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

[Arnd Bergmann]

On Fri, Sep 17, 2021 at 2:59 AM Marek Vasut <marex at denx.de> 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 at denx.de>
> Cc: Arnd Bergmann <arnd at arndb.de>
> Cc: Jordan Crouse <jcrouse at codeaurora.org>
> Cc: Rob Clark <robdclark at chromium.org>
> Cc: stable at vger.kernel.org # 5.6+
> ---

Acked-by: Arnd Bergmann <arnd at arndb.de>