capability.c revision 574d5f2dfc25226afc718aa5ba1a145fe5cad221
/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
/***
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 <assert.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <stdio.h>
#include <sys/types.h>
#include <stdarg.h>
#include <ctype.h>
#include <sys/capability.h>
#include <sys/prctl.h>
#include "macro.h"
#include "capability.h"
#include "util.h"
#include "log.h"
#include "fileio.h"
int have_effective_cap(int value) {
cap_t cap;
cap_flag_value_t fv;
int r;
cap = cap_get_proc();
if (!cap)
return -errno;
if (cap_get_flag(cap, value, CAP_EFFECTIVE, &fv) < 0)
r = -errno;
else
r = fv == CAP_SET;
cap_free(cap);
return r;
}
unsigned long cap_last_cap(void) {
static __thread unsigned long saved;
static __thread bool valid = false;
unsigned long p;
if (valid)
return saved;
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_bounding_set_drop(uint64_t drop, bool right_now) {
unsigned long i;
cap_t after_cap = NULL, temp_cap = NULL;
cap_flag_value_t fv;
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) {
cap_free(after_cap);
return -errno;
}
if (fv != CAP_SET) {
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 (drop & ((uint64_t) 1ULL << (uint64_t) i)) {
cap_value_t v;
/* Drop it from the bounding set */
if (prctl(PR_CAPBSET_DROP, i) < 0) {
r = -errno;
goto finish;
}
v = 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 (temp_cap)
cap_free(temp_cap);
if (after_cap) {
cap_set_proc(after_cap);
cap_free(after_cap);
}
return r;
}
static int drop_from_file(const char *fn, uint64_t drop) {
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 & ~drop;
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);
free(p);
return r;
}
int capability_bounding_set_drop_usermode(uint64_t drop) {
int r;
r = drop_from_file("/proc/sys/kernel/usermodehelper/inheritable", drop);
if (r < 0)
return r;
r = drop_from_file("/proc/sys/kernel/usermodehelper/bset", drop);
if (r < 0)
return r;
return r;
}