xdp-synproxy: allow enable disable wscale option

this is to workaround XDP synproxy intermittent small packet transmission issue when window scale, time stamp is enabled see #7 ./xdp_synproxy --iface lo --mss4 1460 --mss6 1440 --wscale 0 --ttl 64 --ports 443 result XDP generated SYNACK TCP Options: (4 bytes), Maximum segment size ./xdp_synproxy --iface lo --mss4 1460 --mss6 1440 --wscale 7 --ttl 64 --ports 443 result XDP generated SYNACK TCP Options: (16 bytes), Maximum segment size, SACK permitted, Timestamps, NOP, Wscale Signed-off-by: Vincent Li <[email protected]>
vincentmli · Nov 11, 2024 · 72cd8df · 72cd8df
1 parent 2a7e3ef
commit 72cd8df
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Showing 2 changed files with 18 additions and 9 deletions.
diff --git a/xdp-synproxy/xdp_synproxy.bpf.c b/xdp-synproxy/xdp_synproxy.bpf.c
@@ -56,7 +56,7 @@
 
 #define DEFAULT_MSS4 1460
 #define DEFAULT_MSS6 1440
-#define DEFAULT_WSCALE 7
+#define DEFAULT_WSCALE 0
 #define DEFAULT_TTL 64
 #define MAX_ALLOWED_PORTS 8
 
@@ -488,6 +488,9 @@ static __always_inline __u8 tcp_mkoptions(__be32 *buf, __be32 *tsopt, __u16 mss,
 	if (!tsopt)
 		return buf - start;
 
+	if ( wscale == 0 )
+		return buf - start;
+
 	if (tsopt[0] & bpf_htonl(1 << 4))
 		*buf++ = bpf_htonl((TCPOPT_SACK_PERM << 24) |
 				   (TCPOLEN_SACK_PERM << 16) |

diff --git a/xdp-synproxy/xdp_synproxy.c b/xdp-synproxy/xdp_synproxy.c
@@ -84,8 +84,8 @@ static void parse_options(int argc, char *argv[], unsigned int *ifindex, __u32 *
 		{ "ports", required_argument, NULL, 'p' },
 		{ NULL, 0, NULL, 0 },
 	};
-	unsigned long mss4, wscale, ttl;
-	unsigned long long mss6;
+
+	unsigned long mss4 = 0, mss6 = 0, wscale = 0, ttl = 0;
 	unsigned int tcpipopts_mask = 0;
 
 	if (argc < 2)
@@ -143,12 +143,18 @@ static void parse_options(int argc, char *argv[], unsigned int *ifindex, __u32 *
 	if (optind < argc)
 		help(argv[0]);
 
-	if (tcpipopts_mask == 0xf) {
-		if (mss4 == 0 || mss6 == 0 || wscale == 0 || ttl == 0)
-			help(argv[0]);
-		*tcpipopts = (mss6 << 32) | (ttl << 24) | (wscale << 16) | mss4;
-	} else if (tcpipopts_mask != 0) {
-		help(argv[0]);
+	// Construct tcpipopts based on provided options
+	if (tcpipopts_mask & (1 << 0)) {  // mss4 provided
+		*tcpipopts |= mss4;
+	}
+	if (tcpipopts_mask & (1 << 1)) {  // mss6 provided
+		*tcpipopts |= ((unsigned long long)mss6 << 32);
+	}
+	if (tcpipopts_mask & (1 << 2)) {  // wscale provided
+		*tcpipopts |= ((unsigned long long)wscale << 16);
+	}
+	if (tcpipopts_mask & (1 << 3)) {  // ttl provided
+		*tcpipopts |= ((unsigned long long)ttl << 24);
 	}
 
 	if (*ifindex != 0 && *prog_id != 0)