linux-kernel - [PATCH 4.16 189/196] Dont leak MNT_INTERNAL away from internal mounts

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Date:   Sun, 22 Apr 2018 15:53:29 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, stable@...nel.org,
        Alexander Aring <aring@...atatu.com>,
        Kirill Tkhai <ktkhai@...tuozzo.com>,
        Al Viro <viro@...iv.linux.org.uk>
Subject: [PATCH 4.16 189/196] Dont leak MNT_INTERNAL away from internal mounts

4.16-stable 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.

Cc: stable@...nel.org
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: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/namespace.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1089,7 +1089,8 @@ 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;