From: Eric Dumazet <eduma...@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 <eduma...@google.com>
Reported-by: Marco Grassi <marco....@gmail.com>
Reported-by: Vladis Dronov <vdro...@redhat.com>
---
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;
