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Date: Mon, 15 Sep 2014 12:25:49 -0700 From: Greg Kroah-Hartman <gregkh@...uxfoundation.org> To: linux-kernel@...r.kernel.org Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, stable@...r.kernel.org, "Serge E. Hallyn" <serge.hallyn@...ntu.com>, "Eric W. Biederman" <ebiederm@...ssion.com> Subject: [PATCH 3.16 110/158] mnt: Move the test for MNT_LOCK_READONLY from change_mount_flags into do_remount 3.16-stable review patch. If anyone has any objections, please let me know. ------------------ From: "Eric W. Biederman" <ebiederm@...ssion.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@...ntu.com> Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org> --- fs/namespace.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) --- a/fs/namespace.c +++ b/fs/namespace.c @@ -1896,9 +1896,6 @@ 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 @@ -1924,6 +1921,16 @@ 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; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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