Re: [PATCH] drm/msm: Avoid potential overflow in timeout_to_jiffies()

[Dmitry Baryshkov <dmitry.baryshkov@linaro.org>]

On 17/09/2021 03:59, Marek Vasut wrote:
> The return type of ktime_divns() is s64. The timeout_to_jiffies() currently
> assigns the result of this ktime_divns() to unsigned long, which on 32 bit
> systems may overflow. Furthermore, the result of this function is sometimes
> also passed to functions which expect signed long, dma_fence_wait_timeout()
> is one such example.
> 
> Fix this by adjusting the type of remaining_jiffies to s64, so we do not
> suffer overflow there, and return a value limited to range of 0..INT_MAX,
> which is safe for all usecases of this timeout.
> 
> The above overflow can be triggered if userspace passes in too large timeout
> value, larger than INT_MAX / HZ seconds. The kernel detects it and complains
> about "schedule_timeout: wrong timeout value %lx" and generates a warning
> backtrace.
> 
> Note that this fixes commit 6cedb8b377bb ("drm/msm: avoid using 'timespec'"),
> because the previously used timespec_to_jiffies() function returned unsigned
> long instead of s64:
> static inline unsigned long timespec_to_jiffies(const struct timespec *value)
> 
> Fixes: 6cedb8b377bb ("drm/msm: avoid using 'timespec'")
> Signed-off-by: Marek Vasut <marex@denx.de>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Jordan Crouse <jcrouse@codeaurora.org>
> Cc: Rob Clark <robdclark@chromium.org>
> Cc: stable@vger.kernel.org # 5.6+

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>

> ---
> NOTE: This is related to Mesa MR
>        https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/12886
> ---
>   drivers/gpu/drm/msm/msm_drv.h | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/msm_drv.h b/drivers/gpu/drm/msm/msm_drv.h
> index 0b2686b060c73..d96b254b8aa46 100644
> --- a/drivers/gpu/drm/msm/msm_drv.h
> +++ b/drivers/gpu/drm/msm/msm_drv.h
> @@ -543,7 +543,7 @@ static inline int align_pitch(int width, int bpp)
>   static inline unsigned long timeout_to_jiffies(const ktime_t *timeout)
>   {
>   	ktime_t now = ktime_get();
> -	unsigned long remaining_jiffies;
> +	s64 remaining_jiffies;
>   
>   	if (ktime_compare(*timeout, now) < 0) {
>   		remaining_jiffies = 0;
> @@ -552,7 +552,7 @@ static inline unsigned long timeout_to_jiffies(const ktime_t *timeout)
>   		remaining_jiffies = ktime_divns(rem, NSEC_PER_SEC / HZ);
>   	}
>   
> -	return remaining_jiffies;
> +	return clamp(remaining_jiffies, 0LL, (s64)INT_MAX);
>   }
>   
>   #endif /* __MSM_DRV_H__ */
> 


-- 
With best wishes
Dmitry