[Patch net v3 4/4] tcp: handle pure FIN case correctly

Cong Wang
2022-08-17T19:55:34Z

When skb->len==0, the recv_actor() returns 0 too, but we also use 0
for error conditions. This patch amends this by propagating the errors
to tcp_read_skb() so that we can distinguish skb->len==0 case from
error cases.

Fixes: 04919bed948d ("tcp: Introduce tcp_read_skb()")
Reported-by: Eric Dumazet <edumazet@google.com>
Cc: John Fastabend <john.fastabend@gmail.com>
Cc: Jakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: Cong Wang <cong.wang@bytedance.com>
---
net/core/skmsg.c | 5 +++--
net/ipv4/tcp.c | 2 +-
2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/net/core/skmsg.c b/net/core/skmsg.c
index f47338d89d5d..59e75ffcc1f4 100644
--- a/net/core/skmsg.c
+++ b/net/core/skmsg.c
@@ -1194,8 +1194,9 @@ static int sk_psock_verdict_recv(struct sock *sk, struct sk_buff *skb)
ret = bpf_prog_run_pin_on_cpu(prog, skb);
ret = sk_psock_map_verd(ret, skb_bpf_redirect_fetch(skb));
}
- if (sk_psock_verdict_apply(psock, skb, ret) < 0)
- len = 0;
+ ret = sk_psock_verdict_apply(psock, skb, ret);
+ if (ret < 0)
+ len = ret;
out:
rcu_read_unlock();
return len;
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 56a554b49caa..bbe218753662 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1768,7 +1768,7 @@ int tcp_read_skb(struct sock *sk, skb_read_actor_t recv_actor)
__skb_unlink(skb, &sk->sk_receive_queue);
WARN_ON(!skb_set_owner_sk_safe(skb, sk));
copied = recv_actor(sk, skb);
- if (copied > 0) {
+ if (copied >= 0) {
seq += copied;
if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
++seq;
--
2.34.1