linux-kernel - [PATCH v3] drm/i915: bounds check execbuffer relocation count

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Message-ID: <20130312003145.GA28993@www.outflux.net>
Date:	Mon, 11 Mar 2013 17:31:45 -0700
From:	Kees Cook <keescook@...omium.org>
To:	linux-kernel@...r.kernel.org
Cc:	Daniel Vetter <daniel.vetter@...ll.ch>,
	David Airlie <airlied@...ux.ie>,
	dri-devel@...ts.freedesktop.org, intel-gfx@...ts.freedesktop.org,
	Julien Tinnes <jln@...gle.com>, marcheu@...omium.org
Subject: [PATCH v3] drm/i915: bounds check execbuffer relocation count

It is possible to wrap the counter used to allocate the buffer for
relocation copies. This could lead to heap writing overflows.

CVE-2013-0913

v3: collapse test, improve comment
v2: move check into validate_exec_list

Signed-off-by: Kees Cook <keescook@...omium.org>
Reported-by: Pinkie Pie
Cc: stable@...r.kernel.org
---
 drivers/gpu/drm/i915/i915_gem_execbuffer.c |   11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
index b3a40ee..094ba41 100644
--- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
@@ -732,6 +732,8 @@ validate_exec_list(struct drm_i915_gem_exec_object2 *exec,
 		   int count)
 {
 	int i;
+	int relocs_total = 0;
+	int relocs_max = INT_MAX / sizeof(struct drm_i915_gem_relocation_entry);
 
 	for (i = 0; i < count; i++) {
 		char __user *ptr = (char __user *)(uintptr_t)exec[i].relocs_ptr;
@@ -740,10 +742,13 @@ validate_exec_list(struct drm_i915_gem_exec_object2 *exec,
 		if (exec[i].flags & __EXEC_OBJECT_UNKNOWN_FLAGS)
 			return -EINVAL;
 
-		/* First check for malicious input causing overflow */
-		if (exec[i].relocation_count >
-		    INT_MAX / sizeof(struct drm_i915_gem_relocation_entry))
+		/* First check for malicious input causing overflow in
+		 * the worst case where we need to allocate the entire
+		 * relocation tree as a single array.
+		 */
+		if (exec[i].relocation_count > relocs_max - relocs_total)
 			return -EINVAL;
+		relocs_total += exec[i].relocation_count;
 
 		length = exec[i].relocation_count *
 			sizeof(struct drm_i915_gem_relocation_entry);
-- 
1.7.9.5


-- 
Kees Cook
Chrome OS Security
--
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