drm/prime: Always add exported buffers to the handle cache

... not only when the dma-buf is freshly created. In contrived
examples someone else could have exported/imported the dma-buf already
and handed us the gem object with a flink name. If such on object gets
reexported as a dma_buf we won't have it in the handle cache already,
which breaks the guarantee that for dma-buf imports we always hand
back an existing handle if there is one.

This is exercised by igt/prime_self_import/with_one_bo_two_files

Now if we extend the locked sections just a notch more we can also
plug th racy buf/handle cache setup in handle_to_fd:

If evil userspace races a concurrent gem close against a prime export
operation we can end up tearing down the gem handle before the dma buf
handle cache is set up. When handle_to_fd gets around to adding the
handle to the cache there will be no one left to clean it up,
effectily leaking the bo (and the dma-buf, since the handle cache
holds a ref on the dma-buf):

Thread A			Thread B

handle_to_fd:

lookup gem object from handle
creates new dma_buf

				gem_close on the same handle
				obj->dma_buf is set, but file priv buf
				handle cache has no entry

				obj->handle_count drops to 0

drm_prime_add_buf_handle sets up the handle cache

-> We have a dma-buf reference in the handle cache, but since the
handle_count of the gem object already dropped to 0 no on will clean
it up. When closing the drm device fd we'll hit the WARN_ON in
drm_prime_destroy_file_private.

The important change is to extend the critical section of the
filp->prime.lock to cover the gem handle lookup. This serializes with
a concurrent gem handle close.

This leak is exercised by igt/prime_self_import/export-vs-gem_close-race

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Dave Airlie <airlied@redhat.com>
This commit is contained in:
Daniel Vetter 2013-08-15 00:02:49 +02:00 коммит произвёл Dave Airlie
Родитель de9564d8b9
Коммит d0b2c5334f
3 изменённых файлов: 53 добавлений и 36 удалений

Просмотреть файл

@ -195,10 +195,12 @@ drm_gem_remove_prime_handles(struct drm_gem_object *obj, struct drm_file *filp)
* Note: obj->dma_buf can't disappear as long as we still hold a
* handle reference in obj->handle_count.
*/
mutex_lock(&filp->prime.lock);
if (obj->dma_buf) {
drm_prime_remove_buf_handle(&filp->prime,
obj->dma_buf);
drm_prime_remove_buf_handle_locked(&filp->prime,
obj->dma_buf);
}
mutex_unlock(&filp->prime.lock);
}
static void drm_gem_object_ref_bug(struct kref *list_kref)

Просмотреть файл

@ -83,6 +83,19 @@ static int drm_prime_add_buf_handle(struct drm_prime_file_private *prime_fpriv,
return 0;
}
static struct dma_buf *drm_prime_lookup_buf_by_handle(struct drm_prime_file_private *prime_fpriv,
uint32_t handle)
{
struct drm_prime_member *member;
list_for_each_entry(member, &prime_fpriv->head, entry) {
if (member->handle == handle)
return member->dma_buf;
}
return NULL;
}
static int drm_prime_lookup_buf_handle(struct drm_prime_file_private *prime_fpriv,
struct dma_buf *dma_buf,
uint32_t *handle)
@ -146,9 +159,8 @@ static void drm_gem_map_detach(struct dma_buf *dma_buf,
attach->priv = NULL;
}
static void drm_prime_remove_buf_handle_locked(
struct drm_prime_file_private *prime_fpriv,
struct dma_buf *dma_buf)
void drm_prime_remove_buf_handle_locked(struct drm_prime_file_private *prime_fpriv,
struct dma_buf *dma_buf)
{
struct drm_prime_member *member, *safe;
@ -337,6 +349,8 @@ static struct dma_buf *export_and_register_object(struct drm_device *dev,
*/
obj->dma_buf = dmabuf;
get_dma_buf(obj->dma_buf);
/* Grab a new ref since the callers is now used by the dma-buf */
drm_gem_object_reference(obj);
return dmabuf;
}
@ -349,10 +363,20 @@ int drm_gem_prime_handle_to_fd(struct drm_device *dev,
int ret = 0;
struct dma_buf *dmabuf;
mutex_lock(&file_priv->prime.lock);
obj = drm_gem_object_lookup(dev, file_priv, handle);
if (!obj)
return -ENOENT;
if (!obj) {
ret = -ENOENT;
goto out_unlock;
}
dmabuf = drm_prime_lookup_buf_by_handle(&file_priv->prime, handle);
if (dmabuf) {
get_dma_buf(dmabuf);
goto out_have_handle;
}
mutex_lock(&dev->object_name_lock);
/* re-export the original imported object */
if (obj->import_attach) {
dmabuf = obj->import_attach->dmabuf;
@ -360,45 +384,45 @@ int drm_gem_prime_handle_to_fd(struct drm_device *dev,
goto out_have_obj;
}
mutex_lock(&dev->object_name_lock);
if (obj->dma_buf) {
get_dma_buf(obj->dma_buf);
dmabuf = obj->dma_buf;
mutex_unlock(&dev->object_name_lock);
goto out_have_obj;
}
dmabuf = export_and_register_object(dev, obj, flags);
mutex_unlock(&dev->object_name_lock);
if (IS_ERR(dmabuf)) {
/* normally the created dma-buf takes ownership of the ref,
* but if that fails then drop the ref
*/
ret = PTR_ERR(dmabuf);
mutex_unlock(&dev->object_name_lock);
goto out;
}
mutex_lock(&file_priv->prime.lock);
/* if we've exported this buffer the cheat and add it to the import list
* so we get the correct handle back
out_have_obj:
/*
* If we've exported this buffer then cheat and add it to the import list
* so we get the correct handle back. We must do this under the
* protection of dev->object_name_lock to ensure that a racing gem close
* ioctl doesn't miss to remove this buffer handle from the cache.
*/
ret = drm_prime_add_buf_handle(&file_priv->prime,
dmabuf, handle);
mutex_unlock(&dev->object_name_lock);
if (ret)
goto fail_put_dmabuf;
out_have_handle:
ret = dma_buf_fd(dmabuf, flags);
if (ret < 0)
goto fail_rm_handle;
*prime_fd = ret;
mutex_unlock(&file_priv->prime.lock);
return 0;
out_have_obj:
ret = dma_buf_fd(dmabuf, flags);
/*
* We must _not_ remove the buffer from the handle cache since the newly
* created dma buf is already linked in the global obj->dma_buf pointer,
* and that is invariant as long as a userspace gem handle exists.
* Closing the handle will clean out the cache anyway, so we don't leak.
*/
if (ret < 0) {
dma_buf_put(dmabuf);
goto fail_put_dmabuf;
} else {
*prime_fd = ret;
ret = 0;
@ -406,14 +430,13 @@ out_have_obj:
goto out;
fail_rm_handle:
drm_prime_remove_buf_handle_locked(&file_priv->prime,
dmabuf);
mutex_unlock(&file_priv->prime.lock);
fail_put_dmabuf:
dma_buf_put(dmabuf);
out:
drm_gem_object_unreference_unlocked(obj);
out_unlock:
mutex_unlock(&file_priv->prime.lock);
return ret;
}
EXPORT_SYMBOL(drm_gem_prime_handle_to_fd);
@ -669,11 +692,3 @@ void drm_prime_destroy_file_private(struct drm_prime_file_private *prime_fpriv)
WARN_ON(!list_empty(&prime_fpriv->head));
}
EXPORT_SYMBOL(drm_prime_destroy_file_private);
void drm_prime_remove_buf_handle(struct drm_prime_file_private *prime_fpriv, struct dma_buf *dma_buf)
{
mutex_lock(&prime_fpriv->lock);
drm_prime_remove_buf_handle_locked(prime_fpriv, dma_buf);
mutex_unlock(&prime_fpriv->lock);
}
EXPORT_SYMBOL(drm_prime_remove_buf_handle);

Просмотреть файл

@ -1508,7 +1508,7 @@ int drm_gem_dumb_destroy(struct drm_file *file,
void drm_prime_init_file_private(struct drm_prime_file_private *prime_fpriv);
void drm_prime_destroy_file_private(struct drm_prime_file_private *prime_fpriv);
void drm_prime_remove_buf_handle(struct drm_prime_file_private *prime_fpriv, struct dma_buf *dma_buf);
void drm_prime_remove_buf_handle_locked(struct drm_prime_file_private *prime_fpriv, struct dma_buf *dma_buf);
#if DRM_DEBUG_CODE
extern int drm_vma_info(struct seq_file *m, void *data);