linux-kernel - [PATCH 5.14 029/151] drm/msm: Avoid potential overflow in timeout_to

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Date:   Mon, 18 Oct 2021 15:23:28 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Marek Vasut <marex@...x.de>,
        Arnd Bergmann <arnd@...db.de>,
        Jordan Crouse <jcrouse@...eaurora.org>,
        Rob Clark <robdclark@...omium.org>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Subject: [PATCH 5.14 029/151] drm/msm: Avoid potential overflow in timeout_to_jiffies()

From: Marek Vasut <marex@...x.de>

commit 171316a68d9a8e0d9e28b7cf4c15afc4c6244a4e upstream.

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@...x.de>
Cc: Arnd Bergmann <arnd@...db.de>
Cc: Jordan Crouse <jcrouse@...eaurora.org>
Cc: Rob Clark <robdclark@...omium.org>
Cc: stable@...r.kernel.org # 5.6+
Acked-by: Arnd Bergmann <arnd@...db.de>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Link: https://lore.kernel.org/r/20210917005913.157379-1-marex@denx.de
Signed-off-by: Rob Clark <robdclark@...omium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/gpu/drm/msm/msm_drv.h |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/gpu/drm/msm/msm_drv.h
+++ b/drivers/gpu/drm/msm/msm_drv.h
@@ -535,7 +535,7 @@ static inline int align_pitch(int width,
 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;
@@ -544,7 +544,7 @@ static inline unsigned long timeout_to_j
 		remaining_jiffies = ktime_divns(rem, NSEC_PER_SEC / HZ);
 	}
 
-	return remaining_jiffies;
+	return clamp(remaining_jiffies, 0LL, (s64)INT_MAX);
 }
 
 #endif /* __MSM_DRV_H__ */