netdev - [PATCH net] tcp: cleanup copied_seq and urg_data in tcp

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Message-Id: <20180708060001.59291-1-edumazet@google.com>
Date:   Sat,  7 Jul 2018 23:00:01 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     "David S . Miller" <davem@...emloft.net>
Cc:     netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>
Subject: [PATCH net] tcp: cleanup copied_seq and urg_data in tcp_disconnect

tcp_zerocopy_receive() relies on tcp_inq() to limit number of bytes
requested by user.

syzbot found that after tcp_disconnect(), tcp_inq() was returning
a stale value (number of bytes in queue before the disconnect).

Note that after this patch, ioctl(fd, SIOCINQ, &val) is also fixed
and returns 0, so this might be a candidate for all known linux kernels.

While we are at this, we probably also should clear urg_data to
avoid other syzkaller reports after it discovers how to deal with
urgent data.

syzkaller repro :

socket(PF_INET, SOCK_STREAM, IPPROTO_IP) = 3
bind(3, {sa_family=AF_INET, sin_port=htons(20000), sin_addr=inet_addr("224.0.0.1")}, 16) = 0
connect(3, {sa_family=AF_INET, sin_port=htons(20000), sin_addr=inet_addr("127.0.0.1")}, 16) = 0
send(3, ..., 4096, 0) = 4096
connect(3, {sa_family=AF_UNSPEC, sa_data="\0\0\0\0\0\0\0\0\0\0\0\0\0\0"}, 128) = 0
getsockopt(3, SOL_TCP, TCP_ZEROCOPY_RECEIVE, ..., [16]) = 0 // CRASH

Fixes: 05255b823a61 ("tcp: add TCP_ZEROCOPY_RECEIVE support for zerocopy receive")
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Reported-by: syzbot <syzkaller@...glegroups.com>
---
 net/ipv4/tcp.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index c959bb6ea4ed7c7e236a701209ec3aa493961a0a..0d43705dd001c4bf6d41afd5515327c7585da184 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2562,6 +2562,8 @@ int tcp_disconnect(struct sock *sk, int flags)
 
 	tcp_clear_xmit_timers(sk);
 	__skb_queue_purge(&sk->sk_receive_queue);
+	tp->copied_seq = tp->rcv_nxt;
+	tp->urg_data = 0;
 	tcp_write_queue_purge(sk);
 	tcp_fastopen_active_disable_ofo_check(sk);
 	skb_rbtree_purge(&tp->out_of_order_queue);
-- 
2.18.0.203.gfac676dfb9-goog