Re: [PATCH] usb: gadget: uvc: Fix argument to sizeof() in uvc_register_video()

[Kees Cook <keescook@chromium.org>]

On Wed, Sep 28, 2022 at 01:19:21PM -0700, Nathan Chancellor wrote:
> When building s390 allmodconfig after commit 9b91a6523078 ("usb: gadget:
> uvc: increase worker prio to WQ_HIGHPRI"), the following error occurs:
> 
>   In file included from ../include/linux/string.h:253,
>                    from ../include/linux/bitmap.h:11,
>                    from ../include/linux/cpumask.h:12,
>                    from ../include/linux/smp.h:13,
>                    from ../include/linux/lockdep.h:14,
>                    from ../include/linux/rcupdate.h:29,
>                    from ../include/linux/rculist.h:11,
>                    from ../include/linux/pid.h:5,
>                    from ../include/linux/sched.h:14,
>                    from ../include/linux/ratelimit.h:6,
>                    from ../include/linux/dev_printk.h:16,
>                    from ../include/linux/device.h:15,
>                    from ../drivers/usb/gadget/function/f_uvc.c:9:
>   In function ‘fortify_memset_chk’,
>       inlined from ‘uvc_register_video’ at ../drivers/usb/gadget/function/f_uvc.c:424:2:
>   ../include/linux/fortify-string.h:301:25: error: call to ‘__write_overflow_field’ declared with attribute warning: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Werror=attribute-warning]
>     301 |                         __write_overflow_field(p_size_field, size);
>         |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> This points to the memset() in uvc_register_video(). It is clear that
> the argument to sizeof() is incorrect, as uvc->vdev (a 'struct
> video_device') is being zeroed out but the size of uvc->video (a 'struct
> uvc_video') is being used as the third arugment to memset().
> 
> pahole shows that prior to commit 9b91a6523078 ("usb: gadget: uvc:
> increase worker prio to WQ_HIGHPRI"), 'struct video_device' and
> 'struct ucv_video' had the same size, meaning that the argument to
> sizeof() is incorrect semantically but there is no visible issue:
> 
>   $ pahole -s build/drivers/usb/gadget/function/f_uvc.o | grep -E "(uvc_video|video_device)\s+"
>   video_device    1400    4
>   uvc_video       1400    3
> 
> After that change, uvc_video becomes slightly larger, meaning that the
> memset() will overwrite by 8 bytes:
> 
>   $ pahole -s build/drivers/usb/gadget/function/f_uvc.o | grep -E "(uvc_video|video_device)\s+"
>   video_device    1400    4
>   uvc_video       1408    3
> 
> Fix the arugment to sizeof() so that there is no overwrite.
> 
> Cc: stable@vger.kernel.org
> Fixes: e4ce9ed835bc ("usb: gadget: uvc: ensure the vdev is unset")
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>

Thanks for tracking that down!

Reviewed-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook