Enable the setfl() helper to handle idmapped mounts by passing down the
mount's user namespace. If the initial user namespace is passed nothing
changes so non-idmapped mounts will see identical behavior as before.

Link: https://lore.kernel.org/r/20210112220124.837960-27-christian.brauner@ubuntu.com (local)
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Howells <dhowells@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner <redacted>
---
/* v2 */
patch introduced

/* v3 */
unchanged

/* v4 */
unchanged

/* v5 */
unchanged
base-commit: 7c53f6b671f4aba70ff15e1b05148b10d58c2837

/* v6 */
base-commit: 19c329f6808995b142b3966301f217c831e7cf31

- Christoph Hellwig [off-list ref]:
  - Use file_mnt_user_ns() helper.
---
 fs/fcntl.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/fcntl.c b/fs/fcntl.c
index 74d99731fd43..f6ac5285060d 100644
--- a/fs/fcntl.c
+++ b/fs/fcntl.c

@@ -25,6 +25,7 @@
 #include <linux/user_namespace.h>
 #include <linux/memfd.h>
 #include <linux/compat.h>
+#include <linux/mount.h>
 
 #include <linux/poll.h>
 #include <asm/siginfo.h>

@@ -46,7 +47,7 @@ static int setfl(int fd, struct file * filp, unsigned long arg)
 
 	/* O_NOATIME can only be set by the owner or superuser */
 	if ((arg & O_NOATIME) && !(filp->f_flags & O_NOATIME))
-		if (!inode_owner_or_capable(&init_user_ns, inode))
+		if (!inode_owner_or_capable(file_mnt_user_ns(filp), inode))
 			return -EPERM;
 
 	/* required for strict SunOS emulation */

-- 
2.30.0