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// SPDX-License-Identifier: AGPL-3.0-or-later
/* nsholder - maintain a namespace to be entered by other processes
*
* Copyright Red Hat
* Author: David Gibson <david@gibson.dropbear.id.au>
*
* Can run in 3 modes:
*
* nsholder <path> hold
* Designed to be run inside a namespace, opens a Unix domain
* control socket at <path> and waits until instructed to stop
* with "nsholder <path> stop"
* nsholder <path> pid
* Prints the PID of the nsholder hold process with control
* socket <path>. This is given in the PID namespace where
* nsholder pid is executed, not the one where nsholder hold is
* running
* nsholder <path> stop
* Instruct the nsholder hold with control socket at <path> to exit.
*/
#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <sys/socket.h>
#include <linux/un.h>
#define die(...) \
do { \
fprintf(stderr, __VA_ARGS__); \
exit(1); \
} while (0)
static void usage(void)
{
die("Usage: holder <socket path> hold|pid\n");
}
static void hold(int fd, const struct sockaddr_un *addr)
{
int rc;
rc = bind(fd, (struct sockaddr *)addr, sizeof(*addr));
if (rc < 0)
die("bind(): %s\n", strerror(errno));
rc = listen(fd, 0);
if (rc < 0)
die("listen(): %s\n", strerror(errno));
printf("nsholder: local PID=%d local UID=%u local GID=%u\n",
getpid(), getuid(), getgid());
do {
int afd = accept(fd, NULL, NULL);
char buf;
if (afd < 0)
die("accept(): %s\n", strerror(errno));
rc = read(afd, &buf, sizeof(buf));
if (rc < 0)
die("read(): %s\n", strerror(errno));
} while (rc == 0);
unlink(addr->sun_path);
}
static void pid(int fd, const struct sockaddr_un *addr)
{
int rc;
struct ucred peercred;
socklen_t optlen = sizeof(peercred);
do {
rc = connect(fd, (struct sockaddr *)addr, sizeof(*addr));
if (rc < 0 && errno != ENOENT && errno != ECONNREFUSED)
die("connect(): %s\n", strerror(errno));
} while (rc < 0);
rc = getsockopt(fd, SOL_SOCKET, SO_PEERCRED,
&peercred, &optlen);
if (rc < 0)
die("getsockopet(SO_PEERCRED): %s\n", strerror(errno));
close(fd);
printf("%d\n", peercred.pid);
}
static void stop(int fd, const struct sockaddr_un *addr)
{
int rc;
char buf = 'Q';
rc = connect(fd, (struct sockaddr *)addr, sizeof(*addr));
if (rc < 0)
die("connect(): %s\n", strerror(errno));
rc = write(fd, &buf, sizeof(buf));
if (rc < 0)
die("write(): %s\n", strerror(errno));
close(fd);
}
int main(int argc, char *argv[])
{
int fd;
const char *sockname;
struct sockaddr_un sockaddr = {
.sun_family = AF_UNIX,
};
if (argc != 3)
usage();
sockname = argv[1];
strncpy(sockaddr.sun_path, sockname, UNIX_PATH_MAX);
fd = socket(AF_UNIX, SOCK_STREAM, PF_UNIX);
if (fd < 0)
die("socket(): %s\n", strerror(errno));
if (strcmp(argv[2], "hold") == 0)
hold(fd, &sockaddr);
else if (strcmp(argv[2], "pid") == 0)
pid(fd, &sockaddr);
else if (strcmp(argv[2], "stop") == 0)
stop(fd, &sockaddr);
else
usage();
exit(0);
}
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