[Intel-gfx] [PATCH] drm/i915: Prevent overflow of execbuf.buffer_count and num_cliprects

[Chris Wilson]

We check whether the multiplies will overflow prior to calling
kmalloc_array so that we can respond with -EINVAL for the invalid user
arguments rather than treating it as an -ENOMEM that would otherwise
occur. However, as Dan Carpenter pointed out, we did an addition on the
unsigned int prior to passing to kmalloc_array where it would be
promoted to size_t for the calculation, thereby allowing it to overflow
and underallocate.

Reported-by: Dan Carpenter <dan.carpenter at oracle.com>
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---

I want to keep that check for reporting an attempted overflow as -EINVAL
so we can keep distinguishing rogue parameters from the excessively
large allocations. So we just need to do the promotion ourselves, right?
-Chris

---
 drivers/gpu/drm/i915/i915_gem_execbuffer.c | 30 ++++++++++++++++--------------
 1 file changed, 16 insertions(+), 14 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
index 8e8bc7aefd9c..2d69af40ab68 100644
--- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
@@ -2143,7 +2143,7 @@ static struct drm_syncobj **
 get_fence_array(struct drm_i915_gem_execbuffer2 *args,
 		struct drm_file *file)
 {
-	const unsigned int nfences = args->num_cliprects;
+	const size_t nfences = args->num_cliprects;
 	struct drm_i915_gem_exec_fence __user *user;
 	struct drm_syncobj **fences;
 	unsigned int n;
@@ -2152,14 +2152,14 @@ get_fence_array(struct drm_i915_gem_execbuffer2 *args,
 	if (!(args->flags & I915_EXEC_FENCE_ARRAY))
 		return NULL;
 
-	if (nfences > SIZE_MAX / sizeof(*fences))
+	if (nfences > SIZE_MAX / max(sizeof(*fences), 2*sizeof(u32)))
 		return ERR_PTR(-EINVAL);
 
 	user = u64_to_user_ptr(args->cliprects_ptr);
 	if (!access_ok(VERIFY_READ, user, nfences * 2 * sizeof(u32)))
 		return ERR_PTR(-EFAULT);
 
-	fences = kvmalloc_array(args->num_cliprects, sizeof(*fences),
+	fences = kvmalloc_array(nfences, sizeof(*fences),
 				__GFP_NOWARN | GFP_TEMPORARY);
 	if (!fences)
 		return ERR_PTR(-ENOMEM);
@@ -2517,10 +2517,11 @@ i915_gem_execbuffer(struct drm_device *dev, void *data,
 	struct drm_i915_gem_execbuffer2 exec2;
 	struct drm_i915_gem_exec_object *exec_list = NULL;
 	struct drm_i915_gem_exec_object2 *exec2_list = NULL;
+	const size_t count = args->buffer_count;
 	unsigned int i;
 	int err;
 
-	if (args->buffer_count < 1 || args->buffer_count > SIZE_MAX / sz - 1) {
+	if (count < 1 || count > SIZE_MAX / sz - 1) {
 		DRM_DEBUG("execbuf2 with %d buffers\n", args->buffer_count);
 		return -EINVAL;
 	}
@@ -2540,9 +2541,9 @@ i915_gem_execbuffer(struct drm_device *dev, void *data,
 		return -EINVAL;
 
 	/* Copy in the exec list from userland */
-	exec_list = kvmalloc_array(args->buffer_count, sizeof(*exec_list),
+	exec_list = kvmalloc_array(count, sizeof(*exec_list),
 				   __GFP_NOWARN | GFP_TEMPORARY);
-	exec2_list = kvmalloc_array(args->buffer_count + 1, sz,
+	exec2_list = kvmalloc_array(count + 1, sz,
 				    __GFP_NOWARN | GFP_TEMPORARY);
 	if (exec_list == NULL || exec2_list == NULL) {
 		DRM_DEBUG("Failed to allocate exec list for %d buffers\n",
@@ -2553,7 +2554,7 @@ i915_gem_execbuffer(struct drm_device *dev, void *data,
 	}
 	err = copy_from_user(exec_list,
 			     u64_to_user_ptr(args->buffers_ptr),
-			     sizeof(*exec_list) * args->buffer_count);
+			     sizeof(*exec_list) * count);
 	if (err) {
 		DRM_DEBUG("copy %d exec entries failed %d\n",
 			  args->buffer_count, err);
@@ -2607,10 +2608,11 @@ i915_gem_execbuffer2(struct drm_device *dev, void *data,
 	struct drm_i915_gem_execbuffer2 *args = data;
 	struct drm_i915_gem_exec_object2 *exec2_list;
 	struct drm_syncobj **fences = NULL;
+	const size_t count = args->buffer_count;
 	int err;
 
-	if (args->buffer_count < 1 || args->buffer_count > SIZE_MAX / sz - 1) {
-		DRM_DEBUG("execbuf2 with %d buffers\n", args->buffer_count);
+	if (count < 1 || count > SIZE_MAX / sz - 1) {
+		DRM_DEBUG("execbuf2 with %zd buffers\n", count);
 		return -EINVAL;
 	}
 
@@ -2618,17 +2620,17 @@ i915_gem_execbuffer2(struct drm_device *dev, void *data,
 		return -EINVAL;
 
 	/* Allocate an extra slot for use by the command parser */
-	exec2_list = kvmalloc_array(args->buffer_count + 1, sz,
+	exec2_list = kvmalloc_array(count + 1, sz,
 				    __GFP_NOWARN | GFP_TEMPORARY);
 	if (exec2_list == NULL) {
-		DRM_DEBUG("Failed to allocate exec list for %d buffers\n",
-			  args->buffer_count);
+		DRM_DEBUG("Failed to allocate exec list for %zd buffers\n",
+			  count);
 		return -ENOMEM;
 	}
 	if (copy_from_user(exec2_list,
 			   u64_to_user_ptr(args->buffers_ptr),
-			   sizeof(*exec2_list) * args->buffer_count)) {
-		DRM_DEBUG("copy %d exec entries failed\n", args->buffer_count);
+			   sizeof(*exec2_list) * count)) {
+		DRM_DEBUG("copy %zd exec entries failed\n", count);
 		kvfree(exec2_list);
 		return -EFAULT;
 	}
-- 
2.14.1