[PATCH bpf v9 2/5] bpf: fix wrong copied_seq calculation

Jiayuan Chen
2025-01-22T10:11:47Z

'sk->copied_seq' was updated in the tcp_eat_skb() function when the action
of a BPF program was SK_REDIRECT. For other actions, like SK_PASS, the
update logic for 'sk->copied_seq' was moved to tcp_bpf_recvmsg_parser()
to ensure the accuracy of the 'fionread' feature.

It works for a single stream_verdict scenario, as it also modified
sk_data_ready->sk_psock_verdict_data_ready->tcp_read_skb
to remove updating 'sk->copied_seq'.

However, for programs where both stream_parser and stream_verdict are
active (strparser purpose), tcp_read_sock() was used instead of
tcp_read_skb() (sk_data_ready->strp_data_ready->tcp_read_sock).
tcp_read_sock() now still updates 'sk->copied_seq', leading to duplicate
updates.

In summary, for strparser + SK_PASS, copied_seq is redundantly calculated
in both tcp_read_sock() and tcp_bpf_recvmsg_parser().

The issue causes incorrect copied_seq calculations, which prevent
correct data reads from the recv() interface in user-land.

We do not want to add new proto_ops to implement a new version of
tcp_read_sock, as this would introduce code complexity [1].

We could have added noack and copied_seq to desc, and then called
ops->read_sock. However, unfortunately, other modules didn’t fully
initialize desc to zero. So, for now, we are directly calling
tcp_read_sock_noack() in tcp_bpf.c.

[1]: https://lore.kernel.org/bpf/20241218053408.437295-1-mrpre@163.com
Fixes: e5c6de5fa025 ("bpf, sockmap: Incorrectly handling copied_seq")
Suggested-by: Jakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: Jiayuan Chen <mrpre@163.com>
---
include/linux/skmsg.h | 2 ++
include/net/tcp.h | 8 ++++++++
net/core/skmsg.c | 7 +++++++
net/ipv4/tcp.c | 29 ++++++++++++++++++++++++-----
net/ipv4/tcp_bpf.c | 36 ++++++++++++++++++++++++++++++++++++
5 files changed, 77 insertions(+), 5 deletions(-)

diff --git a/include/linux/skmsg.h b/include/linux/skmsg.h
index 2cbe0c22a32f..0b9095a281b8 100644
--- a/include/linux/skmsg.h
+++ b/include/linux/skmsg.h
@@ -91,6 +91,8 @@ struct sk_psock {
struct sk_psock_progs progs;
#if IS_ENABLED(CONFIG_BPF_STREAM_PARSER)
struct strparser strp;
+ u32 copied_seq;
+ u32 ingress_bytes;
#endif
struct sk_buff_head ingress_skb;
struct list_head ingress_msg;
diff --git a/include/net/tcp.h b/include/net/tcp.h
index e9b37b76e894..06affc653247 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -729,6 +729,9 @@ void tcp_get_info(struct sock *, struct tcp_info *);
/* Read 'sendfile()'-style from a TCP socket */
int tcp_read_sock(struct sock *sk, read_descriptor_t *desc,
sk_read_actor_t recv_actor);
+int tcp_read_sock_noack(struct sock *sk, read_descriptor_t *desc,
+ sk_read_actor_t recv_actor, bool noack,
+ u32 *copied_seq);
int tcp_read_skb(struct sock *sk, skb_read_actor_t recv_actor);
struct sk_buff *tcp_recv_skb(struct sock *sk, u32 seq, u32 *off);
void tcp_read_done(struct sock *sk, size_t len);
@@ -2599,6 +2602,11 @@ struct sk_psock;
#ifdef CONFIG_BPF_SYSCALL
int tcp_bpf_update_proto(struct sock *sk, struct sk_psock *psock, bool restore);
void tcp_bpf_clone(const struct sock *sk, struct sock *newsk);
+#ifdef CONFIG_BPF_STREAM_PARSER
+struct strparser;
+int tcp_bpf_strp_read_sock(struct strparser *strp, read_descriptor_t *desc,
+ sk_read_actor_t recv_actor);
+#endif /* CONFIG_BPF_STREAM_PARSER */
#endif /* CONFIG_BPF_SYSCALL */

#ifdef CONFIG_INET
diff --git a/net/core/skmsg.c b/net/core/skmsg.c
index 61f3f3d4e528..0ddc4c718833 100644
--- a/net/core/skmsg.c
+++ b/net/core/skmsg.c
@@ -549,6 +549,9 @@ static int sk_psock_skb_ingress_enqueue(struct sk_buff *skb,
return num_sge;
}

+#if IS_ENABLED(CONFIG_BPF_STREAM_PARSER)
+ psock->ingress_bytes += len;
+#endif
copied = len;
msg->sg.start = 0;
msg->sg.size = copied;
@@ -1144,6 +1147,10 @@ int sk_psock_init_strp(struct sock *sk, struct sk_psock *psock)
if (!ret)
sk_psock_set_state(psock, SK_PSOCK_RX_STRP_ENABLED);

+ if (sk_is_tcp(sk)) {
+ psock->strp.cb.read_sock = tcp_bpf_strp_read_sock;
+ psock->copied_seq = tcp_sk(sk)->copied_seq;
+ }
return ret;
}

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 0d704bda6c41..285678d8ce07 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1565,12 +1565,13 @@ EXPORT_SYMBOL(tcp_recv_skb);
* or for 'peeking' the socket using this routine
* (although both would be easy to implement).
*/
-int tcp_read_sock(struct sock *sk, read_descriptor_t *desc,
- sk_read_actor_t recv_actor)
+static int __tcp_read_sock(struct sock *sk, read_descriptor_t *desc,
+ sk_read_actor_t recv_actor, bool noack,
+ u32 *copied_seq)
{
struct sk_buff *skb;
struct tcp_sock *tp = tcp_sk(sk);
- u32 seq = tp->copied_seq;
+ u32 seq = *copied_seq;
u32 offset;
int copied = 0;

@@ -1624,9 +1625,12 @@ int tcp_read_sock(struct sock *sk, read_descriptor_t *desc,
tcp_eat_recv_skb(sk, skb);
if (!desc->count)
break;
- WRITE_ONCE(tp->copied_seq, seq);
+ WRITE_ONCE(*copied_seq, seq);
}
- WRITE_ONCE(tp->copied_seq, seq);
+ WRITE_ONCE(*copied_seq, seq);
+
+ if (noack)
+ goto out;

tcp_rcv_space_adjust(sk);

@@ -1635,10 +1639,25 @@ int tcp_read_sock(struct sock *sk, read_descriptor_t *desc,
tcp_recv_skb(sk, seq, &offset);
tcp_cleanup_rbuf(sk, copied);
}
+out:
return copied;
}
+
+int tcp_read_sock(struct sock *sk, read_descriptor_t *desc,
+ sk_read_actor_t recv_actor)
+{
+ return __tcp_read_sock(sk, desc, recv_actor, false,
+ &tcp_sk(sk)->copied_seq);
+}
EXPORT_SYMBOL(tcp_read_sock);

+int tcp_read_sock_noack(struct sock *sk, read_descriptor_t *desc,
+ sk_read_actor_t recv_actor, bool noack,
+ u32 *copied_seq)
+{
+ return __tcp_read_sock(sk, desc, recv_actor, noack, copied_seq);
+}
+
int tcp_read_skb(struct sock *sk, skb_read_actor_t recv_actor)
{
struct sk_buff *skb;
diff --git a/net/ipv4/tcp_bpf.c b/net/ipv4/tcp_bpf.c
index 47f65b1b70ca..ba581785adb4 100644
--- a/net/ipv4/tcp_bpf.c
+++ b/net/ipv4/tcp_bpf.c
@@ -646,6 +646,42 @@ static int tcp_bpf_assert_proto_ops(struct proto *ops)
ops->sendmsg == tcp_sendmsg ? 0 : -ENOTSUPP;
}

+#if IS_ENABLED(CONFIG_BPF_STREAM_PARSER)
+int tcp_bpf_strp_read_sock(struct strparser *strp, read_descriptor_t *desc,
+ sk_read_actor_t recv_actor)
+{
+ struct sock *sk = strp->sk;
+ struct sk_psock *psock;
+ struct tcp_sock *tp;
+ int copied = 0;
+
+ tp = tcp_sk(sk);
+ rcu_read_lock();
+ psock = sk_psock(sk);
+ if (WARN_ON_ONCE(!psock)) {
+ desc->error = -EINVAL;
+ goto out;
+ }
+
+ psock->ingress_bytes = 0;
+ copied = tcp_read_sock_noack(sk, desc, recv_actor, true,
+ &psock->copied_seq);
+ if (copied < 0)
+ goto out;
+ /* recv_actor may redirect skb to another socket (SK_REDIRECT) or
+ * just put skb into ingress queue of current socket (SK_PASS).
+ * For SK_REDIRECT, we need to ack the frame immediately but for
+ * SK_PASS, we want to delay the ack until tcp_bpf_recvmsg_parser().
+ */
+ tp->copied_seq = psock->copied_seq - psock->ingress_bytes;
+ tcp_rcv_space_adjust(sk);
+ __tcp_cleanup_rbuf(sk, copied - psock->ingress_bytes);
+out:
+ rcu_read_unlock();
+ return copied;
+}
+#endif /* CONFIG_BPF_STREAM_PARSER */
+
int tcp_bpf_update_proto(struct sock *sk, struct sk_psock *psock, bool restore)
{
int family = sk->sk_family == AF_INET6 ? TCP_BPF_IPV6 : TCP_BPF_IPV4;
--
2.43.5