ignore egress packets on sockets used for RX

code/bngblaster/src/io/io_socket.c

@@ -132,6 +132,22 @@ io_socket_open(io_handle_s *io) {
             io->interface->name, strerror(errno), errno);
         return false;
     }
+    /* Ignore outgoing packets if socket is used for RX. 
+     * PACKET_IGNORE_OUTGOING option is supported since linux 4.20. */
+    if(io->direction == IO_INGRESS) {
+        int one=1;
+        if(setsockopt(io->fd, SOL_PACKET, PACKET_IGNORE_OUTGOING, &one, sizeof(one)) == -1) {
+            kernel_version_s kv = get_kernel_version();
+            const char *hint = "";
+            if((kv.major < 4) || (kv.major == 4 && kv.minor < 20)) {
+                hint = " Unsupported on linux kernel below 4.20.";
+            }
+            LOG(ERROR,
+                "Warning: Failed to set PACKET_IGNORE_OUTGOING for interface %s RX socket - %s (%d).%s"
+                " TX packets might be seen on RX.\n",
+                io->interface->name, strerror(errno), errno, hint);
+        }
+    }
     if(io->direction == IO_EGRESS && interface->config->qdisc_bypass) {
         if(!set_qdisc_bypass(io)) {
             return false;

code/common/src/utils.c

@@ -8,6 +8,27 @@
  * SPDX-License-Identifier: BSD-3-Clause
  */
 #include "utils.h"
+#include <sys/utsname.h>
+
+/*
+ * Get linux kernel version major,minor and patch number.
+ */
+kernel_version_s get_kernel_version(void)
+{
+    struct utsname buffer;
+    kernel_version_s kv = {0, 0, 0};
+
+    if (uname(&buffer) != 0) {
+        return kv;  // returns zeros on failure
+    }
+
+    sscanf(buffer.release, "%u.%u.%u",
+           &kv.major,
+           &kv.minor,
+           &kv.patch);
+
+    return kv;
+}
 
 /*
  * Simple big endian reader.

code/common/src/utils.h

@@ -11,6 +11,15 @@
 #define __COMMON_UTILS_H__
 #include "common.h"
 
+typedef struct kernel_version_
+{
+    uint32_t major;
+    uint32_t minor;
+    uint32_t patch;
+} kernel_version_s;
+
+kernel_version_s get_kernel_version(void);
+
 uint64_t read_be_uint(uint8_t *data, size_t length);
 bool write_be_uint(uint8_t *data, size_t length, uint64_t value);
 bool inc_be_uint(uint8_t *data, size_t length);