b/sound/core/seq/seq_timer.c index f587d0e27476..168256b58313 100644 --- a/sound/core/seq/seq_timer.c +++ b/sound/core/seq/seq_timer.c @@ -308,8 +308,15 @@ int snd_seq_timer_open(struct snd_seq_queue *q) t->callback_data = q; t->flags |= SNDRV_TIMER_IFLG_AUTO; spin_lock_irq(&tmr->lock); - tmr->timeri = t; + if (tmr->timeri) + err = -EBUSY; + else + tmr->timeri = t; spin_unlock_irq(&tmr->lock); + if (err < 0) { + snd_timer_close(t); + return err; + } return 0; }