| From | Greg Kroah-Hartman <> | Subject | [PATCH 3.10 41/71] mnt: Move the test for MNT_LOCK_READONLY from change_mount_flags into do_remount | Date | Mon, 15 Sep 2014 12:26:39 -0700 |
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3.10-stable review patch. If anyone has any objections, please let me know.
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From: "Eric W. Biederman" <ebiederm@xmission.com>
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>
--- fs/namespace.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-)
--- a/fs/namespace.c +++ b/fs/namespace.c @@ -1764,9 +1764,6 @@ static int change_mount_flags(struct vfs 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, 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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