Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace

Pull userns fix from Eric Biederman:
 "This contains just a single small patch that fixes a tiny hole in the
  logic of allowing unprivileged mounting of proc and sysfs.

  In practice I don't think anyone is affected because having MNT_RDONLY
  clear in mnt->mnt_flags but MS_RDONLY set in sb->s_flags is very weird
  for a filesystem, and weirder for proc and sysfs.  However if it
  happens let's handle it correctly and then no one has to to worry
  about this crazy case"

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace:
  mnt: Account for MS_RDONLY in fs_fully_visible

1 files changed, 4 insertions, 0 deletions

diff --git a/fs/namespace.c b/fs/namespace.c
index a7ec92c051f5..783004af5707 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -3247,6 +3247,10 @@ static bool fs_fully_visible(struct file_system_type *type, int *new_mnt_flags)
                 if (mnt->mnt.mnt_sb->s_iflags & SB_I_NOEXEC)
                         mnt_flags &= ~(MNT_LOCK_NOSUID | MNT_LOCK_NOEXEC);
 
+                /* Don't miss readonly hidden in the superblock flags */
+                if (mnt->mnt.mnt_sb->s_flags & MS_RDONLY)
+                        mnt_flags |= MNT_LOCK_READONLY;
+
                 /* Verify the mount flags are equal to or more permissive
                  * than the proposed new mount.
                  */