[PATCH 5.4 172/658] bpf, sockmap: Fix data loss caused by using apply_bytes on ingress redirect

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From: Pengcheng Yang <yangpc@xxxxxxxxxx>

[ Upstream commit 9072931f020bfd907d6d89ee21ff1481cd78b407 ]

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@xxxxxxxxxx>
Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Acked-by: Jakub Sitnicki <jakub@xxxxxxxxxxxxxx>
Link: https://lore.kernel.org/bpf/1669718441-2654-4-git-send-email-yangpc@xxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 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 229fa1f2b381..ca49d68a0e04 100644
--- a/net/ipv4/tcp_bpf.c
+++ b/net/ipv4/tcp_bpf.c
@@ -203,8 +203,11 @@ 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);
 
-- 
2.35.1






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