netdev - [PATCH 09/11] netfilter: nat: fix crash when conntrack entry is re-used

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Date:   Wed, 30 Nov 2016 22:57:23 +0100
From:   Pablo Neira Ayuso <pablo@...filter.org>
To:     netfilter-devel@...r.kernel.org
Cc:     davem@...emloft.net, netdev@...r.kernel.org
Subject: [PATCH 09/11] netfilter: nat: fix crash when conntrack entry is re-used

From: Florian Westphal <fw@...len.de>

Stas Nichiporovich reports oops in nf_nat_bysource_cmp(), trying to
access nf_conn struct at address 0xffffffffffffff50.

This is the result of fetching a null rhash list (struct embedded at
offset 176; 0 - 176 gets us ...fff50).

The problem is that conntrack entries are allocated from a
SLAB_DESTROY_BY_RCU cache, i.e. entries can be free'd and reused
on another cpu while nf nat bysource hash access the same conntrack entry.

Freeing is fine (we hold rcu read lock); zeroing rhlist_head isn't.

-> Move the rhlist struct outside of the memset()-inited area.

Fixes: 7c9664351980aaa6a ("netfilter: move nat hlist_head to nf_conn")
Reported-by: Stas Nichiporovich <stasn77@...il.com>
Signed-off-by: Florian Westphal <fw@...len.de>
Signed-off-by: Pablo Neira Ayuso <pablo@...filter.org>
---
 include/net/netfilter/nf_conntrack.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/net/netfilter/nf_conntrack.h b/include/net/netfilter/nf_conntrack.h
index dc143ada9762..d9d52c020a70 100644
--- a/include/net/netfilter/nf_conntrack.h
+++ b/include/net/netfilter/nf_conntrack.h
@@ -100,6 +100,9 @@ struct nf_conn {
 
 	possible_net_t ct_net;
 
+#if IS_ENABLED(CONFIG_NF_NAT)
+	struct rhlist_head nat_bysource;
+#endif
 	/* all members below initialized via memset */
 	u8 __nfct_init_offset[0];
 
@@ -117,9 +120,6 @@ struct nf_conn {
 	/* Extensions */
 	struct nf_ct_ext *ext;
 
-#if IS_ENABLED(CONFIG_NF_NAT)
-	struct rhlist_head nat_bysource;
-#endif
 	/* Storage reserved for other modules, must be the last member */
 	union nf_conntrack_proto proto;
 };
-- 
2.1.4