Re: [PATCH bpf v2 02/15] bpf, sockmap: Don't let an SK_DROP verdict stick

[Jiayuan Chen <jiayuan.chen@linux.dev>]

On 11/2/26 3:20 PM, Alexei Starovoitov wrote:
> From: Josef Bacik <josef@toxicpanda.com>
>
> The verdict of an sk_msg prog is valid for one message, or for the bytes
> that bpf_msg_apply_bytes() requests. These bytes can come from many
> sendmsg() calls. Thus tcp_bpf_send_verdict() keeps the verdict in
> psock->eval and runs the prog only when psock->eval is __SK_NONE. The code
> that resets psock->eval is after the switch statement, but the __SK_DROP
> branch returns before that code. Then sendmsg() drops all subsequent
> messages with -EACCES and does not run the prog.
>
> Reset psock->eval when apply_bytes is 0, as the __SK_REDIRECT branch does.
>
> Fixes: 4f738adba30a ("bpf: create tcp_bpf_ulp allowing BPF to monitor socket TX/RX data")
> Signed-off-by: Josef Bacik <josef@toxicpanda.com>
> Signed-off-by: Alexei Starovoitov <ast@kernel.org>


Reviewed-by: Jiayuan Chen <jiayuan.chen@linux.dev>


> ---
>  net/ipv4/tcp_bpf.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/net/ipv4/tcp_bpf.c b/net/ipv4/tcp_bpf.c
> index 8cf63a9e7fed..d90bcc911b36 100644
> --- a/net/ipv4/tcp_bpf.c
> +++ b/net/ipv4/tcp_bpf.c
> @@ -509,6 +509,9 @@ static int tcp_bpf_send_verdict(struct sock *sk, struct sk_psock *psock,
>  	default:
>  		sk_msg_free(sk, msg);
>  		sk_msg_apply_bytes(psock, tosend);
> +		/* The verdict holds for apply_bytes, not for ever */
> +		if (!psock->apply_bytes)
> +			psock->eval = __SK_NONE;
>  		*copied -= (tosend + delta);
>  		return -EACCES;
>  	}