linux-kernel - [PATCH] drm/i915/gt: Prevent possible NULL dereference in __caps

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Date: Tue, 6 Feb 2024 08:45:43 -0800
From: Nikita Zhandarovich <n.zhandarovich@...tech.ru>
To: Jani Nikula <jani.nikula@...ux.intel.com>
CC: Nikita Zhandarovich <n.zhandarovich@...tech.ru>, Joonas Lahtinen
	<joonas.lahtinen@...ux.intel.com>, Rodrigo Vivi <rodrigo.vivi@...el.com>,
	Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>, David Airlie
	<airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>,
	<intel-gfx@...ts.freedesktop.org>, <dri-devel@...ts.freedesktop.org>,
	<linux-kernel@...r.kernel.org>, <lvc-project@...uxtesting.org>
Subject: [PATCH] drm/i915/gt: Prevent possible NULL dereference in __caps_show()

After falling through the switch statement to default case 'repr' is
initialized with NULL, which will lead to incorrect dereference of
'!repr[n]' in the following loop.

Fix it with the help of an additional check for NULL.

Found by Linux Verification Center (linuxtesting.org) with static
analysis tool SVACE.

Fixes: 4ec76dbeb62b ("drm/i915/gt: Expose engine properties via sysfs")
Signed-off-by: Nikita Zhandarovich <n.zhandarovich@...tech.ru>
---
P.S. The NULL-deref problem might be dealt with this way but I am
not certain that the rest of the __caps_show() behaviour remains
correct if we end up in default case. For instance, as far as I
can tell, buf might turn out to be w/o '\0'. I could use some
direction if this has to be addressed as well.

 drivers/gpu/drm/i915/gt/sysfs_engines.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/gt/sysfs_engines.c b/drivers/gpu/drm/i915/gt/sysfs_engines.c
index 021f51d9b456..6b130b732867 100644
--- a/drivers/gpu/drm/i915/gt/sysfs_engines.c
+++ b/drivers/gpu/drm/i915/gt/sysfs_engines.c
@@ -105,7 +105,7 @@ __caps_show(struct intel_engine_cs *engine,
 
 	len = 0;
 	for_each_set_bit(n, &caps, show_unknown ? BITS_PER_LONG : count) {
-		if (n >= count || !repr[n]) {
+		if (n >= count || !repr || !repr[n]) {
 			if (GEM_WARN_ON(show_unknown))
 				len += sysfs_emit_at(buf, len, "[%x] ", n);
 		} else {
-- 
2.25.1