tree 52f996bcb8b01b4d1e4ee3705c0f646e549fa41a
parent 728dba3a39c66b3d8ac889ddbe38b5b1c264aec3
author Eric W. Biederman <ebiederm@xmission.com> 1406590013 -0700
committer Eric W. Biederman <ebiederm@xmission.com> 1406851914 -0700

mnt: Only change user settable mount flags in remount

Kenton Varda <kenton@sandstorm.io> discovered that by remounting a
read-only bind mount read-only in a user namespace the
MNT_LOCK_READONLY bit would be cleared, allowing an unprivileged user
to the remount a read-only mount read-write.

Correct this by replacing the mask of mount flags to preserve
with a mask of mount flags that may be changed, and preserve
all others.   This ensures that any future bugs with this mask and
remount will fail in an easy to detect way where new mount flags
simply won't change.

Cc: stable@vger.kernel.org
Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>