fs/fuse: fix ioctl type confusion

fuse_dev_ioctl() performed fuse_get_dev() on a user-supplied fd,
leading to a type confusion issue. Fix it by checking file->f_op.

Signed-off-by: Jann Horn <jann@thejh.net>
Acked-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 9 insertions, 1 deletions

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 80cc1b35d460..ebb5e37455a0 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -2246,7 +2246,15 @@ static long fuse_dev_ioctl(struct file *file, unsigned int cmd,
 
                         err = -EINVAL;
                         if (old) {
-                                struct fuse_dev *fud = fuse_get_dev(old);
+                                struct fuse_dev *fud = NULL;
+
+                                /*
+                                 * Check against file->f_op because CUSE
+                                 * uses the same ioctl handler.
+                                 */
+                                if (old->f_op == file->f_op &&
+                                    old->f_cred->user_ns == file->f_cred->user_ns)
+                                        fud = fuse_get_dev(old);
 
                                 if (fud) {
                                         mutex_lock(&fuse_mutex);