selftests/bpf: fix file descriptor assertion in open_tuntap helper

The open_tuntap helper function uses open() to get a file descriptor for
/dev/net/tun.

The open(2) manpage writes this about its return value:

  On success, open(), openat(), and creat() return the new file
  descriptor (a nonnegative integer).  On error, -1 is returned and
  errno is set to indicate the error.

This means that the fd > 0 assertion in the open_tuntap helper is
incorrect and should rather check for fd >= 0.

When running the BPF selftests locally, this incorrect assertion was not
an issue, but the BPF kernel-patches CI failed because of this:

  open_tuntap:FAIL:open(/dev/net/tun) unexpected open(/dev/net/tun):
  actual 0 <= expected 0

Signed-off-by: Marcus Wichelmann <[email protected]>

Author: MarcusWichelmann

tools/testing/selftests/bpf/network_helpers.c

@@ -571,7 +571,7 @@ int open_tuntap(const char *dev_name, bool need_mac)
 	struct ifreq ifr;
 	int fd = open("/dev/net/tun", O_RDWR);
 
-	if (!ASSERT_GT(fd, 0, "open(/dev/net/tun)"))
+	if (!ASSERT_GE(fd, 0, "open(/dev/net/tun)"))
 		return -1;
 
 	ifr.ifr_flags = IFF_NO_PI | (need_mac ? IFF_TAP : IFF_TUN);