From: Eric W. Biederman 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: upstream/snapshot3+hdmi~1708 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=9810174c0384f725a31be1dfc64a881695ad465d;p=platform%2Fadaptation%2Frenesas_rcar%2Frenesas_kernel.git mnt: Move the test for MNT_LOCK_READONLY from change_mount_flags into do_remount 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 Signed-off-by: "Eric W. Biederman" Signed-off-by: Greg Kroah-Hartman --- diff --git a/fs/namespace.c b/fs/namespace.c index b613b5f..2b8649b 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -1887,9 +1887,6 @@ 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 @@ -1915,6 +1912,16 @@ 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;