src/shared/capability.c

   1 /*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
   2
   3 /***
   4   This file is part of systemd.
   5
   6   Copyright 2010 Lennart Poettering
   7
   8   systemd is free software; you can redistribute it and/or modify it
   9   under the terms of the GNU Lesser General Public License as published by
  10   the Free Software Foundation; either version 2.1 of the License, or
  11   (at your option) any later version.
  12
  13   systemd is distributed in the hope that it will be useful, but
  14   WITHOUT ANY WARRANTY; without even the implied warranty of
  15   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  16   Lesser General Public License for more details.
  17
  18   You should have received a copy of the GNU Lesser General Public License
  19   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  20 ***/
  21
  22 #include <assert.h>
  23 #include <string.h>
  24 #include <unistd.h>
  25 #include <errno.h>
  26 #include <stdio.h>
  27 #include <sys/types.h>
  28 #include <stdarg.h>
  29 #include <ctype.h>
  30 #include <sys/capability.h>
  31 #include <sys/prctl.h>
  32
  33 #include "macro.h"
  34 #include "capability.h"
  35 #include "util.h"
  36 #include "log.h"
  37 #include "fileio.h"
  38
  39 int have_effective_cap(int value) {
  40         cap_t cap;
  41         cap_flag_value_t fv;
  42         int r;
  43
  44         cap = cap_get_proc();
  45         if (!cap)
  46                 return -errno;
  47
  48         if (cap_get_flag(cap, value, CAP_EFFECTIVE, &fv) < 0)
  49                 r = -errno;
  50         else
  51                 r = fv == CAP_SET;
  52
  53         cap_free(cap);
  54         return r;
  55 }
  56
  57 unsigned long cap_last_cap(void) {
  58         static __thread unsigned long saved;
  59         static __thread bool valid = false;
  60         unsigned long p;
  61
  62         if (valid)
  63                 return saved;
  64
  65         p = (unsigned long) CAP_LAST_CAP;
  66
  67         if (prctl(PR_CAPBSET_READ, p) < 0) {
  68
  69                 /* Hmm, look downwards, until we find one that
  70                  * works */
  71                 for (p--; p > 0; p --)
  72                         if (prctl(PR_CAPBSET_READ, p) >= 0)
  73                                 break;
  74
  75         } else {
  76
  77                 /* Hmm, look upwards, until we find one that doesn't
  78                  * work */
  79                 for (;; p++)
  80                         if (prctl(PR_CAPBSET_READ, p+1) < 0)
  81                                 break;
  82         }
  83
  84         saved = p;
  85         valid = true;
  86
  87         return p;
  88 }
  89
  90 int capability_bounding_set_drop(uint64_t drop, bool right_now) {
  91         unsigned long i;
  92         cap_t after_cap = NULL, temp_cap = NULL;
  93         cap_flag_value_t fv;
  94         int r;
  95
  96         /* If we are run as PID 1 we will lack CAP_SETPCAP by default
  97          * in the effective set (yes, the kernel drops that when
  98          * executing init!), so get it back temporarily so that we can
  99          * call PR_CAPBSET_DROP. */
 100
 101         after_cap = cap_get_proc();
 102         if (!after_cap)
 103                 return -errno;
 104
 105         if (cap_get_flag(after_cap, CAP_SETPCAP, CAP_EFFECTIVE, &fv) < 0) {
 106                 cap_free(after_cap);
 107                 return -errno;
 108         }
 109
 110         if (fv != CAP_SET) {
 111                 static const cap_value_t v = CAP_SETPCAP;
 112
 113                 temp_cap = cap_dup(after_cap);
 114                 if (!temp_cap) {
 115                         r = -errno;
 116                         goto finish;
 117                 }
 118
 119                 if (cap_set_flag(temp_cap, CAP_EFFECTIVE, 1, &v, CAP_SET) < 0) {
 120                         r = -errno;
 121                         goto finish;
 122                 }
 123
 124                 if (cap_set_proc(temp_cap) < 0) {
 125                         r = -errno;
 126                         goto finish;
 127                 }
 128         }
 129
 130         for (i = 0; i <= cap_last_cap(); i++) {
 131
 132                 if (drop & ((uint64_t) 1ULL << (uint64_t) i)) {
 133                         cap_value_t v;
 134
 135                         /* Drop it from the bounding set */
 136                         if (prctl(PR_CAPBSET_DROP, i) < 0) {
 137                                 r = -errno;
 138                                 goto finish;
 139                         }
 140                         v = i;
 141
 142                         /* Also drop it from the inheritable set, so
 143                          * that anything we exec() loses the
 144                          * capability for good. */
 145                         if (cap_set_flag(after_cap, CAP_INHERITABLE, 1, &v, CAP_CLEAR) < 0) {
 146                                 r = -errno;
 147                                 goto finish;
 148                         }
 149
 150                         /* If we shall apply this right now drop it
 151                          * also from our own capability sets. */
 152                         if (right_now) {
 153                                 if (cap_set_flag(after_cap, CAP_PERMITTED, 1, &v, CAP_CLEAR) < 0 ||
 154                                     cap_set_flag(after_cap, CAP_EFFECTIVE, 1, &v, CAP_CLEAR) < 0) {
 155                                         r = -errno;
 156                                         goto finish;
 157                                 }
 158                         }
 159                 }
 160         }
 161
 162         r = 0;
 163
 164 finish:
 165         if (temp_cap)
 166                 cap_free(temp_cap);
 167
 168         if (after_cap) {
 169                 cap_set_proc(after_cap);
 170                 cap_free(after_cap);
 171         }
 172
 173         return r;
 174 }
 175
 176 static int drop_from_file(const char *fn, uint64_t drop) {
 177         int r, k;
 178         uint32_t hi, lo;
 179         uint64_t current, after;
 180         char *p;
 181
 182         r = read_one_line_file(fn, &p);
 183         if (r < 0)
 184                 return r;
 185
 186         assert_cc(sizeof(hi) == sizeof(unsigned));
 187         assert_cc(sizeof(lo) == sizeof(unsigned));
 188
 189         k = sscanf(p, "%u %u", &lo, &hi);
 190         free(p);
 191
 192         if (k != 2)
 193                 return -EIO;
 194
 195         current = (uint64_t) lo | ((uint64_t) hi << 32ULL);
 196         after = current & ~drop;
 197
 198         if (current == after)
 199                 return 0;
 200
 201         lo = (unsigned) (after & 0xFFFFFFFFULL);
 202         hi = (unsigned) ((after >> 32ULL) & 0xFFFFFFFFULL);
 203
 204         if (asprintf(&p, "%u %u", lo, hi) < 0)
 205                 return -ENOMEM;
 206
 207         r = write_string_file(fn, p);
 208         free(p);
 209
 210         return r;
 211 }
 212
 213 int capability_bounding_set_drop_usermode(uint64_t drop) {
 214         int r;
 215
 216         r = drop_from_file("/proc/sys/kernel/usermodehelper/inheritable", drop);
 217         if (r < 0)
 218                 return r;
 219
 220         r = drop_from_file("/proc/sys/kernel/usermodehelper/bset", drop);
 221         if (r < 0)
 222                 return r;
 223
 224         return r;
 225 }