On Tue, Dec 19, 2017 at 12:07:00PM +0000, Chris Wilson wrote:
> The vk cts test:
> dEQP-VK.api.external.semaphore.opaque_fd.export_multiple_times_temporary
>
> triggers a lot of
> VFS: Close: file count is 0
>
> Dave pointed out that clearing the syncobj->file from
> drm_syncobj_file_release() was sufficient to silence the test, but that
> opens a can of worm since we assumed that the syncobj->file was never
> unset. Stop trying to reuse the same struct file for every fd pointing
> to the drm_syncobj, and allocate one file for each fd instead.
It's worse: syncobj->file points to a refcounted thing, and we never did
grab a reference for it. This is a classic use-after-free thing :-)
> Reported-by: Dave Airlie <airlied@xxxxxxxxxx>
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Dave Airlie <airlied@xxxxxxxxxx>
Assuming it doesn't break the vk testsuite:
Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
Also an igt for this would be nice:
1. create syncobj
2. export to fd
3. close fd, note that now syncobj->file points to a freed struct file
4. reexport -> BOOM
Cheers, Daniel
> ---
> drivers/gpu/drm/drm_syncobj.c | 74 +++++++++++++++----------------------------
> include/drm/drm_syncobj.h | 4 ---
> 2 files changed, 26 insertions(+), 52 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c
> index 131695915acd..0cca2e792719 100644
> --- a/drivers/gpu/drm/drm_syncobj.c
> +++ b/drivers/gpu/drm/drm_syncobj.c
> @@ -399,23 +399,6 @@ static const struct file_operations drm_syncobj_file_fops = {
> .release = drm_syncobj_file_release,
> };
>
> -static int drm_syncobj_alloc_file(struct drm_syncobj *syncobj)
> -{
> - struct file *file = anon_inode_getfile("syncobj_file",
> - &drm_syncobj_file_fops,
> - syncobj, 0);
> - if (IS_ERR(file))
> - return PTR_ERR(file);
> -
> - drm_syncobj_get(syncobj);
> - if (cmpxchg(&syncobj->file, NULL, file)) {
> - /* lost the race */
> - fput(file);
> - }
> -
> - return 0;
> -}
> -
> /**
> * drm_syncobj_get_fd - get a file descriptor from a syncobj
> * @syncobj: Sync object to export
> @@ -427,21 +410,24 @@ static int drm_syncobj_alloc_file(struct drm_syncobj *syncobj)
> */
> int drm_syncobj_get_fd(struct drm_syncobj *syncobj, int *p_fd)
> {
> - int ret;
> + struct file *file;
> int fd;
>
> fd = get_unused_fd_flags(O_CLOEXEC);
> if (fd < 0)
> return fd;
>
> - if (!syncobj->file) {
> - ret = drm_syncobj_alloc_file(syncobj);
> - if (ret) {
> - put_unused_fd(fd);
> - return ret;
> - }
> + file = anon_inode_getfile("syncobj_file",
> + &drm_syncobj_file_fops,
> + syncobj, 0);
> + if (IS_ERR(file)) {
> + put_unused_fd(fd);
> + return PTR_ERR(file);
> }
> - fd_install(fd, syncobj->file);
> +
> + drm_syncobj_get(syncobj);
> + fd_install(fd, file);
> +
> *p_fd = fd;
> return 0;
> }
> @@ -461,31 +447,24 @@ static int drm_syncobj_handle_to_fd(struct drm_file *file_private,
> return ret;
> }
>
> -static struct drm_syncobj *drm_syncobj_fdget(int fd)
> -{
> - struct file *file = fget(fd);
> -
> - if (!file)
> - return NULL;
> - if (file->f_op != &drm_syncobj_file_fops)
> - goto err;
> -
> - return file->private_data;
> -err:
> - fput(file);
> - return NULL;
> -};
> -
> static int drm_syncobj_fd_to_handle(struct drm_file *file_private,
> int fd, u32 *handle)
> {
> - struct drm_syncobj *syncobj = drm_syncobj_fdget(fd);
> + struct drm_syncobj *syncobj;
> + struct file *file;
> int ret;
>
> - if (!syncobj)
> + file = fget(fd);
> + if (!file)
> return -EINVAL;
>
> + if (file->f_op != &drm_syncobj_file_fops) {
> + fput(file);
> + return -EINVAL;
> + }
> +
> /* take a reference to put in the idr */
> + syncobj = file->private_data;
> drm_syncobj_get(syncobj);
>
> idr_preload(GFP_KERNEL);
> @@ -494,12 +473,11 @@ static int drm_syncobj_fd_to_handle(struct drm_file *file_private,
> spin_unlock(&file_private->syncobj_table_lock);
> idr_preload_end();
>
> - if (ret < 0) {
> - fput(syncobj->file);
> - return ret;
> - }
> - *handle = ret;
> - return 0;
> + if (ret > 0)
> + *handle = ret;
> +
> + fput(file);
> + return ret;
> }
>
> static int drm_syncobj_import_sync_file_fence(struct drm_file *file_private,
> diff --git a/include/drm/drm_syncobj.h b/include/drm/drm_syncobj.h
> index 3980602472c0..ca5bf7d12d0b 100644
> --- a/include/drm/drm_syncobj.h
> +++ b/include/drm/drm_syncobj.h
> @@ -56,10 +56,6 @@ struct drm_syncobj {
> * @lock: Protects &cb_list and write-locks &fence.
> */
> spinlock_t lock;
> - /**
> - * @file: A file backing for this syncobj.
> - */
> - struct file *file;
> };
>
> typedef void (*drm_syncobj_func_t)(struct drm_syncobj *syncobj,
> --
> 2.15.1
>
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@xxxxxxxxxxxxxxxxxxxxx
> https://lists.freedesktop.org/mailman/listinfo/intel-gfx
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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