drm/i915: Sanity check mmap length against object size

We assumed that vm_mmap() would reject an attempt to mmap past the end of
the filp (our object), but we were wrong.

Applications that tried to use the mmap beyond the end of the object
would be greeted by a SIGBUS. After this patch, those applications will
be told about the error on creating the mmap, rather than at a random
moment on later access.

Reported-by: Antonio Argenziano <antonio.argenziano@intel.com>
Testcase: igt/gem_mmap/bad-size
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Antonio Argenziano <antonio.argenziano@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: stable@vger.kernel.org
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190314075829.16838-1-chris@chris-wilson.co.uk

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index b38c9531b5e8a4520981f9effdb157ef7dc8825c..b7086c8d472639b2f8de608d37a501b8643c2f19 100644 (file)
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1639,8 +1639,13 @@ i915_gem_mmap_ioctl(struct drm_device *dev, void *data,
         * pages from.
         */
        if (!obj->base.filp) {
-               i915_gem_object_put(obj);
-               return -ENXIO;
+               addr = -ENXIO;
+               goto err;
+       }
+
+       if (range_overflows(args->offset, args->size, (u64)obj->base.size)) {
+               addr = -EINVAL;
+               goto err;
        }
 
        addr = vm_mmap(obj->base.filp, 0, args->size,
@@ -1654,8 +1659,8 @@ i915_gem_mmap_ioctl(struct drm_device *dev, void *data,
                struct vm_area_struct *vma;
 
                if (down_write_killable(&mm->mmap_sem)) {
-                       i915_gem_object_put(obj);
-                       return -EINTR;
+                       addr = -EINTR;
+                       goto err;
                }
                vma = find_vma(mm, addr);
                if (vma && __vma_matches(vma, obj->base.filp, addr, args->size))
@@ -1673,12 +1678,10 @@ i915_gem_mmap_ioctl(struct drm_device *dev, void *data,
        i915_gem_object_put(obj);
 
        args->addr_ptr = (u64)addr;
-
        return 0;
 
 err:
        i915_gem_object_put(obj);
-
        return addr;
 }