mnt: Move the test for MNT_LOCK_READONLY from change_mount_flags into do_remount (07b64558) · Commits · 戴 / test

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:

Serge E. Hallyn <serge.hallyn@ubuntu.com> Signed-off-by:

"Eric W. Biederman" <ebiederm@xmission.com>

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;

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