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tcp: Clear sk_send_head after purging the write queue

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Denis Andzakovic discovered a potential use-after-free in older kernel
versions, using syzkaller.  tcp_write_queue_purge() frees all skbs in
the TCP write queue and can leave sk->sk_send_head pointing to freed
memory.  tcp_disconnect() clears that pointer after calling
tcp_write_queue_purge(), but tcp_connect() does not.  It is
(surprisingly) possible to add to the write queue between
disconnection and reconnection, so this needs to be done in both
places.

This bug was introduced by backports of commit 7f582b248d0a ("tcp:
purge write queue in tcp_connect_init()") and does not exist upstream
because of earlier changes in commit 75c119afe14f ("tcp: implement
rb-tree based retransmit queue").  The latter is a major change that's
not suitable for stable.

Reported-by: Denis Andzakovic <denis.andzakovic@pulsesecurity.co.nz>
Bisected-by: Salvatore Bonaccorso <carnil@debian.org>
Fixes: 7f582b248d0a ("tcp: purge write queue in tcp_connect_init()")
Cc: <stable@vger.kernel.org> # before 4.15
Cc: Eric Dumazet <edumazet@google.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
CVE-2020-0040
Signed-off-by: Kevin F. Haggerty <haggertk@lineageos.org>
Change-Id: I3c20d87056584d59741e8c94137c495e37581d84
This commit is contained in:
Ben Hutchings
2020-05-20 09:44:16 +02:00
committed by Francescodario Cuzzocrea
parent c5d010c7ba
commit acfd0496f7
1 changed files with 3 additions and 0 deletions
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include/net/tcp.h
+3
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@@ -1256,6 +1256,8 @@ extern int tcp_md5_hash_skb_data(struct tcp_md5sig_pool *, const struct sk_buff
extern int tcp_md5_hash_key(struct tcp_md5sig_pool *hp,
const struct tcp_md5sig_key *key);
static inline void tcp_init_send_head(struct sock *sk);
/* write queue abstraction */
static inline void tcp_write_queue_purge(struct sock *sk)
{
@@ -1263,6 +1265,7 @@ static inline void tcp_write_queue_purge(struct sock *sk)
while ((skb = __skb_dequeue(&sk->sk_write_queue)) != NULL)
sk_wmem_free_skb(sk, skb);
tcp_init_send_head(sk);
sk_mem_reclaim(sk);
tcp_clear_all_retrans_hints(tcp_sk(sk));
}