fix buf wrong tcp checksum conputation

ubuntu_intermediate/inter_op_ebpf.c

@@ -29,30 +29,35 @@ static inline __u16 csum_fold_helper(__u32 csum)
     return ~csum;
 }
 
-static __always_inline __u32 sum16(const void *data, __u32 size, const void *data_end)
-{
+static __always_inline __u32 sum16(const void* data, __u32 size, const void* data_end) {
     __u32 s = 0;
+    __u16 *buf = (__u16 *)data;
     for (__u32 i = 0; i < MAX_CSUM_WORDS; i++)
     {
         if (2 * i >= size)
         {
+            // bpf_trace_printk("csum4: %lx", s);
             return s; /* normal exit */
         }
-        if (data + 2 * i + 1 + 1 > data_end)
+        if ((void *)(buf + 1) > data_end)
         {
-            return 0; /* should be unreachable */
+            // bpf_trace_printk("csum5: %lx", s);
+            return 0;
         }
-        s += ((const __u16 *)data)[i];
+        s += *buf++;
 
-        if (2 * i + 1 == size)
+        if (2 * i + 3 == size)
         {
-            __u8 byte;
-            if (bpf_probe_read_kernel(&byte, sizeof(byte), data + (i * 2 + 1)))
-                return 0;
+            if (data + 2 * i + 3 > data_end)
+            {
+                return 0; /* should be unreachable */
+            }
+            __u8 byte = *((__u8 *)data + 2*i + 2);
             s += byte;
+            // bpf_trace_printk("csum3: %lx, bytes: %x, byte2: %x", s, byte);
+            return s;
         }
     }
-
     return s;
 }
 
@@ -67,18 +72,18 @@ static inline __u16 tcp_checksum(struct iphdr *ip, struct tcphdr *tcp, void *dat
         return 0;
 
     // 2. Pseudo-header
-    csum += (ip->saddr >> 16) & 0xFFFF;
-    csum += ip->saddr & 0xFFFF;
-    csum += (ip->daddr >> 16) & 0xFFFF;
-    csum += ip->daddr & 0xFFFF;
+    csum += (ip->saddr >> 16) + (ip->saddr & 0xFFFF); 
+    csum += (ip->daddr >> 16) + (ip->daddr & 0xFFFF);
     csum += htons(6);
     csum += htons(tcp_len);
+    bpf_trace_printk("csum1: %lx", csum);
 
     // 3. Manual unrolling (safer than loops)
     __u16 *ptr = (__u16 *)tcp;
     __u16 words = tcp_len / 2;
 
     csum += sum16(tcp, tcp_len, data_end);
+    bpf_trace_printk("csum2: %lx", csum);
 
     return csum_fold_helper(csum);
 }