[PATCH v2] drm/i915: bounds check execbuffer relocation count

[Kees Cook <keescook@chromium.org>]

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

Signed-off-by: Kees Cook <keescook@chromium.org>
Reported-by: Pinkie Pie
Cc: stable@vger.kernel.org
---
v2:
 - move check into validate_exec_list
---
 drivers/gpu/drm/i915/i915_gem_execbuffer.c |    4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
index 752e399..72d7841 100644
--- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
@@ -732,6 +732,7 @@ validate_exec_list(struct drm_i915_gem_exec_object2 *exec,
 		   int count)
 {
 	int i;
+	int total = 0;
 
 	for (i = 0; i < count; i++) {
 		char __user *ptr = (char __user *)(uintptr_t)exec[i].relocs_ptr;
@@ -744,6 +745,9 @@ validate_exec_list(struct drm_i915_gem_exec_object2 *exec,
 		if (exec[i].relocation_count >
 		    INT_MAX / sizeof(struct drm_i915_gem_relocation_entry))
 			return -EINVAL;
+		if (exec[i].relocation_count > INT_MAX - total)
+			return -ENOMEM;
+		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