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Consolidate determination of UID/GID to run as

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Currently the logic to work out what UID and GID we will run as is spread
across conf().  If --runas is specified it's handled in conf_runas(),
otherwise it's handled by check_root(), which depends on initialization of
the uid and gid variables by either conf() itself or conf_runas().

Make this clearer by putting all the UID and GID logic into a single
conf_ugid() function.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
This commit is contained in:
David Gibson 2022-09-12 22:24:01 +10:00 committed by Stefano Brivio
parent 10c6347747
commit 80d7012b09
3 changed files with 73 additions and 59 deletions
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81
conf.c
View file

@ -1021,6 +1021,70 @@ static int conf_runas(const char *opt, unsigned int *uid, unsigned int *gid)
#endif /* !GLIBC_NO_STATIC_NSS */
}
/**
* conf_ugid() - Determine UID and GID to run as
* @runas: --runas option, may be NULL
* @uid: User ID, set on success
* @gid: Group ID, set on success
*
* Return: 0 on success, negative error code on failure
*/
static int conf_ugid(const char *runas, uid_t *uid, gid_t *gid)
{
const char root_uid_map[] = " 0 0 4294967295";
struct passwd *pw;
char buf[BUFSIZ];
int ret;
int fd;
/* If user has specified --runas, that takes precedence... */
if (runas) {
ret = conf_runas(runas, uid, gid);
if (ret)
err("Invalid --runas option: %s", runas);
return ret;
}
/* ...otherwise default to current user and group... */
*uid = geteuid();
*gid = getegid();
/* ...as long as it's not root... */
if (*uid)
return 0;
/* ...or at least not root in the init namespace... */
if ((fd = open("/proc/self/uid_map", O_RDONLY | O_CLOEXEC)) < 0)
return 0;
if (read(fd, buf, BUFSIZ) != sizeof(root_uid_map) ||
strncmp(buf, root_uid_map, sizeof(root_uid_map) - 1)) {
close(fd);
return 0;
}
close(fd);
/* ...otherwise use nobody:nobody */
warn("Don't run as root. Changing to nobody...");
#ifndef GLIBC_NO_STATIC_NSS
pw = getpwnam("nobody");
if (!pw) {
perror("getpwnam");
exit(EXIT_FAILURE);
}
*uid = pw->pw_uid;
*gid = pw->pw_gid;
#else
(void)pw;
/* Common value for 'nobody', not really specified */
*uid = *gid = 65534;
#endif
return 0;
}
/**
* conf() - Process command-line arguments and set configuration
* @c: Execution context
@ -1085,9 +1149,10 @@ void conf(struct ctx *c, int argc, char **argv)
struct fqdn *dnss = c->dns_search;
uint32_t *dns4 = c->ip4.dns;
int name, ret, mask, b, i;
const char *runas = NULL;
unsigned int ifi = 0;
uid_t uid = 0;
gid_t gid = 0;
uid_t uid;
gid_t gid;
if (c->mode == MODE_PASTA)
c->no_dhcp_dns = c->no_dhcp_dns_search = 1;
@ -1210,15 +1275,12 @@ void conf(struct ctx *c, int argc, char **argv)
c->trace = c->debug = c->foreground = 1;
break;
case 12:
if (uid || gid) {
if (runas) {
err("Multiple --runas options given");
usage(argv[0]);
}
if (conf_runas(optarg, &uid, &gid)) {
err("Invalid --runas option: %s", optarg);
usage(argv[0]);
}
runas = optarg;
break;
case 'd':
if (c->debug) {
@ -1499,7 +1561,10 @@ void conf(struct ctx *c, int argc, char **argv)
}
} while (name != -1);
check_root(&uid, &gid);
ret = conf_ugid(runas, &uid, &gid);
if (ret)
usage(argv[0]);
drop_root(uid, gid);
if (c->mode == MODE_PASTA) {

50
util.c
View file

@ -482,56 +482,6 @@ void drop_caps(void)
}
}
/**
* check_root() - Check if root in init ns, exit if we can't drop to user
*/
void check_root(uid_t *uid, gid_t *gid)
{
const char root_uid_map[] = " 0 0 4294967295";
struct passwd *pw;
char buf[BUFSIZ];
int fd;
if (!*uid)
*uid = geteuid();
if (!*gid)
*gid = getegid();
if (*uid)
return;
if ((fd = open("/proc/self/uid_map", O_RDONLY | O_CLOEXEC)) < 0)
return;
if (read(fd, buf, BUFSIZ) != sizeof(root_uid_map) ||
strncmp(buf, root_uid_map, sizeof(root_uid_map) - 1)) {
close(fd);
return;
}
close(fd);
if (!*uid) {
fprintf(stderr, "Don't run as root. Changing to nobody...\n");
#ifndef GLIBC_NO_STATIC_NSS
pw = getpwnam("nobody");
if (!pw) {
perror("getpwnam");
exit(EXIT_FAILURE);
}
*uid = pw->pw_uid;
*gid = pw->pw_gid;
#else
(void)pw;
/* Common value for 'nobody', not really specified */
*uid = *gid = 65534;
#endif
}
}
/**
* drop_root() - Switch to given UID and GID
* @uid: User ID to switch to

1
util.h
View file

@ -234,7 +234,6 @@ 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);
void drop_caps(void);
void check_root(uid_t *uid, gid_t *gid);
void drop_root(uid_t uid, gid_t gid);
int ns_enter(const struct ctx *c);
void write_pidfile(int fd, pid_t pid);