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Commit 07b64558 authored by Eric W. Biederman's avatar Eric W. Biederman
Browse files

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.

Cc: stable@vger.kernel.org
Acked-by: default avatarSerge E. Hallyn <serge.hallyn@ubuntu.com>
Signed-off-by: default avatar"Eric W. Biederman" <ebiederm@xmission.com>
parent a6138db8

fs/namespace.c

+10 −3
Original line number Diff line number Diff line
@@ -1896,9 +1896,6 @@ 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
@@ -1924,6 +1921,16 @@ 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;