network: ignore -EINVAL from bpf_get_current_comm()

Hopefully fixes #40051.

src/network/bpf/sysctl-monitor/sysctl-monitor.bpf.c

@@ -2,6 +2,7 @@
 
 #include "vmlinux.h"
 
+#include <errno.h>
 #include <bpf/bpf_helpers.h>
 
 #include "sysctl-write-event.h"
@@ -104,7 +105,7 @@ int sysctl_monitor(struct bpf_sysctl *ctx) {
                 return 1;
 
         r = bpf_get_current_comm(we.comm, sizeof(we.comm));
-        if (r < 0) {
+        if (r < 0 && r != -EINVAL) { /* -EINVAL: the process is already vanished */
                 we.errorcode = r;
                 goto send_event;
         }

src/network/networkd-sysctl.c

@@ -76,13 +76,13 @@ static int sysctl_event_handler(void *ctx, void *data, size_t data_sz) {
                 log_struct(LOG_WARNING,
                            LOG_MESSAGE_ID(SD_MESSAGE_SYSCTL_CHANGED_STR),
                            LOG_ITEM("OBJECT_PID=" PID_FMT, we->pid),
-                           LOG_ITEM("OBJECT_COMM=%s", we->comm),
+                           LOG_ITEM("OBJECT_COMM=%s", empty_to_na(we->comm)),
                            LOG_ITEM("SYSCTL=%s", path),
                            LOG_ITEM("OLDVALUE=%s", we->current),
                            LOG_ITEM("NEWVALUE=%s", we->newvalue),
                            LOG_ITEM("OURVALUE=%s", value),
                            LOG_MESSAGE("Foreign process '%s[" PID_FMT "]' changed sysctl '%s' from '%s' to '%s', conflicting with our setting to '%s'.",
-                                       we->comm, we->pid, path, we->current, we->newvalue, value));
+                                       empty_to_na(we->comm), we->pid, path, we->current, we->newvalue, value));
 
         return 0;
 }