Re: [PATCH] [media] sound/usb: fix NULL dereference in usb_audio_probe()

[Shuah Khan]

On 03/15/2016 06:35 AM, Nicolai Stange wrote:
> With commit
> 
>   aebb2b89bff0 ("[media] sound/usb: Use Media Controller API to share
>                  media resources")
> 
> an access to quirk->media_device without checking for quirk != NULL has
> been introduced in usb_audio_probe().
> 
> With a Plantronics USB headset (device ID 0x047f:0xc010) attached,
> this results in the following splat at boot time:
> 
>   BUG: unable to handle kernel NULL pointer dereference at 0000000000000014
>   IP: [<ffffffffa089aa6c>] usb_audio_probe+0x2cc/0x9a0 [snd_usb_audio]
>   Oops: 0000 [#1] SMP
>   [...]
>   CPU: 2 PID: 696 Comm: systemd-udevd Not tainted 4.5.0-next-20160315 #13
>   Hardware name: Dell Inc. Latitude E6540/0725FP, BIOS A10 06/26/2014
>   task: ffff88021c88d7c0 ti: ffff88003d5b0000 task.ti: ffff88003d5b0000
>   RIP: 0010:[<ffffffffa089aa6c>]  [<ffffffffa089aa6c>]
>                                 usb_audio_probe+0x2cc/0x9a0 [snd_usb_audio]
>   [...]
>   Call Trace:
>    [<ffffffff815a8e16>] usb_probe_interface+0x136/0x2d0
>    [<ffffffff81509edc>] driver_probe_device+0x22c/0x440
>    [<ffffffff8150a1c1>] __driver_attach+0xd1/0xf0
>    [<ffffffff8150a0f0>] ? driver_probe_device+0x440/0x440
>    [<ffffffff815077ec>] bus_for_each_dev+0x6c/0xc0
>    [<ffffffff815095ce>] driver_attach+0x1e/0x20
>    [<ffffffff81509013>] bus_add_driver+0x1c3/0x280
>    [<ffffffff8150ab10>] driver_register+0x60/0xe0
>    [<ffffffff815a7711>] usb_register_driver+0x81/0x140
>    [<ffffffffa08c7000>] ? 0xffffffffa08c7000
>    [<ffffffffa08c701e>] usb_audio_driver_init+0x1e/0x1000 [snd_usb_audio]
>    [<ffffffff81002123>] do_one_initcall+0xb3/0x1f0
>    [<ffffffff811fb091>] ? __vunmap+0x81/0xd0
>    [<ffffffff8121b8d2>] ? kmem_cache_alloc_trace+0x182/0x1d0
>    [<ffffffff811b0267>] ? do_init_module+0x27/0x1d8
>    [<ffffffff811b029f>] do_init_module+0x5f/0x1d8
>    [<ffffffff8112ce35>] load_module+0x1fe5/0x27a0
>    [<ffffffff81129870>] ? __symbol_put+0x60/0x60
>    [<ffffffff81241690>] ? vfs_read+0x110/0x130
>    [<ffffffff8112d866>] SYSC_finit_module+0xe6/0x120
>    [<ffffffff8112d8be>] SyS_finit_module+0xe/0x10
>    [<ffffffff81003d94>] do_syscall_64+0x64/0x110
>    [<ffffffff817c0b61>] entry_SYSCALL64_slow_path+0x25/0x25
> 
> After encountering this, the system-udevd process seems to be blocked
> until it is killed when hitting its timeout of 3min.
> 
> In analogy to the other accesses to members of quirk in usb_audio_probe(),
> check for quirk != NULL before accessing its ->media_device.
> 
> Fixes: aebb2b89bff0 ("[media] sound/usb: Use Media Controller API to share
>                       media resources")
> Signed-off-by: Nicolai Stange <nicstange@xxxxxxxxx>
> ---
>  Applicable to linux-next-20160315.
> 
>  sound/usb/card.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/sound/usb/card.c b/sound/usb/card.c
> index 63244bb..479621e 100644
> --- a/sound/usb/card.c
> +++ b/sound/usb/card.c
> @@ -612,7 +612,7 @@ static int usb_audio_probe(struct usb_interface *intf,
>  	if (err < 0)
>  		goto __error;
>  
> -	if (quirk->media_device) {
> +	if (quirk && quirk->media_device) {
>  		/* don't want to fail when media_snd_device_create() fails */
>  		media_snd_device_create(chip, intf);
>  	}
> 

Thanks for finding the problem and fixing it.

Reviewed-by: Shuah Khan <shuahkh@xxxxxxxxxxxxxxx>

-- Shuah

-- 
Shuah Khan
Sr. Linux Kernel Developer
Open Source Innovation Group
Samsung Research America (Silicon Valley)
shuahkh@xxxxxxxxxxxxxxx | (970) 217-8978