From: Petar Penkov <ppenkov@google.com>
Date: Tue, 27 Aug 2019 23:46:22 +0000 (-0700)
Subject: bpf: fix error check in bpf_tcp_gen_syncookie
X-Git-Url: http://git.lede-project.org./?a=commitdiff_plain;h=0741be358d5adc266244f909e4434fe17fe1a109;p=openwrt%2Fstaging%2Fblogic.git

bpf: fix error check in bpf_tcp_gen_syncookie

If a SYN cookie is not issued by tcp_v#_gen_syncookie, then the return
value will be exactly 0, rather than <= 0. Let's change the check to
reflect that, especially since mss is an unsigned value and cannot be
negative.

Fixes: 70d66244317e ("bpf: add bpf_tcp_gen_syncookie helper")
Reported-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Petar Penkov <ppenkov@google.com>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
---

diff --git a/net/core/filter.c b/net/core/filter.c
index 0c1059cdad3d..17bc9af8f156 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -5903,7 +5903,7 @@ BPF_CALL_5(bpf_tcp_gen_syncookie, struct sock *, sk, void *, iph, u32, iph_len,
 	default:
 		return -EPROTONOSUPPORT;
 	}
-	if (mss <= 0)
+	if (mss == 0)
 		return -ENOENT;
 
 	return cookie | ((u64)mss << 32);