drm/i915: Avoid NULL deref in get_pages() unwind after error.

Fixes:
  http://bugzilla.kernel.org/show_bug.cgi?id=15527
  NULL pointer dereference in i915_gem_object_save_bit_17_swizzle

BUG: unable to handle kernel NULL pointer dereference at (null)
IP: [<f82b5d2b>] i915_gem_object_save_bit_17_swizzle+0x5b/0xc0 [i915]
Call Trace:
[<f82aea55>] ? i915_gem_object_put_pages+0x125/0x150 [i915]
[<f82aeb71>] ? i915_gem_object_get_pages+0xf1/0x110 [i915]
[<f82b0de8>] ? i915_gem_object_bind_to_gtt+0xb8/0x2a0 [i915]
[<c02db74d>] ? drm_mm_get_block_generic+0x4d/0x180
[<f82b11cd>] ? i915_gem_mmap_gtt_ioctl+0x16d/0x240 [i915]
[<f82ae786>] ? i915_gem_madvise_ioctl+0x86/0x120 [i915]

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reported-by: maciej.rutecki@gmail.com
Cc: stable@kernel.org
Reviewed-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Eric Anholt <eric@anholt.net>

1 files changed, 12 insertions, 9 deletions

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 134973f77069..933e865a8929 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1466,9 +1466,6 @@ i915_gem_object_put_pages(struct drm_gem_object *obj)
                 obj_priv->dirty = 0;
 
         for (i = 0; i < page_count; i++) {
-                if (obj_priv->pages[i] == NULL)
-                        break;
-
                 if (obj_priv->dirty)
                         set_page_dirty(obj_priv->pages[i]);
 
@@ -2251,7 +2248,6 @@ i915_gem_object_get_pages(struct drm_gem_object *obj,
         struct address_space *mapping;
         struct inode *inode;
         struct page *page;
-        int ret;
 
         if (obj_priv->pages_refcount++ != 0)
                 return 0;
@@ -2274,11 +2270,9 @@ i915_gem_object_get_pages(struct drm_gem_object *obj,
                                            mapping_gfp_mask (mapping) |
                                            __GFP_COLD |
                                            gfpmask);
-                if (IS_ERR(page)) {
-                        ret = PTR_ERR(page);
-                        i915_gem_object_put_pages(obj);
-                        return ret;
-                }
+                if (IS_ERR(page))
+                        goto err_pages;
+
                 obj_priv->pages[i] = page;
         }
 
@@ -2286,6 +2280,15 @@ i915_gem_object_get_pages(struct drm_gem_object *obj,
                 i915_gem_object_do_bit_17_swizzle(obj);
 
         return 0;
+
+err_pages:
+        while (i--)
+                page_cache_release(obj_priv->pages[i]);
+
+        drm_free_large(obj_priv->pages);
+        obj_priv->pages = NULL;
+        obj_priv->pages_refcount--;
+        return PTR_ERR(page);
 }
 
 static void sandybridge_write_fence_reg(struct drm_i915_fence_reg *reg)