[PATCH net] tcp: take care of truncations done by sk_filter()
From: Eric Dumazet <hidden>
Date: 2016-11-10 20:50:21
Subsystem:
networking [general], networking [tcp], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Neal Cardwell, Linus Torvalds
From: Eric Dumazet <edumazet@google.com> With syzkaller help, Marco Grassi found a bug in TCP stack, crashing in tcp_collapse() Root cause is that sk_filter() can truncate the incoming skb, but TCP stack was not really expecting this to happen. It probably was expecting a simple DROP or ACCEPT behavior. We first need to make sure no part of TCP header could be removed. Then we need to adjust TCP_SKB_CB(skb)->end_seq Many thanks to syzkaller team and Marco for giving us a reproducer. Signed-off-by: Eric Dumazet <edumazet@google.com> Reported-by: Marco Grassi <redacted> Reported-by: Vladis Dronov <redacted> --- include/net/tcp.h | 1 + net/ipv4/tcp_ipv4.c | 17 ++++++++++++++++- net/ipv6/tcp_ipv6.c | 5 +++-- 3 files changed, 20 insertions(+), 3 deletions(-)
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 304a8e17bc87..b572f722dbdc 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h@@ -1220,6 +1220,7 @@ static inline void tcp_prequeue_init(struct tcp_sock *tp) bool tcp_prequeue(struct sock *sk, struct sk_buff *skb); bool tcp_add_backlog(struct sock *sk, struct sk_buff *skb); +struct tcphdr *tcp_filter(struct sock *sk, struct sk_buff *skb); #undef STATE_TRACE
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 61b7be303eec..cad14d1bc5a5 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c@@ -1564,6 +1564,20 @@ bool tcp_add_backlog(struct sock *sk, struct sk_buff *skb) } EXPORT_SYMBOL(tcp_add_backlog); +struct tcphdr *tcp_filter(struct sock *sk, struct sk_buff *skb) +{ + struct tcphdr *th = (struct tcphdr *)skb->data; + unsigned int eaten = skb->len; + + if (sk_filter_trim_cap(sk, skb, th->doff * 4)) + return NULL; + eaten -= skb->len; + TCP_SKB_CB(skb)->end_seq -= eaten; + + return (struct tcphdr *)skb->data; +} +EXPORT_SYMBOL(tcp_filter); + /* * From tcp_input.c */
@@ -1676,7 +1690,8 @@ int tcp_v4_rcv(struct sk_buff *skb) nf_reset(skb); - if (sk_filter(sk, skb)) + th = tcp_filter(sk, skb); + if (!th) goto discard_and_relse; skb->dev = NULL;
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 6ca23c2e76f7..208552750550 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c@@ -1229,7 +1229,7 @@ static int tcp_v6_do_rcv(struct sock *sk, struct sk_buff *skb) if (skb->protocol == htons(ETH_P_IP)) return tcp_v4_do_rcv(sk, skb); - if (sk_filter(sk, skb)) + if (!tcp_filter(sk, skb)) goto discard; /*
@@ -1457,7 +1457,8 @@ static int tcp_v6_rcv(struct sk_buff *skb) if (tcp_v6_inbound_md5_hash(sk, skb)) goto discard_and_relse; - if (sk_filter(sk, skb)) + th = tcp_filter(sk, skb); + if (!th) goto discard_and_relse; skb->dev = NULL;