linux-kernel - [PATCH 3.16 178/366] Don't leak MNT_INTERNAL away from internal mounts

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Message-ID: <lsq.1539530741.941417219@decadent.org.uk>
Date:   Sun, 14 Oct 2018 16:25:41 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Al Viro" <viro@...iv.linux.org.uk>,
        "Kirill Tkhai" <ktkhai@...tuozzo.com>,
        "Alexander Aring" <aring@...atatu.com>
Subject: [PATCH 3.16 178/366] Don't leak MNT_INTERNAL away from internal
 mounts

3.16.60-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Al Viro <viro@...iv.linux.org.uk>

commit 16a34adb9392b2fe4195267475ab5b472e55292c upstream.

We want it only for the stuff created by SB_KERNMOUNT mounts, *not* for
their copies.  As it is, creating a deep stack of bindings of /proc/*/ns/*
somewhere in a new namespace and exiting yields a stack overflow.

Reported-by: Alexander Aring <aring@...atatu.com>
Bisected-by: Kirill Tkhai <ktkhai@...tuozzo.com>
Tested-by: Kirill Tkhai <ktkhai@...tuozzo.com>
Tested-by: Alexander Aring <aring@...atatu.com>
Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 fs/namespace.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -903,7 +903,8 @@ static struct mount *clone_mnt(struct mo
 			goto out_free;
 	}
 
-	mnt->mnt.mnt_flags = old->mnt.mnt_flags & ~(MNT_WRITE_HOLD|MNT_MARKED);
+	mnt->mnt.mnt_flags = old->mnt.mnt_flags;
+	mnt->mnt.mnt_flags &= ~(MNT_WRITE_HOLD|MNT_MARKED|MNT_INTERNAL);
 	/* Don't allow unprivileged users to change mount flags */
 	if (flag & CL_UNPRIVILEGED) {
 		mnt->mnt.mnt_flags |= MNT_LOCK_ATIME;