From: Eric W. Biederman <ebiederm@xmission.com>
Date: Tue, 29 Jul 2014 00:10:56 +0000 (-0700)
Subject: mnt: Move the test for MNT_LOCK_READONLY from change_mount_flags into do_remount
X-Git-Tag: TizenStudio_2.0_p2.3.1~46
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=8997549011bd9489aa85efabc17439af3a3e730f;p=sdk%2Femulator%2Femulator-kernel.git

mnt: Move the test for MNT_LOCK_READONLY from change_mount_flags into do_remount

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.

Change-Id: I14503e2b7b4f7330f8b8bfa7c26938bafb6c54b5
Cc: stable@vger.kernel.org
Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---

diff --git a/fs/namespace.c b/fs/namespace.c
index 130dff8fda3e..0b958c396391 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1806,9 +1806,6 @@ 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
@@ -1834,6 +1831,16 @@ 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;