linux-kernel - [PATCH 3.2 43/46] nf_conntrack: avoid kernel pointer value leak in slab name

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Message-ID: <lsq.1465767282.695667051@decadent.org.uk>
Date:	Sun, 12 Jun 2016 22:34:42 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "David S. Miller" <davem@...emloft.net>,
	"Eric Dumazet" <eric.dumazet@...il.com>,
	"Linus Torvalds" <torvalds@...ux-foundation.org>
Subject: [PATCH 3.2 43/46] nf_conntrack: avoid kernel pointer value leak
 in slab name

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

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

From: Linus Torvalds <torvalds@...ux-foundation.org>

commit 31b0b385f69d8d5491a4bca288e25e63f1d945d0 upstream.

The slab name ends up being visible in the directory structure under
/sys, and even if you don't have access rights to the file you can see
the filenames.

Just use a 64-bit counter instead of the pointer to the 'net' structure
to generate a unique name.

This code will go away in 4.7 when the conntrack code moves to a single
kmemcache, but this is the backportable simple solution to avoiding
leaking kernel pointers to user space.

Fixes: 5b3501faa874 ("netfilter: nf_conntrack: per netns nf_conntrack_cachep")
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Acked-by: Eric Dumazet <eric.dumazet@...il.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 net/netfilter/nf_conntrack_core.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/net/netfilter/nf_conntrack_core.c
+++ b/net/netfilter/nf_conntrack_core.c
@@ -1493,6 +1493,7 @@ err_proto:
 
 static int nf_conntrack_init_net(struct net *net)
 {
+	static atomic64_t unique_id;
 	int ret;
 
 	atomic_set(&net->ct.count, 0);
@@ -1504,7 +1505,8 @@ static int nf_conntrack_init_net(struct
 		goto err_stat;
 	}
 
-	net->ct.slabname = kasprintf(GFP_KERNEL, "nf_conntrack_%p", net);
+	net->ct.slabname = kasprintf(GFP_KERNEL, "nf_conntrack_%llu",
+				(u64)atomic64_inc_return(&unique_id));
 	if (!net->ct.slabname) {
 		ret = -ENOMEM;
 		goto err_slabname;