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Message-ID: <CAL4WiipdO5+1Fi_ig5hB25d2LJvc+cjzyAbo8mxx3e4EiRx9YA@mail.gmail.com>
Date: Tue, 31 Jan 2012 03:16:09 +0100
From: Eric Dumazet <eric.dumazet@...il.com>
To: Shawn Lu <shawn.lu@...csson.com>
Cc: davem@...emloft.net, netdev@...r.kernel.org, xiaoclu@...il.com
Subject: Re: [PATCH] tcp: md5: fix md5 RST when both sides have listener
Le 31 janvier 2012 03:07, Shawn Lu <shawn.lu@...csson.com> a écrit :
> TCP RST mechanism is broken in TCP md5(RFC2385). When
> connection is gone, md5 key is lost, sending RST without
> md5 hash is deem to ignored by peer. This can be a problem
> since RST help protocal like bgp fast recove from peer crash.
>
> In most case, users of tcp md5, such as bgp and ldp, have listeners
> on both sides. md5 keys for peers are saved in listening socket.
> When passive side connection is gone, we can still get md5 key
> from listening socket. When active side of connection is gone,
> we can try to find listening socket through source port, and
> then md5 key.
> we are not loosing sercuriy here: packet is valified checked with
> md5 hash. No RST is generated if md5 hash doesn't match or no md5
> key can be found.
>
> Signed-off-by: Shawn Lu <shawn.lu@...csson.com>
> ---
> net/ipv4/tcp_ipv4.c | 31 ++++++++++++++++++++++++++++++-
> net/ipv6/tcp_ipv6.c | 34 ++++++++++++++++++++++++++++++++--
> 2 files changed, 62 insertions(+), 3 deletions(-)
>
> diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
> index 337ba4c..b2358b4 100644
> --- a/net/ipv4/tcp_ipv4.c
> +++ b/net/ipv4/tcp_ipv4.c
> @@ -601,6 +601,9 @@ static void tcp_v4_send_reset(struct sock *sk, struct sk_buff *skb)
> struct ip_reply_arg arg;
> #ifdef CONFIG_TCP_MD5SIG
> struct tcp_md5sig_key *key;
> + __u8 *hash_location = NULL;
> + unsigned char newhash[16];
> + int genhash;
> #endif
> struct net *net;
>
> @@ -631,7 +634,33 @@ static void tcp_v4_send_reset(struct sock *sk, struct sk_buff *skb)
> arg.iov[0].iov_len = sizeof(rep.th);
>
> #ifdef CONFIG_TCP_MD5SIG
> - key = sk ? tcp_v4_md5_do_lookup(sk, ip_hdr(skb)->saddr) : NULL;
> + hash_location = tcp_parse_md5sig_option(th);
> + if (!sk && hash_location) {
> + /*
> + * active side is lost. Try to find listening socket through
> + * source port, and then find md5 key through listening socket.
> + * we are not loose security here:
> + * Incoming packet is checked with md5 hash with finding key,
> + * no RST generated if md5 hash doesn't match.
> + */
> + sk = __inet_lookup_listener(dev_net(skb_dst(skb)->dev),
> + &tcp_hashinfo, ip_hdr(skb)->daddr,
> + ntohs(th->source), inet_iif(skb));
> + /* don't send rst if it can't find key */
> + if (!sk)
> + return;
Now you have a socket in sk, you also are responsible to release the
refcount taken in __inet_lookup_listener()
> + key = tcp_v4_md5_do_lookup(sk, ip_hdr(skb)->saddr);
> + if (!key)
> + return;
leak refcount
> + genhash = tcp_v4_md5_hash_skb(newhash, key,
> + NULL, NULL, skb);
> + if (genhash || memcmp(hash_location, newhash, 16) != 0)
> + return;
same leak
> +
> + } else {
> + key = sk ? tcp_v4_md5_do_lookup(sk, ip_hdr(skb)->saddr) : NULL;
> + }
> +
> if (key) {
> rep.opt[0] = htonl((TCPOPT_NOP << 24) |
> (TCPOPT_NOP << 16) |
> diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
> index 3edd05a..1da99fd 100644
> --- a/net/ipv6/tcp_ipv6.c
> +++ b/net/ipv6/tcp_ipv6.c
> @@ -1074,6 +1074,12 @@ static void tcp_v6_send_reset(struct sock *sk, struct sk_buff *skb)
> const struct tcphdr *th = tcp_hdr(skb);
> u32 seq = 0, ack_seq = 0;
> struct tcp_md5sig_key *key = NULL;
> +#ifdef CONFIG_TCP_MD5SIG
> + __u8 *hash_location = NULL;
> + struct ipv6hdr *ipv6h = ipv6_hdr(skb);
> + unsigned char newhash[16];
> + int genhash;
> +#endif
>
> if (th->rst)
> return;
> @@ -1082,8 +1088,32 @@ static void tcp_v6_send_reset(struct sock *sk, struct sk_buff *skb)
> return;
>
> #ifdef CONFIG_TCP_MD5SIG
> - if (sk)
> - key = tcp_v6_md5_do_lookup(sk, &ipv6_hdr(skb)->saddr);
> + hash_location = tcp_parse_md5sig_option(th);
> + if (!sk && hash_location) {
> + /*
> + * active side is lost. Try to find listening socket through
> + * source port, and then find md5 key through listening socket.
> + * we are not loose security here:
> + * Incoming packet is checked with md5 hash with finding key,
> + * no RST generated if md5 hash doesn't match.
> + */
> + sk = inet6_lookup_listener(dev_net(skb_dst(skb)->dev),
> + &tcp_hashinfo, &ipv6h->daddr,
> + ntohs(th->source), inet6_iif(skb));
> + if (!sk)
> + return;
> +
> + key = tcp_v6_md5_do_lookup(sk, &ipv6h->saddr);
> + if (!key)
> + return;
same leak
> +
> + genhash = tcp_v6_md5_hash_skb(newhash, key,
> + NULL, NULL, skb);
> + if (genhash || memcmp(hash_location, newhash, 16) != 0)
> + return;
same leak
> + } else {
> + key = sk ? tcp_v6_md5_do_lookup(sk, &ipv6h->saddr) : NULL;
> + }
> #endif
>
> if (th->ack)
> --
> 1.7.0.4
>
> --
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