fuse: always allow query of st_dev

Fuse mounts without "allow_other" are off-limits to all non-owners.  Yet it
makes sense to allow querying st_dev on the root, since this value is
provided by the kernel, not the userspace filesystem.

Allow statx(2) with a zero request mask to succeed on a fuse mounts for all
users.

Reported-by: Nikolaus Rath <Nikolaus@rath.org>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index de1e2fd..26f028b 100644 (file)
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -1689,8 +1689,18 @@ static int fuse_getattr(const struct path *path, struct kstat *stat,
        struct inode *inode = d_inode(path->dentry);
        struct fuse_conn *fc = get_fuse_conn(inode);
 
-       if (!fuse_allow_current_process(fc))
+       if (!fuse_allow_current_process(fc)) {
+               if (!request_mask) {
+                       /*
+                        * If user explicitly requested *nothing* then don't
+                        * error out, but return st_dev only.
+                        */
+                       stat->result_mask = 0;
+                       stat->dev = inode->i_sb->s_dev;
+                       return 0;
+               }
                return -EACCES;
+       }
 
        return fuse_update_get_attr(inode, NULL, stat, request_mask, flags);
 }