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mnt: Move the test for MNT_LOCK_READONLY from change_mount_flags into do_remount

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commit 07b645589dcda8b7a5249e096fece2a67556f0f4 upstream.

There are no races as locked mount flags are guaranteed to never change.

Moving the test into do_remount makes it more visible, and ensures all
filesystem remounts pass the MNT_LOCK_READONLY permission check.  This
second case is not an issue today as filesystem remounts are guarded
by capable(CAP_DAC_ADMIN) and thus will always fail in less privileged
mount namespaces, but it could become an issue in the future.

Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Eric W. Biederman 2014-07-28 17:10:56 -07:00 committed by Greg Kroah-Hartman
parent 8c30f22757
commit 81d4c13ebb
1 changed files with 10 additions and 3 deletions
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13
fs/namespace.c
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@ -1764,9 +1764,6 @@ static int change_mount_flags(struct vfsmount *mnt, int ms_flags)
if (readonly_request == __mnt_is_readonly(mnt))
return 0;
if (mnt->mnt_flags & MNT_LOCK_READONLY)
return -EPERM;
if (readonly_request)
error = mnt_make_readonly(real_mount(mnt));
else
@ -1792,6 +1789,16 @@ static int do_remount(struct path *path, int flags, int mnt_flags,
if (path->dentry != path->mnt->mnt_root)
return -EINVAL;
/* Don't allow changing of locked mnt flags.
*
* No locks need to be held here while testing the various
* MNT_LOCK flags because those flags can never be cleared
* once they are set.
*/
if ((mnt->mnt.mnt_flags & MNT_LOCK_READONLY) &&
!(mnt_flags & MNT_READONLY)) {
return -EPERM;
}
err = security_sb_remount(sb, data);
if (err)
return err;