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util, conf: Add and use ns_is_init() helper

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We'll need this in isolate_initial(). While at it, don't rely on
BUFSIZ: the earlier issue we had with musl reminded me it's not a
magic "everything will fit" value. Size the read buffer to what we
actually need from uid_map, and check for the final newline too,
because uid_map is organised in lines.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
This commit is contained in:
Stefano Brivio 2023-05-21 14:47:07 +02:00
parent 25f1d1a84f
commit b0881aae6d
3 changed files with 28 additions and 15 deletions
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16
conf.c
View file

@ -1096,10 +1096,6 @@ static int conf_runas(char *opt, unsigned int *uid, unsigned int *gid)
*/
static void conf_ugid(char *runas, uid_t *uid, gid_t *gid)
{
const char root_uid_map[] = " 0 0 4294967295";
char buf[BUFSIZ];
int fd;
/* If user has specified --runas, that takes precedence... */
if (runas) {
if (conf_runas(runas, uid, gid))
@ -1116,18 +1112,8 @@ static void conf_ugid(char *runas, uid_t *uid, gid_t *gid)
return;
/* ...or at least not root in the init namespace... */
if ((fd = open("/proc/self/uid_map", O_RDONLY | O_CLOEXEC)) < 0) {
die("Can't determine if we're in init namespace: %s",
strerror(errno));
}
if (read(fd, buf, BUFSIZ) != sizeof(root_uid_map) ||
strncmp(buf, root_uid_map, sizeof(root_uid_map) - 1)) {
close(fd);
if (!ns_is_init())
return;
}
close(fd);
/* ...otherwise use nobody:nobody */
warn("Don't run as root. Changing to nobody...");

25
util.c
View file

@ -390,6 +390,31 @@ int ns_enter(const struct ctx *c)
return 0;
}
/**
* ns_is_init() - Is the caller running in the "init" user namespace?
*
* Return: true if caller is in init, false otherwise, won't return on failure
*/
bool ns_is_init(void)
{
const char root_uid_map[] = " 0 0 4294967295\n";
char buf[sizeof(root_uid_map)] = { 0 };
bool ret = true;
int fd;
if ((fd = open("/proc/self/uid_map", O_RDONLY | O_CLOEXEC)) < 0) {
die("Can't determine if we're in init namespace: %s",
strerror(errno));
}
if (read(fd, buf, sizeof(root_uid_map)) != sizeof(root_uid_map) - 1 ||
strncmp(buf, root_uid_map, sizeof(root_uid_map)))
ret = false;
close(fd);
return ret;
}
/**
* pid_file() - Write PID to file, if requested to do so, and close it
* @fd: Open PID file descriptor, closed on exit, -1 to skip writing it

2
util.h
View file

@ -8,6 +8,7 @@
#include <stdlib.h>
#include <stdarg.h>
#include <stdbool.h>
#include "log.h"
@ -216,6 +217,7 @@ char *line_read(char *buf, size_t len, int fd);
void procfs_scan_listen(struct ctx *c, uint8_t proto, int ip_version, int ns,
uint8_t *map, uint8_t *exclude);
int ns_enter(const struct ctx *c);
bool ns_is_init(void);
void write_pidfile(int fd, pid_t pid);
int __daemon(int pidfile_fd, int devnull_fd);
int fls(unsigned long x);