[PATCH net 3/4] netfilter: cttimeout: fix slab-out-of-bounds read in cttimeout_net_exit

[Pablo Neira Ayuso <pablo@netfilter.org>]

From: Florian Westphal <fw@strlen.de>

syzbot reports:
BUG: KASAN: slab-out-of-bounds in __list_del_entry_valid+0xcc/0xf0 lib/list_debug.c:42
[..]
 list_del include/linux/list.h:148 [inline]
 cttimeout_net_exit+0x211/0x540 net/netfilter/nfnetlink_cttimeout.c:617

No reproducer so far. Looking at recent changes in this area
its clear that the free_head must not be at the end of the
structure because nf_ct_timeout structure has variable size.

Reported-by: <syzbot+92968395eedbdbd3617d@syzkaller.appspotmail.com>
Fixes: 78222bacfca9 ("netfilter: cttimeout: decouple unlink and free on netns destruction")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
---
 net/netfilter/nfnetlink_cttimeout.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/net/netfilter/nfnetlink_cttimeout.c b/net/netfilter/nfnetlink_cttimeout.c
index f069c24c6146..af15102bc696 100644
--- a/net/netfilter/nfnetlink_cttimeout.c
+++ b/net/netfilter/nfnetlink_cttimeout.c
@@ -35,12 +35,13 @@ static unsigned int nfct_timeout_id __read_mostly;
 
 struct ctnl_timeout {
 	struct list_head	head;
+	struct list_head	free_head;
 	struct rcu_head		rcu_head;
 	refcount_t		refcnt;
 	char			name[CTNL_TIMEOUT_NAME_MAX];
-	struct nf_ct_timeout	timeout;
 
-	struct list_head	free_head;
+	/* must be at the end */
+	struct nf_ct_timeout	timeout;
 };
 
 struct nfct_timeout_pernet {
-- 
2.30.2