netdev - [PATCH bpf v2 3/4] bpf, sockmap: Fix data loss caused by using apply

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Message-Id: <1669634685-1717-4-git-send-email-yangpc@wangsu.com>
Date:   Mon, 28 Nov 2022 19:24:44 +0800
From:   Pengcheng Yang <yangpc@...gsu.com>
To:     bpf@...r.kernel.org, netdev@...r.kernel.org,
        John Fastabend <john.fastabend@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jakub Sitnicki <jakub@...udflare.com>,
        Lorenz Bauer <lmb@...udflare.com>
Cc:     Pengcheng Yang <yangpc@...gsu.com>
Subject: [PATCH bpf v2 3/4] bpf, sockmap: Fix data loss caused by using apply_bytes on ingress redirect

Use apply_bytes on ingress redirect, when apply_bytes is less than
the length of msg data, some data may be skipped and lost in
bpf_tcp_ingress().
If there is still data in the scatterlist that has not been consumed,
we cannot move the msg iter.

Fixes: 604326b41a6f ("bpf, sockmap: convert to generic sk_msg interface")
Signed-off-by: Pengcheng Yang <yangpc@...gsu.com>
---
 net/ipv4/tcp_bpf.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/ipv4/tcp_bpf.c b/net/ipv4/tcp_bpf.c
index ac883c9..722a8c0 100644
--- a/net/ipv4/tcp_bpf.c
+++ b/net/ipv4/tcp_bpf.c
@@ -45,8 +45,11 @@ static int bpf_tcp_ingress(struct sock *sk, struct sk_psock *psock,
 		tmp->sg.end = i;
 		if (apply) {
 			apply_bytes -= size;
-			if (!apply_bytes)
+			if (!apply_bytes) {
+				if (sge->length)
+					sk_msg_iter_var_prev(i);
 				break;
+			}
 		}
 	} while (i != msg->sg.end);
 
-- 
1.8.3.1