bpf: do not blindly change rlimit in reuseport net selftest

If the current process has unlimited RLIMIT_MEMLOCK,
we should should leave it as is.

Fixes: 941ff6f1 ("bpf: fix rlimit in reuseport net selftest")
Signed-off-by: John Sperbeck <jsperbeck@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

tools/testing/selftests/net/reuseport_bpf.c

@@ -437,14 +437,19 @@ void enable_fastopen(void)
 	}
 }
 
-static struct rlimit rlim_old, rlim_new;
+static struct rlimit rlim_old;
 
 static  __attribute__((constructor)) void main_ctor(void)
 {
 	getrlimit(RLIMIT_MEMLOCK, &rlim_old);
-	rlim_new.rlim_cur = rlim_old.rlim_cur + (1UL << 20);
-	rlim_new.rlim_max = rlim_old.rlim_max + (1UL << 20);
-	setrlimit(RLIMIT_MEMLOCK, &rlim_new);
+
+	if (rlim_old.rlim_cur != RLIM_INFINITY) {
+		struct rlimit rlim_new;
+
+		rlim_new.rlim_cur = rlim_old.rlim_cur + (1UL << 20);
+		rlim_new.rlim_max = rlim_old.rlim_max + (1UL << 20);
+		setrlimit(RLIMIT_MEMLOCK, &rlim_new);
+	}
 }
 
 static __attribute__((destructor)) void main_dtor(void)