From 6ff1a25318ebf688ef9593fe09cd449f6fb4ad31 Mon Sep 17 00:00:00 2001 From: Takashi Iwai Date: Mon, 14 Nov 2016 21:46:47 +0100 Subject: [PATCH] ALSA: usb-audio: Fix use-after-free of usb_device at disconnect The usb-audio driver implements the deferred device disconnection for the device in use. In this mode, the disconnection callback returns immediately while the actual ALSA card object removal happens later when all files get closed. As Shuah reported, this code flow, however, leads to a use-after-free, detected by KASAN: BUG: KASAN: use-after-free in snd_usb_audio_free+0x134/0x160 [snd_usb_audio] at addr ffff8801c863ce10 Write of size 8 by task pulseaudio/2244 Call Trace: [] dump_stack+0x67/0x94 [] kasan_object_err+0x21/0x70 [] kasan_report_error+0x1fa/0x4e0 [] ? kasan_slab_free+0x87/0xb0 [] __asan_report_store8_noabort+0x43/0x50 [] ? snd_usb_audio_free+0x134/0x160 [snd_usb_audio] [] snd_usb_audio_free+0x134/0x160 [snd_usb_audio] [] snd_usb_audio_dev_free+0x31/0x40 [snd_usb_audio] [] __snd_device_free+0x12a/0x210 [] snd_device_free_all+0x85/0xd0 [] release_card_device+0x34/0x130 [] device_release+0x76/0x1e0 [] kobject_release+0x107/0x370 ..... Object at ffff8801c863cc80, in cache kmalloc-2048 size: 2048 Allocated: [] save_stack_trace+0x2b/0x50 [] save_stack+0x46/0xd0 [] kasan_kmalloc+0xad/0xe0 [] kmem_cache_alloc_trace+0xfa/0x240 [] usb_alloc_dev+0x57/0xc90 [] hub_event+0xf1d/0x35f0 .... Freed: [] save_stack_trace+0x2b/0x50 [] save_stack+0x46/0xd0 [] kasan_slab_free+0x71/0xb0 [] kfree+0xd9/0x280 [] usb_release_dev+0xde/0x110 [] device_release+0x76/0x1e0 .... It's the code trying to clear drvdata of the assigned usb_device where the usb_device itself was already released in usb_release_dev() after the disconnect callback. This patch fixes it by checking whether the code path is via the disconnect callback, i.e. chip->shutdown flag is set. Fixes: 79289e24194a ('ALSA: usb-audio: Refer to chip->usb_id for quirks...') Reported-and-tested-by: Shuah Khan Cc: # v4.6+ Signed-off-by: Takashi Iwai --- sound/usb/card.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/sound/usb/card.c b/sound/usb/card.c index 9e5276d6dda0..2ddc034673a8 100644 --- a/sound/usb/card.c +++ b/sound/usb/card.c @@ -315,7 +315,8 @@ static int snd_usb_audio_free(struct snd_usb_audio *chip) snd_usb_endpoint_free(ep); mutex_destroy(&chip->mutex); - dev_set_drvdata(&chip->dev->dev, NULL); + if (!atomic_read(&chip->shutdown)) + dev_set_drvdata(&chip->dev->dev, NULL); kfree(chip); return 0; }