From: Eric Dumazet Date: Sat, 8 Apr 2017 15:07:33 +0000 (-0700) Subject: tcp: clear saved_syn in tcp_disconnect() X-Git-Tag: v4.9.26~37 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=479beb4c6554bab1f944a5cfb9672a0f9c6892b2;p=thirdparty%2Fkernel%2Fstable.git tcp: clear saved_syn in tcp_disconnect() [ Upstream commit 17c3060b1701fc69daedb4c90be6325d3d9fca8e ] In the (very unlikely) case a passive socket becomes a listener, we do not want to duplicate its saved SYN headers. This would lead to double frees, use after free, and please hackers and various fuzzers Tested: 0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3 +0 setsockopt(3, IPPROTO_TCP, TCP_SAVE_SYN, [1], 4) = 0 +0 fcntl(3, F_SETFL, O_RDWR|O_NONBLOCK) = 0 +0 bind(3, ..., ...) = 0 +0 listen(3, 5) = 0 +0 < S 0:0(0) win 32972 +0 > S. 0:0(0) ack 1 <...> +.1 < . 1:1(0) ack 1 win 257 +0 accept(3, ..., ...) = 4 +0 connect(4, AF_UNSPEC, ...) = 0 +0 close(3) = 0 +0 bind(4, ..., ...) = 0 +0 listen(4, 5) = 0 +0 < S 0:0(0) win 32972 +0 > S. 0:0(0) ack 1 <...> +.1 < . 1:1(0) ack 1 win 257 Fixes: cd8ae85299d5 ("tcp: provide SYN headers for passive connections") Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index 6a90a0e130dca..eb142ca71fc53 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -2297,6 +2297,7 @@ int tcp_disconnect(struct sock *sk, int flags) tcp_init_send_head(sk); memset(&tp->rx_opt, 0, sizeof(tp->rx_opt)); __sk_dst_reset(sk); + tcp_saved_syn_free(tp); WARN_ON(inet->inet_num && !icsk->icsk_bind_hash);