On Wed, Jan 22, 2025 at 06:09 PM +08, Jiayuan Chen wrote:
'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.
Fixes: e5c6de5fa025 ("bpf, sockmap: Incorrectly handling copied_seq") Suggested-by: Jakub Sitnicki jakub@cloudflare.com Signed-off-by: Jiayuan Chen mrpre@163.com
I'm happy with how this turned out, but let's run it by Eric.
Reviewed-by: Jakub Sitnicki jakub@cloudflare.com