Re: [PATCH] media: media-request: Fix crash if memory allocation fails

[Sakari Ailus]

On Sun, Jun 21, 2020 at 02:30:40PM +0300, Tuomas Tynkkynen wrote:
> Syzbot reports a NULL-ptr deref in the kref_put() call:
> 
> BUG: KASAN: null-ptr-deref in media_request_put drivers/media/mc/mc-request.c:81 [inline]
>  kref_put include/linux/kref.h:64 [inline]
>  media_request_put drivers/media/mc/mc-request.c:81 [inline]
>  media_request_close+0x4d/0x170 drivers/media/mc/mc-request.c:89
>  __fput+0x2ed/0x750 fs/file_table.c:281
>  task_work_run+0x147/0x1d0 kernel/task_work.c:123
>  tracehook_notify_resume include/linux/tracehook.h:188 [inline]
>  exit_to_usermode_loop arch/x86/entry/common.c:165 [inline]
>  prepare_exit_to_usermode+0x48e/0x600 arch/x86/entry/common.c:196
> 
> What led to this crash was an injected memory allocation failure in
> media_request_alloc():
> 
> FAULT_INJECTION: forcing a failure.
> name failslab, interval 1, probability 0, space 0, times 0
>  should_failslab+0x5/0x20
>  kmem_cache_alloc_trace+0x57/0x300
>  ? anon_inode_getfile+0xe5/0x170
>  media_request_alloc+0x339/0x440
>  media_device_request_alloc+0x94/0xc0
>  media_device_ioctl+0x1fb/0x330
>  ? do_vfs_ioctl+0x6ea/0x1a00
>  ? media_ioctl+0x101/0x120
>  ? __media_device_usb_init+0x430/0x430
>  ? media_poll+0x110/0x110
>  __se_sys_ioctl+0xf9/0x160
>  do_syscall_64+0xf3/0x1b0
> 
> When that allocation fails, filp->private_data is left uninitialized
> which media_request_close() does not expect and crashes.
> 
> To avoid this, reorder media_request_alloc() such that
> allocating the struct file happens as the last step thus
> media_request_close() will no longer get called for a partially created
> media request.
> 
> Reported-by: syzbot+6bed2d543cf7e48b822b@xxxxxxxxxxxxxxxxxxxxxxxxx
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Tuomas Tynkkynen <tuomas.tynkkynen@xxxxxx>

Thanks a lot!

I'm adding this tag:

Fixes: 10905d70d788 ("media: media-request: implement media requests")

FYI: in the future, to get patches to the stable trees, please do add the
Cc: stable... tag, but not actually send the patch to stable@vger e-mail
address.

-- 
Kind regards,

Sakari Ailus