Re: [musl] libc-test contribution

[Rich Felker <dalias@libc.org>]

On Fri, Aug 16, 2024 at 11:57:29AM -0400, Rich Felker wrote:
> On Fri, Aug 16, 2024 at 09:35:38AM +0200, Szabolcs Nagy wrote:
> > * Ward, Ryan C <ryan.c.ward3@boeing.com> [2024-08-16 01:06:55 +0000]:
> > > Hello,
> > > 
> > > I would like to start contributing some test cases to libc-test. I have 
> > > started with testing some simple recent regressions (e.g. a test for
> > > the recent fix commit 947b4574), and am aiming to start filling in
> > > missing functional test coverage. Am I able to submit the test
> > > directly to this mailing list, and are there any other immediate 
> > > areas of libc-test that need implementation?
> > 
> > this list is fine
> > 
> > there are many areas missing
> > but they need test infrastucture
> > eg networking tests depending on
> > /etc/resolv.conf need to run in
> > a separate mount namespace.
> 
> I could try writing a helper module to do this. Basically it would
> just unshare into a new user+mount+network namespace and, if
> /etc/resolv.conf exists, bind-mount an empty file over it. Then you
> can bind port 53 and it will intercept all queries, and you don't have
> to worry about anything going out to the real network or having
> network-dependent behaviors.

Something like this:

#define _GNU_SOURCE
#include <stdio.h>
#include <unistd.h>
#include <sched.h>
#include <sys/mount.h>
#include <fcntl.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <net/if.h>
#include <netinet/in.h>

int enter_dns_test_ns()
{
	if (unshare(CLONE_NEWUSER|CLONE_NEWNS|CLONE_NEWNET) < 0)
		return -1;
	int s = socket(AF_INET, SOCK_DGRAM, IPPROTO_IP);
	if (s < 0) return -1;
	struct ifreq ifr = {
		.ifr_name = "lo",
		.ifr_addr = (union { struct sockaddr_in sin; struct sockaddr sa; }){{
			.sin_family = AF_INET,
			.sin_port = 0,
			.sin_addr = htonl(0x7f000001),
			}}.sa,
	};
	if (ioctl(s, SIOCSIFADDR, &ifr) < 0)
		return -1;
	if (ioctl(s, SIOCGIFFLAGS, &ifr) < 0)
		return -1;
	ifr.ifr_flags |= IFF_UP;
	if (ioctl(s, SIOCSIFFLAGS, &ifr) < 0)
		return -1;
	char tmp[] = "/tmp/emptyXXXXXX";
	int fd = mkostemp(tmp, O_CLOEXEC);
	if (fd < 0) return -1;
	int r = mount(tmp, "/etc/resolv.conf", 0, MS_BIND, 0);
	unlink(tmp);
	return r;
}