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         _cleanup_cap_free_ cap_t cap;
  41         cap_flag_value_t fv;
  42
  43         cap = cap_get_proc();
  44         if (!cap)
  45                 return -errno;
  46
  47         if (cap_get_flag(cap, value, CAP_EFFECTIVE, &fv) < 0)
  48                 return -errno;
  49         else
  50                 return fv == CAP_SET;
  51 }
  52
  53 unsigned long cap_last_cap(void) {
  54         static thread_local unsigned long saved;
  55         static thread_local bool valid = false;
  56         unsigned long p;
  57
  58         if (valid)
  59                 return saved;
  60
  61         p = (unsigned long) CAP_LAST_CAP;
  62
  63         if (prctl(PR_CAPBSET_READ, p) < 0) {
  64
  65                 /* Hmm, look downwards, until we find one that
  66                  * works */
  67                 for (p--; p > 0; p --)
  68                         if (prctl(PR_CAPBSET_READ, p) >= 0)
  69                                 break;
  70
  71         } else {
  72
  73                 /* Hmm, look upwards, until we find one that doesn't
  74                  * work */
  75                 for (;; p++)
  76                         if (prctl(PR_CAPBSET_READ, p+1) < 0)
  77                                 break;
  78         }
  79
  80         saved = p;
  81         valid = true;
  82
  83         return p;
  84 }
  85
  86 int capability_bounding_set_drop(uint64_t drop, bool right_now) {
  87         unsigned long i;
  88         _cleanup_cap_free_ cap_t after_cap = NULL, temp_cap = NULL;
  89         cap_flag_value_t fv;
  90         int r;
  91
  92         /* If we are run as PID 1 we will lack CAP_SETPCAP by default
  93          * in the effective set (yes, the kernel drops that when
  94          * executing init!), so get it back temporarily so that we can
  95          * call PR_CAPBSET_DROP. */
  96
  97         after_cap = cap_get_proc();
  98         if (!after_cap)
  99                 return -errno;
 100
 101         if (cap_get_flag(after_cap, CAP_SETPCAP, CAP_EFFECTIVE, &fv) < 0)
 102                 return -errno;
 103
 104         if (fv != CAP_SET) {
 105                 static const cap_value_t v = CAP_SETPCAP;
 106
 107                 temp_cap = cap_dup(after_cap);
 108                 if (!temp_cap) {
 109                         r = -errno;
 110                         goto finish;
 111                 }
 112
 113                 if (cap_set_flag(temp_cap, CAP_EFFECTIVE, 1, &v, CAP_SET) < 0) {
 114                         r = -errno;
 115                         goto finish;
 116                 }
 117
 118                 if (cap_set_proc(temp_cap) < 0) {
 119                         r = -errno;
 120                         goto finish;
 121                 }
 122         }
 123
 124         for (i = 0; i <= cap_last_cap(); i++) {
 125
 126                 if (drop & ((uint64_t) 1ULL << (uint64_t) i)) {
 127                         cap_value_t v;
 128
 129                         /* Drop it from the bounding set */
 130                         if (prctl(PR_CAPBSET_DROP, i) < 0) {
 131                                 r = -errno;
 132                                 goto finish;
 133                         }
 134                         v = (cap_value_t) i;
 135
 136                         /* Also drop it from the inheritable set, so
 137                          * that anything we exec() loses the
 138                          * capability for good. */
 139                         if (cap_set_flag(after_cap, CAP_INHERITABLE, 1, &v, CAP_CLEAR) < 0) {
 140                                 r = -errno;
 141                                 goto finish;
 142                         }
 143
 144                         /* If we shall apply this right now drop it
 145                          * also from our own capability sets. */
 146                         if (right_now) {
 147                                 if (cap_set_flag(after_cap, CAP_PERMITTED, 1, &v, CAP_CLEAR) < 0 ||
 148                                     cap_set_flag(after_cap, CAP_EFFECTIVE, 1, &v, CAP_CLEAR) < 0) {
 149                                         r = -errno;
 150                                         goto finish;
 151                                 }
 152                         }
 153                 }
 154         }
 155
 156         r = 0;
 157
 158 finish:
 159         cap_set_proc(after_cap);
 160
 161         return r;
 162 }
 163
 164 static int drop_from_file(const char *fn, uint64_t drop) {
 165         int r, k;
 166         uint32_t hi, lo;
 167         uint64_t current, after;
 168         char *p;
 169
 170         r = read_one_line_file(fn, &p);
 171         if (r < 0)
 172                 return r;
 173
 174         assert_cc(sizeof(hi) == sizeof(unsigned));
 175         assert_cc(sizeof(lo) == sizeof(unsigned));
 176
 177         k = sscanf(p, "%u %u", &lo, &hi);
 178         free(p);
 179
 180         if (k != 2)
 181                 return -EIO;
 182
 183         current = (uint64_t) lo | ((uint64_t) hi << 32ULL);
 184         after = current & ~drop;
 185
 186         if (current == after)
 187                 return 0;
 188
 189         lo = (unsigned) (after & 0xFFFFFFFFULL);
 190         hi = (unsigned) ((after >> 32ULL) & 0xFFFFFFFFULL);
 191
 192         if (asprintf(&p, "%u %u", lo, hi) < 0)
 193                 return -ENOMEM;
 194
 195         r = write_string_file(fn, p);
 196         free(p);
 197
 198         return r;
 199 }
 200
 201 int capability_bounding_set_drop_usermode(uint64_t drop) {
 202         int r;
 203
 204         r = drop_from_file("/proc/sys/kernel/usermodehelper/inheritable", drop);
 205         if (r < 0)
 206                 return r;
 207
 208         r = drop_from_file("/proc/sys/kernel/usermodehelper/bset", drop);
 209         if (r < 0)
 210                 return r;
 211
 212         return r;
 213 }