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Systemd/src/basic/user-util.c

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/* SPDX-License-Identifier: LGPL-2.1+ */
/***
This file is part of systemd.
Copyright 2010 Lennart Poettering
***/
#include <alloca.h>
#include <errno.h>
#include <fcntl.h>
#include <grp.h>
#include <pwd.h>
#include <stddef.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <unistd.h>
#include <utmp.h>
#include "alloc-util.h"
#include "fd-util.h"
#include "fileio.h"
#include "format-util.h"
#include "macro.h"
#include "missing.h"
#include "parse-util.h"
#include "path-util.h"
#include "string-util.h"
#include "strv.h"
#include "user-util.h"
#include "utf8.h"
bool uid_is_valid(uid_t uid) {
/* Also see POSIX IEEE Std 1003.1-2008, 2016 Edition, 3.436. */
/* Some libc APIs use UID_INVALID as special placeholder */
if (uid == (uid_t) UINT32_C(0xFFFFFFFF))
return false;
/* A long time ago UIDs where 16bit, hence explicitly avoid the 16bit -1 too */
if (uid == (uid_t) UINT32_C(0xFFFF))
return false;
return true;
}
int parse_uid(const char *s, uid_t *ret) {
uint32_t uid = 0;
int r;
assert(s);
assert_cc(sizeof(uid_t) == sizeof(uint32_t));
r = safe_atou32(s, &uid);
if (r < 0)
return r;
if (!uid_is_valid(uid))
return -ENXIO; /* we return ENXIO instead of EINVAL
* here, to make it easy to distuingish
* invalid numeric uids from invalid
* strings. */
if (ret)
*ret = uid;
return 0;
}
char* getlogname_malloc(void) {
uid_t uid;
struct stat st;
if (isatty(STDIN_FILENO) && fstat(STDIN_FILENO, &st) >= 0)
uid = st.st_uid;
else
uid = getuid();
return uid_to_name(uid);
}
char *getusername_malloc(void) {
const char *e;
e = getenv("USER");
if (e)
return strdup(e);
return uid_to_name(getuid());
}
int get_user_creds(
const char **username,
uid_t *uid, gid_t *gid,
const char **home,
const char **shell) {
struct passwd *p;
uid_t u;
assert(username);
assert(*username);
/* We enforce some special rules for uid=0 and uid=65534: in order to avoid NSS lookups for root we hardcode
* their user record data. */
if (STR_IN_SET(*username, "root", "0")) {
*username = "root";
if (uid)
*uid = 0;
if (gid)
*gid = 0;
if (home)
*home = "/root";
if (shell)
*shell = "/bin/sh";
return 0;
}
if (synthesize_nobody() &&
STR_IN_SET(*username, NOBODY_USER_NAME, "65534")) {
*username = NOBODY_USER_NAME;
if (uid)
*uid = UID_NOBODY;
if (gid)
*gid = GID_NOBODY;
if (home)
*home = "/";
if (shell)
*shell = "/sbin/nologin";
return 0;
}
if (parse_uid(*username, &u) >= 0) {
errno = 0;
p = getpwuid(u);
/* If there are multiple users with the same id, make
* sure to leave $USER to the configured value instead
* of the first occurrence in the database. However if
* the uid was configured by a numeric uid, then let's
* pick the real username from /etc/passwd. */
if (p)
*username = p->pw_name;
} else {
errno = 0;
p = getpwnam(*username);
}
if (!p)
return errno > 0 ? -errno : -ESRCH;
if (uid) {
if (!uid_is_valid(p->pw_uid))
return -EBADMSG;
*uid = p->pw_uid;
}
if (gid) {
if (!gid_is_valid(p->pw_gid))
return -EBADMSG;
*gid = p->pw_gid;
}
if (home)
*home = p->pw_dir;
if (shell)
*shell = p->pw_shell;
return 0;
}
static inline bool is_nologin_shell(const char *shell) {
return PATH_IN_SET(shell,
/* 'nologin' is the friendliest way to disable logins for a user account. It prints a nice
* message and exits. Different distributions place the binary at different places though,
* hence let's list them all. */
"/bin/nologin",
"/sbin/nologin",
"/usr/bin/nologin",
"/usr/sbin/nologin",
/* 'true' and 'false' work too for the same purpose, but are less friendly as they don't do
* any message printing. Different distributions place the binary at various places but at
* least not in the 'sbin' directory. */
"/bin/false",
"/usr/bin/false",
"/bin/true",
"/usr/bin/true");
}
int get_user_creds_clean(
const char **username,
uid_t *uid, gid_t *gid,
const char **home,
const char **shell) {
int r;
/* Like get_user_creds(), but resets home/shell to NULL if they don't contain anything relevant. */
r = get_user_creds(username, uid, gid, home, shell);
if (r < 0)
return r;
if (shell &&
(isempty(*shell) || is_nologin_shell(*shell)))
*shell = NULL;
if (home && empty_or_root(*home))
*home = NULL;
return 0;
}
int get_group_creds(const char **groupname, gid_t *gid) {
struct group *g;
gid_t id;
assert(groupname);
/* We enforce some special rules for gid=0: in order to avoid
* NSS lookups for root we hardcode its data. */
if (STR_IN_SET(*groupname, "root", "0")) {
*groupname = "root";
if (gid)
*gid = 0;
return 0;
}
if (synthesize_nobody() &&
STR_IN_SET(*groupname, NOBODY_GROUP_NAME, "65534")) {
*groupname = NOBODY_GROUP_NAME;
if (gid)
*gid = GID_NOBODY;
return 0;
}
if (parse_gid(*groupname, &id) >= 0) {
errno = 0;
g = getgrgid(id);
if (g)
*groupname = g->gr_name;
} else {
errno = 0;
g = getgrnam(*groupname);
}
if (!g)
return errno > 0 ? -errno : -ESRCH;
if (gid) {
if (!gid_is_valid(g->gr_gid))
return -EBADMSG;
*gid = g->gr_gid;
}
return 0;
}
char* uid_to_name(uid_t uid) {
char *ret;
int r;
/* Shortcut things to avoid NSS lookups */
if (uid == 0)
return strdup("root");
if (synthesize_nobody() &&
uid == UID_NOBODY)
return strdup(NOBODY_USER_NAME);
if (uid_is_valid(uid)) {
long bufsize;
bufsize = sysconf(_SC_GETPW_R_SIZE_MAX);
if (bufsize <= 0)
bufsize = 4096;
for (;;) {
struct passwd pwbuf, *pw = NULL;
_cleanup_free_ char *buf = NULL;
buf = malloc(bufsize);
if (!buf)
return NULL;
r = getpwuid_r(uid, &pwbuf, buf, (size_t) bufsize, &pw);
if (r == 0 && pw)
return strdup(pw->pw_name);
if (r != ERANGE)
break;
bufsize *= 2;
}
}
if (asprintf(&ret, UID_FMT, uid) < 0)
return NULL;
return ret;
}
char* gid_to_name(gid_t gid) {
char *ret;
int r;
if (gid == 0)
return strdup("root");
if (synthesize_nobody() &&
gid == GID_NOBODY)
return strdup(NOBODY_GROUP_NAME);
if (gid_is_valid(gid)) {
long bufsize;
bufsize = sysconf(_SC_GETGR_R_SIZE_MAX);
if (bufsize <= 0)
bufsize = 4096;
for (;;) {
struct group grbuf, *gr = NULL;
_cleanup_free_ char *buf = NULL;
buf = malloc(bufsize);
if (!buf)
return NULL;
r = getgrgid_r(gid, &grbuf, buf, (size_t) bufsize, &gr);
if (r == 0 && gr)
return strdup(gr->gr_name);
if (r != ERANGE)
break;
bufsize *= 2;
}
}
if (asprintf(&ret, GID_FMT, gid) < 0)
return NULL;
return ret;
}
int in_gid(gid_t gid) {
long ngroups_max;
gid_t *gids;
int r, i;
if (getgid() == gid)
return 1;
if (getegid() == gid)
return 1;
if (!gid_is_valid(gid))
return -EINVAL;
ngroups_max = sysconf(_SC_NGROUPS_MAX);
assert(ngroups_max > 0);
gids = newa(gid_t, ngroups_max);
r = getgroups(ngroups_max, gids);
if (r < 0)
return -errno;
for (i = 0; i < r; i++)
if (gids[i] == gid)
return 1;
return 0;
}
int in_group(const char *name) {
int r;
gid_t gid;
r = get_group_creds(&name, &gid);
if (r < 0)
return r;
return in_gid(gid);
}
int get_home_dir(char **_h) {
struct passwd *p;
const char *e;
char *h;
uid_t u;
assert(_h);
/* Take the user specified one */
e = secure_getenv("HOME");
if (e && path_is_absolute(e)) {
h = strdup(e);
if (!h)
return -ENOMEM;
*_h = h;
return 0;
}
/* Hardcode home directory for root and nobody to avoid NSS */
u = getuid();
if (u == 0) {
h = strdup("/root");
if (!h)
return -ENOMEM;
*_h = h;
return 0;
}
if (synthesize_nobody() &&
u == UID_NOBODY) {
h = strdup("/");
if (!h)
return -ENOMEM;
*_h = h;
return 0;
}
/* Check the database... */
errno = 0;
p = getpwuid(u);
if (!p)
return errno > 0 ? -errno : -ESRCH;
if (!path_is_absolute(p->pw_dir))
return -EINVAL;
h = strdup(p->pw_dir);
if (!h)
return -ENOMEM;
*_h = h;
return 0;
}
int get_shell(char **_s) {
struct passwd *p;
const char *e;
char *s;
uid_t u;
assert(_s);
/* Take the user specified one */
e = getenv("SHELL");
if (e) {
s = strdup(e);
if (!s)
return -ENOMEM;
*_s = s;
return 0;
}
/* Hardcode shell for root and nobody to avoid NSS */
u = getuid();
if (u == 0) {
s = strdup("/bin/sh");
if (!s)
return -ENOMEM;
*_s = s;
return 0;
}
if (synthesize_nobody() &&
u == UID_NOBODY) {
s = strdup("/sbin/nologin");
if (!s)
return -ENOMEM;
*_s = s;
return 0;
}
/* Check the database... */
errno = 0;
p = getpwuid(u);
if (!p)
return errno > 0 ? -errno : -ESRCH;
if (!path_is_absolute(p->pw_shell))
return -EINVAL;
s = strdup(p->pw_shell);
if (!s)
return -ENOMEM;
*_s = s;
return 0;
}
int reset_uid_gid(void) {
int r;
r = maybe_setgroups(0, NULL);
if (r < 0)
return r;
if (setresgid(0, 0, 0) < 0)
return -errno;
if (setresuid(0, 0, 0) < 0)
return -errno;
return 0;
}
int take_etc_passwd_lock(const char *root) {
struct flock flock = {
.l_type = F_WRLCK,
.l_whence = SEEK_SET,
.l_start = 0,
.l_len = 0,
};
const char *path;
int fd, r;
/* This is roughly the same as lckpwdf(), but not as awful. We
* don't want to use alarm() and signals, hence we implement
* our own trivial version of this.
*
* Note that shadow-utils also takes per-database locks in
* addition to lckpwdf(). However, we don't given that they
* are redundant as they invoke lckpwdf() first and keep
* it during everything they do. The per-database locks are
* awfully racy, and thus we just won't do them. */
if (root)
path = prefix_roota(root, ETC_PASSWD_LOCK_PATH);
else
path = ETC_PASSWD_LOCK_PATH;
fd = open(path, O_WRONLY|O_CREAT|O_CLOEXEC|O_NOCTTY|O_NOFOLLOW, 0600);
if (fd < 0)
return log_debug_errno(errno, "Cannot open %s: %m", path);
r = fcntl(fd, F_SETLKW, &flock);
if (r < 0) {
safe_close(fd);
return log_debug_errno(errno, "Locking %s failed: %m", path);
}
return fd;
}
bool valid_user_group_name(const char *u) {
const char *i;
long sz;
/* Checks if the specified name is a valid user/group name. Also see POSIX IEEE Std 1003.1-2008, 2016 Edition,
* 3.437. We are a bit stricter here however. Specifically we deviate from POSIX rules:
*
* - We don't allow any dots (this would break chown syntax which permits dots as user/group name separator)
* - We require that names fit into the appropriate utmp field
* - We don't allow empty user names
*
* Note that other systems are even more restrictive, and don't permit underscores or uppercase characters.
*/
if (isempty(u))
return false;
if (!(u[0] >= 'a' && u[0] <= 'z') &&
!(u[0] >= 'A' && u[0] <= 'Z') &&
u[0] != '_')
return false;
for (i = u+1; *i; i++) {
if (!(*i >= 'a' && *i <= 'z') &&
!(*i >= 'A' && *i <= 'Z') &&
!(*i >= '0' && *i <= '9') &&
!IN_SET(*i, '_', '-'))
return false;
}
sz = sysconf(_SC_LOGIN_NAME_MAX);
assert_se(sz > 0);
if ((size_t) (i-u) > (size_t) sz)
return false;
if ((size_t) (i-u) > UT_NAMESIZE - 1)
return false;
return true;
}
bool valid_user_group_name_or_id(const char *u) {
/* Similar as above, but is also fine with numeric UID/GID specifications, as long as they are in the right
* range, and not the invalid user ids. */
if (isempty(u))
return false;
if (valid_user_group_name(u))
return true;
return parse_uid(u, NULL) >= 0;
}
bool valid_gecos(const char *d) {
if (!d)
return false;
if (!utf8_is_valid(d))
return false;
if (string_has_cc(d, NULL))
return false;
/* Colons are used as field separators, and hence not OK */
if (strchr(d, ':'))
return false;
return true;
}
bool valid_home(const char *p) {
/* Note that this function is also called by valid_shell(), any
* changes must account for that. */
if (isempty(p))
return false;
if (!utf8_is_valid(p))
return false;
if (string_has_cc(p, NULL))
return false;
if (!path_is_absolute(p))
return false;
if (!path_is_normalized(p))
return false;
/* Colons are used as field separators, and hence not OK */
if (strchr(p, ':'))
return false;
return true;
}
int maybe_setgroups(size_t size, const gid_t *list) {
int r;
/* Check if setgroups is allowed before we try to drop all the auxiliary groups */
if (size == 0) { /* Dropping all aux groups? */
_cleanup_free_ char *setgroups_content = NULL;
bool can_setgroups;
r = read_one_line_file("/proc/self/setgroups", &setgroups_content);
if (r == -ENOENT)
/* Old kernels don't have /proc/self/setgroups, so assume we can use setgroups */
can_setgroups = true;
else if (r < 0)
return r;
else
can_setgroups = streq(setgroups_content, "allow");
if (!can_setgroups) {
log_debug("Skipping setgroups(), /proc/self/setgroups is set to 'deny'");
return 0;
}
}
if (setgroups(size, list) < 0)
return -errno;
return 0;
}
bool synthesize_nobody(void) {
#ifdef NOLEGACY
return true;
#else
/* Returns true when we shall synthesize the "nobody" user (which we do by default). This can be turned off by
* touching /etc/systemd/dont-synthesize-nobody in order to provide upgrade compatibility with legacy systems
* that used the "nobody" user name and group name for other UIDs/GIDs than 65534.
*
* Note that we do not employ any kind of synchronization on the following caching variable. If the variable is
* accessed in multi-threaded programs in the worst case it might happen that we initialize twice, but that
* shouldn't matter as each initialization should come to the same result. */
static int cache = -1;
if (cache < 0)
cache = access("/etc/systemd/dont-synthesize-nobody", F_OK) < 0;
return cache;
#endif
}
int putpwent_sane(const struct passwd *pw, FILE *stream) {
assert(pw);
assert(stream);
errno = 0;
if (putpwent(pw, stream) != 0)
return errno > 0 ? -errno : -EIO;
return 0;
}
int putspent_sane(const struct spwd *sp, FILE *stream) {
assert(sp);
assert(stream);
errno = 0;
if (putspent(sp, stream) != 0)
return errno > 0 ? -errno : -EIO;
return 0;
}
int putgrent_sane(const struct group *gr, FILE *stream) {
assert(gr);
assert(stream);
errno = 0;
if (putgrent(gr, stream) != 0)
return errno > 0 ? -errno : -EIO;
return 0;
}
#if ENABLE_GSHADOW
int putsgent_sane(const struct sgrp *sg, FILE *stream) {
assert(sg);
assert(stream);
errno = 0;
if (putsgent(sg, stream) != 0)
return errno > 0 ? -errno : -EIO;
return 0;
}
#endif
int fgetpwent_sane(FILE *stream, struct passwd **pw) {
struct passwd *p;
assert(pw);
assert(stream);
errno = 0;
p = fgetpwent(stream);
if (p == NULL) {
if (errno == ENOENT)
return false;
return errno > 0 ? -errno : -EIO;
}
*pw = p;
return true;
}
int fgetspent_sane(FILE *stream, struct spwd **sp) {
struct spwd *s;
assert(sp);
assert(stream);
errno = 0;
s = fgetspent(stream);
if (s == NULL) {
if (errno == ENOENT)
return false;
return errno > 0 ? -errno : -EIO;
}
*sp = s;
return true;
}
int fgetgrent_sane(FILE *stream, struct group **gr) {
struct group *g;
assert(gr);
assert(stream);
errno = 0;
g = fgetgrent(stream);
if (g == NULL) {
if (errno == ENOENT)
return false;
return errno > 0 ? -errno : -EIO;
}
*gr = g;
return true;
}
#if ENABLE_GSHADOW
int fgetsgent_sane(FILE *stream, struct sgrp **sg) {
struct sgrp *s;
assert(sg);
assert(stream);
errno = 0;
s = fgetsgent(stream);
if (s == NULL) {
if (errno == ENOENT)
return false;
return errno > 0 ? -errno : -EIO;
}
*sg = s;
return true;
}
#endif
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