From fd95e68df6fe66344161a1329cbe5e5805e7b704 Mon Sep 17 00:00:00 2001 From: Takashi Iwai Date: Sat, 12 Sep 2026 18:21:42 +0200 Subject: ALSA: core: Fix potential UAF after asynchronous card release Usually a sound driver releases the resources assigned to the card via snd_card_free(), and it synchronizes with the whole release procedure. However, when the card is released asynchronously via snd_card_free_when_closed() like USB-audio driver, the situation is slightly different; although the snd_card_disconnect() call at the disconnection guarantees that any newer accesses will be gated, the in-flight tasks might be still accessing to the underlying card->dev device even after the disconnection, which would cause a use-after-free in the end, as reported by fuzzers. For addressing the bug above, this patch takes the refcount of card->dev at initialization of the card object, and releases at its destructor. This assures the availability of the card->dev in its whole lifecycle. Reported-by: Farhad Alemi Closes: https://lore.kernel.org/CA+0ovChexj4TrZL_2iG_P0WBEbZc5+73GfB3DkciQi=R8pZOnA@mail.gmail.com Closes: https://lore.kernel.org/CA+0ovCgQUQNN=Z1tJTouiCsDaXR5M-3-SQEGk-cpPXQkM5Xh+w@mail.gmail.com Cc: Link: https://patch.msgid.link/20260912162150.455144-1-tiwai@suse.de Signed-off-by: Takashi Iwai --- sound/core/init.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'sound/core') diff --git a/sound/core/init.c b/sound/core/init.c index 2f7f83a7611b..d05bea3c87f5 100644 --- a/sound/core/init.c +++ b/sound/core/init.c @@ -310,7 +310,7 @@ static int snd_card_init(struct snd_card *card, struct device *parent, kfree(card); /* manually free here, as no destructor called */ return err; } - card->dev = parent; + card->dev = get_device(parent); card->number = idx; WARN_ON(IS_MODULE(CONFIG_SND) && !module); card->module = module; @@ -603,6 +603,7 @@ static int snd_card_do_free(struct snd_card *card) dev_warn(card->dev, "unable to free card info\n"); /* Not fatal error */ } + put_device(card->dev); if (card->release_completion) complete(card->release_completion); if (!managed) -- cgit v1.2.3 From 1e713f9bb2ac583521f06b0eb4e22440b1e3d078 Mon Sep 17 00:00:00 2001 From: Nguyen Ngoc Thang Date: Sun, 13 Sep 2026 20:44:46 +0700 Subject: ALSA: pcm: set timer->private_data before registering the PCM timer snd_pcm_timer_init() calls snd_device_register() to link the new struct snd_timer into the global timer list while it still carries hw.c_resolution = snd_pcm_timer_resolution (and hw.start/hw.stop), and only afterwards sets timer->private_data = substream. Once the timer is on the list under register_mutex, a concurrent reader can already reach it through the same mutex and invoke these callbacks. /proc/asound/timers does this via c_resolution(), and snd_timer_open()+snd_timer_start() reach start()/stop() the same way. All three dereference timer->private_data, which for this brief window is NULL, giving a NULL-pointer dereference: substream = timer->private_data; return substream->runtime ? ... // substream is NULL Move the private_data/private_free assignment before snd_device_register() so the timer is never visible on the list without its private_data set. On the snd_device_register() failure path, private_free() (snd_pcm_timer_free()) can now run, but it only does substream->timer = NULL, which is already NULL at that point since substream->timer is set to the new timer just once, after a successful registration -- so the failure path stays safe. Reported-by: syzbot+19da64013c46df87f971@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=19da64013c46df87f971 Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Signed-off-by: Nguyen Ngoc Thang Link: https://patch.msgid.link/20260913134446.114724-1-ngocthang2710.1999@gmail.com Signed-off-by: Takashi Iwai --- sound/core/pcm_timer.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) (limited to 'sound/core') diff --git a/sound/core/pcm_timer.c b/sound/core/pcm_timer.c index ab0e5bd70f8f..18bedd66435d 100644 --- a/sound/core/pcm_timer.c +++ b/sound/core/pcm_timer.c @@ -111,12 +111,15 @@ void snd_pcm_timer_init(struct snd_pcm_substream *substream) snd_pcm_direction_name(substream->stream), tid.card, tid.device, tid.subdevice); timer->hw = snd_pcm_timer; + /* Set before registering: a concurrent reader can invoke our hw + * callbacks as soon as the timer is on the global list. + */ + timer->private_data = substream; + timer->private_free = snd_pcm_timer_free; if (snd_device_register(timer->card, timer) < 0) { snd_device_free(timer->card, timer); return; } - timer->private_data = substream; - timer->private_free = snd_pcm_timer_free; substream->timer = timer; } -- cgit v1.2.3