/***
This file is part of systemd.
Copyright 2010 Lennart Poettering
systemd is free software; you can redistribute it and/or modify it
under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or
(at your option) any later version.
systemd is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with systemd; If not, see <http://www.gnu.org/licenses/>.
***/
#include <errno.h>
#include <grp.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/capability.h>
#include <sys/prctl.h>
#include <unistd.h>
#include "alloc-util.h"
#include "capability-util.h"
#include "fileio.h"
#include "log.h"
#include "macro.h"
#include "parse-util.h"
#include "util.h"
int have_effective_cap(int value) {
_cleanup_cap_free_ cap_t cap;
cap_flag_value_t fv;
cap = cap_get_proc();
if (!cap)
return -errno;
if (cap_get_flag(cap, value, CAP_EFFECTIVE, &fv) < 0)
return -errno;
else
return fv == CAP_SET;
}
unsigned long cap_last_cap(void) {
static thread_local unsigned long saved;
static thread_local bool valid = false;
_cleanup_free_ char *content = NULL;
unsigned long p = 0;
int r;
if (valid)
return saved;
/* available since linux-3.2 */
r = read_one_line_file("/proc/sys/kernel/cap_last_cap", &content);
if (r >= 0) {
r = safe_atolu(content, &p);
if (r >= 0) {
saved = p;
valid = true;
return p;
}
}
/* fall back to syscall-probing for pre linux-3.2 */
p = (unsigned long) CAP_LAST_CAP;
if (prctl(PR_CAPBSET_READ, p) < 0) {
/* Hmm, look downwards, until we find one that
* works */
for (p--; p > 0; p --)
if (prctl(PR_CAPBSET_READ, p) >= 0)
break;
} else {
/* Hmm, look upwards, until we find one that doesn't
* work */
for (;; p++)
if (prctl(PR_CAPBSET_READ, p+1) < 0)
break;
}
saved = p;
valid = true;
return p;
}
int capability_update_inherited_set(cap_t caps, uint64_t set) {
unsigned long i;
/* Add capabilities in the set to the inherited caps. Do not apply
* them yet. */
for (i = 0; i < cap_last_cap(); i++) {
if (set & (UINT64_C(1) << i)) {
cap_value_t v;
v = (cap_value_t) i;
/* Make the capability inheritable. */
if (cap_set_flag(caps, CAP_INHERITABLE, 1, &v, CAP_SET) < 0)
return -errno;
}
}
return 0;
}
int capability_ambient_set_apply(uint64_t set, bool also_inherit) {
unsigned long i;
_cleanup_cap_free_ cap_t caps = NULL;
/* Add the capabilities to the ambient set. */
if (also_inherit) {
int r;
caps = cap_get_proc();
if (!caps)
return -errno;
r = capability_update_inherited_set(caps, set);
if (r < 0)
return -errno;
if (cap_set_proc(caps) < 0)
return -errno;
}
for (i = 0; i < cap_last_cap(); i++) {
if (set & (UINT64_C(1) << i)) {
/* Add the capability to the ambient set. */
if (prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_RAISE, i, 0, 0) < 0)
return -errno;
}
}
return 0;
}
int capability_bounding_set_drop(uint64_t keep, bool right_now) {
_cleanup_cap_free_ cap_t after_cap = NULL;
cap_flag_value_t fv;
unsigned long i;
int r;
/* If we are run as PID 1 we will lack CAP_SETPCAP by default
* in the effective set (yes, the kernel drops that when
* executing init!), so get it back temporarily so that we can
* call PR_CAPBSET_DROP. */
after_cap = cap_get_proc();
if (!after_cap)
return -errno;
if (cap_get_flag(after_cap, CAP_SETPCAP, CAP_EFFECTIVE, &fv) < 0)
return -errno;
if (fv != CAP_SET) {
_cleanup_cap_free_ cap_t temp_cap = NULL;
static const cap_value_t v = CAP_SETPCAP;
temp_cap = cap_dup(after_cap);
if (!temp_cap) {
r = -errno;
goto finish;
}
if (cap_set_flag(temp_cap, CAP_EFFECTIVE, 1, &v, CAP_SET) < 0) {
r = -errno;
goto finish;
}
if (cap_set_proc(temp_cap) < 0) {
r = -errno;
goto finish;
}
}
for (i = 0; i <= cap_last_cap(); i++) {
if (!(keep & (UINT64_C(1) << i))) {
cap_value_t v;
/* Drop it from the bounding set */
if (prctl(PR_CAPBSET_DROP, i) < 0) {
r = -errno;
goto finish;
}
v = (cap_value_t) i;
/* Also drop it from the inheritable set, so
* that anything we exec() loses the
* capability for good. */
if (cap_set_flag(after_cap, CAP_INHERITABLE, 1, &v, CAP_CLEAR) < 0) {
r = -errno;
goto finish;
}
/* If we shall apply this right now drop it
* also from our own capability sets. */
if (right_now) {
if (cap_set_flag(after_cap, CAP_PERMITTED, 1, &v, CAP_CLEAR) < 0 ||
cap_set_flag(after_cap, CAP_EFFECTIVE, 1, &v, CAP_CLEAR) < 0) {
r = -errno;
goto finish;
}
}
}
}
r = 0;
finish:
if (cap_set_proc(after_cap) < 0)
return -errno;
return r;
}
static int drop_from_file(const char *fn, uint64_t keep) {
int r, k;
uint32_t hi, lo;
uint64_t current, after;
char *p;
r = read_one_line_file(fn, &p);
if (r < 0)
return r;
assert_cc(sizeof(hi) == sizeof(unsigned));
assert_cc(sizeof(lo) == sizeof(unsigned));
k = sscanf(p, "%u %u", &lo, &hi);
free(p);
if (k != 2)
return -EIO;
current = (uint64_t) lo | ((uint64_t) hi << 32ULL);
after = current & keep;
if (current == after)
return 0;
lo = (unsigned) (after & 0xFFFFFFFFULL);
hi = (unsigned) ((after >> 32ULL) & 0xFFFFFFFFULL);
if (asprintf(&p, "%u %u", lo, hi) < 0)
return -ENOMEM;
r = write_string_file(fn, p, WRITE_STRING_FILE_CREATE);
free(p);
return r;
}
int capability_bounding_set_drop_usermode(uint64_t keep) {
int r;
r = drop_from_file("/proc/sys/kernel/usermodehelper/inheritable", keep);
if (r < 0)
return r;
r = drop_from_file("/proc/sys/kernel/usermodehelper/bset", keep);
if (r < 0)
return r;
return r;
}
int drop_privileges(uid_t uid, gid_t gid, uint64_t keep_capabilities) {
_cleanup_cap_free_ cap_t d = NULL;
unsigned i, j = 0;
int r;
/* Unfortunately we cannot leave privilege dropping to PID 1
* here, since we want to run as user but want to keep some
* capabilities. Since file capabilities have been introduced
* this cannot be done across exec() anymore, unless our
* binary has the capability configured in the file system,
* which we want to avoid. */
if (setresgid(gid, gid, gid) < 0)
return log_error_errno(errno, "Failed to change group ID: %m");
if (setgroups(0, NULL) < 0)
return log_error_errno(errno, "Failed to drop auxiliary groups list: %m");
/* Ensure we keep the permitted caps across the setresuid() */
if (prctl(PR_SET_KEEPCAPS, 1) < 0)
return log_error_errno(errno, "Failed to enable keep capabilities flag: %m");
r = setresuid(uid, uid, uid);
if (r < 0)
return log_error_errno(errno, "Failed to change user ID: %m");
if (prctl(PR_SET_KEEPCAPS, 0) < 0)
return log_error_errno(errno, "Failed to disable keep capabilities flag: %m");
/* Drop all caps from the bounding set, except the ones we want */
r = capability_bounding_set_drop(keep_capabilities, true);
if (r < 0)
return log_error_errno(r, "Failed to drop capabilities: %m");
/* Now upgrade the permitted caps we still kept to effective caps */
d = cap_init();
if (!d)
return log_oom();
if (keep_capabilities) {
cap_value_t bits[u64log2(keep_capabilities) + 1];
for (i = 0; i < ELEMENTSOF(bits); i++)
if (keep_capabilities & (1ULL << i))
bits[j++] = i;
/* use enough bits */
assert(i == 64 || (keep_capabilities >> i) == 0);
/* don't use too many bits */
assert(keep_capabilities & (1ULL << (i - 1)));
if (cap_set_flag(d, CAP_EFFECTIVE, j, bits, CAP_SET) < 0 ||
cap_set_flag(d, CAP_PERMITTED, j, bits, CAP_SET) < 0)
return log_error_errno(errno, "Failed to enable capabilities bits: %m");
if (cap_set_proc(d) < 0)
return log_error_errno(errno, "Failed to increase capabilities: %m");
}
return 0;
}
int drop_capability(cap_value_t cv) {
_cleanup_cap_free_ cap_t tmp_cap = NULL;
tmp_cap = cap_get_proc();
if (!tmp_cap)
return -errno;
if ((cap_set_flag(tmp_cap, CAP_INHERITABLE, 1, &cv, CAP_CLEAR) < 0) ||
(cap_set_flag(tmp_cap, CAP_PERMITTED, 1, &cv, CAP_CLEAR) < 0) ||
(cap_set_flag(tmp_cap, CAP_EFFECTIVE, 1, &cv, CAP_CLEAR) < 0))
return -errno;
if (cap_set_proc(tmp_cap) < 0)
return -errno;
return 0;
}