random-util: include pidfdid in fallback RNG buffer

This doesn't make the RNG cryptographic strength, but if we have it
easily accessible, why not include the pidfd id. It is after all not
vulnerable to reuse.

src/basic/random-util.c

@@ -23,6 +23,7 @@
 #include "missing_syscall.h"
 #include "missing_threads.h"
 #include "parse-util.h"
+#include "pidfd-util.h"
 #include "process-util.h"
 #include "random-util.h"
 #include "sha256.h"
@@ -39,6 +40,7 @@ static void fallback_random_bytes(void *p, size_t n) {
                 uint64_t call_id, block_id;
                 usec_t stamp_mono, stamp_real;
                 pid_t pid, tid;
+                uint64_t pidfdid;
                 uint8_t auxval[16];
         } state = {
                 /* Arbitrary domain separation to prevent other usage of AT_RANDOM from clashing. */
@@ -51,6 +53,7 @@ static void fallback_random_bytes(void *p, size_t n) {
 
         memcpy(state.label, "systemd fallback random bytes v1", sizeof(state.label));
         memcpy(state.auxval, ULONG_TO_PTR(getauxval(AT_RANDOM)), sizeof(state.auxval));
+        (void) pidfd_get_inode_id_self_cached(&state.pidfdid);
 
         while (n > 0) {
                 struct sha256_ctx ctx;