[PATCH] drm/i915: Use copy_from_user() in fence copying

From: Kees Cook <keescook@chromium.org>
To: Jason Ekstrand <jason@jlekstrand.net>
Cc: Chris Wilson <chris@chris-wilson.co.uk>,
	intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
	linux-kernel@vger.kernel.org
Subject: [PATCH] drm/i915: Use copy_from_user() in fence copying
Date: Wed, 6 Dec 2017 12:28:50 -0800	[thread overview]
Message-ID: <20171206202850.GA38365@beast> (raw)

There's no good reason to separate the access_ok() from the copy,
especially since the access_ok() size is hard-coded instead of using
sizeof(). Instead, just use copy_from_user() directly.

Fixes: cf6e7bac6357 ("drm/i915: Add support for drm syncobjs")
Cc: Jason Ekstrand <jason@jlekstrand.net>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 drivers/gpu/drm/i915/i915_gem_execbuffer.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
index 435ed95df144..1da703213b17 100644
--- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
@@ -2087,8 +2087,6 @@ get_fence_array(struct drm_i915_gem_execbuffer2 *args,
 		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),
 				__GFP_NOWARN | GFP_KERNEL);
@@ -2099,7 +2097,7 @@ get_fence_array(struct drm_i915_gem_execbuffer2 *args,
 		struct drm_i915_gem_exec_fence fence;
 		struct drm_syncobj *syncobj;
 
-		if (__copy_from_user(&fence, user++, sizeof(fence))) {
+		if (copy_from_user(&fence, user++, sizeof(fence))) {
 			err = -EFAULT;
 			goto err;
 		}
-- 
2.7.4


-- 
Kees Cook
Pixel Security
