linux-hardening - Re: [PATCH] media: v4l2-event: Annotate struct v4l2_subscribed_event with __counted

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Date: Sat, 23 Sep 2023 10:26:09 -0600
From: "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To: Kees Cook <keescook@...omium.org>,
 Mauro Carvalho Chehab <mchehab@...nel.org>
Cc: Hans Verkuil <hverkuil-cisco@...all.nl>, lijian <lijian@...ong.com>,
 linux-media@...r.kernel.org, Nathan Chancellor <nathan@...nel.org>,
 Nick Desaulniers <ndesaulniers@...gle.com>, Tom Rix <trix@...hat.com>,
 linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
 linux-hardening@...r.kernel.org
Subject: Re: [PATCH] media: v4l2-event: Annotate struct v4l2_subscribed_event
 with __counted_by



On 9/22/23 11:49, Kees Cook wrote:
> Prepare for the coming implementation by GCC and Clang of the __counted_by
> attribute. Flexible array members annotated with __counted_by can have
> their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS
> (for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
> functions).
> 
> As found with Coccinelle[1], add __counted_by for struct v4l2_subscribed_event.
> Additionally, since the element count member must be set before accessing
> the annotated flexible array member, move its initialization earlier.
> 
> [1] https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci
> 
> Cc: Mauro Carvalho Chehab <mchehab@...nel.org>
> Cc: Hans Verkuil <hverkuil-cisco@...all.nl>
> Cc: lijian <lijian@...ong.com>
> Cc: linux-media@...r.kernel.org
> Signed-off-by: Kees Cook <keescook@...omium.org>

Reviewed-by: Gustavo A. R. Silva <gustavoars@...nel.org>

Thanks
-- 
Gustavo

> ---
>   drivers/media/v4l2-core/v4l2-event.c | 2 +-
>   include/media/v4l2-event.h           | 2 +-
>   2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/media/v4l2-core/v4l2-event.c b/drivers/media/v4l2-core/v4l2-event.c
> index c5ce9f11ad7b..3898ff7edddb 100644
> --- a/drivers/media/v4l2-core/v4l2-event.c
> +++ b/drivers/media/v4l2-core/v4l2-event.c
> @@ -238,6 +238,7 @@ int v4l2_event_subscribe(struct v4l2_fh *fh,
>   	sev = kvzalloc(struct_size(sev, events, elems), GFP_KERNEL);
>   	if (!sev)
>   		return -ENOMEM;
> +	sev->elems = elems;
>   	for (i = 0; i < elems; i++)
>   		sev->events[i].sev = sev;
>   	sev->type = sub->type;
> @@ -245,7 +246,6 @@ int v4l2_event_subscribe(struct v4l2_fh *fh,
>   	sev->flags = sub->flags;
>   	sev->fh = fh;
>   	sev->ops = ops;
> -	sev->elems = elems;
>   
>   	mutex_lock(&fh->subscribe_lock);
>   
> diff --git a/include/media/v4l2-event.h b/include/media/v4l2-event.h
> index 4ffa914ade3a..3a0e2588361c 100644
> --- a/include/media/v4l2-event.h
> +++ b/include/media/v4l2-event.h
> @@ -78,7 +78,7 @@ struct v4l2_subscribed_event {
>   	unsigned int		elems;
>   	unsigned int		first;
>   	unsigned int		in_use;
> -	struct v4l2_kevent	events[];
> +	struct v4l2_kevent	events[] __counted_by(elems);
>   };
>   
>   /**