security/commoncap.c

   1 /* Common capabilities, needed by capability.o and root_plug.o
   2  *
   3  *      This program is free software; you can redistribute it and/or modify
   4  *      it under the terms of the GNU General Public License as published by
   5  *      the Free Software Foundation; either version 2 of the License, or
   6  *      (at your option) any later version.
   7  *
   8  */
   9
  10 #include <linux/capability.h>
  11 #include <linux/config.h>
  12 #include <linux/module.h>
  13 #include <linux/init.h>
  14 #include <linux/kernel.h>
  15 #include <linux/security.h>
  16 #include <linux/file.h>
  17 #include <linux/mm.h>
  18 #include <linux/mman.h>
  19 #include <linux/pagemap.h>
  20 #include <linux/swap.h>
  21 #include <linux/smp_lock.h>
  22 #include <linux/skbuff.h>
  23 #include <linux/netlink.h>
  24 #include <linux/ptrace.h>
  25 #include <linux/xattr.h>
  26 #include <linux/hugetlb.h>
  27
  28 int cap_netlink_send(struct sock *sk, struct sk_buff *skb)
  29 {
  30         NETLINK_CB(skb).eff_cap = current->cap_effective;
  31         return 0;
  32 }
  33
  34 EXPORT_SYMBOL(cap_netlink_send);
  35
  36 int cap_netlink_recv(struct sk_buff *skb)
  37 {
  38         if (!cap_raised(NETLINK_CB(skb).eff_cap, CAP_NET_ADMIN))
  39                 return -EPERM;
  40         return 0;
  41 }
  42
  43 EXPORT_SYMBOL(cap_netlink_recv);
  44
  45 int cap_capable (struct task_struct *tsk, int cap)
  46 {
  47         /* Derived from include/linux/sched.h:capable. */
  48         if (cap_raised(tsk->cap_effective, cap))
  49                 return 0;
  50         return -EPERM;
  51 }
  52
  53 int cap_settime(struct timespec *ts, struct timezone *tz)
  54 {
  55         if (!capable(CAP_SYS_TIME))
  56                 return -EPERM;
  57         return 0;
  58 }
  59
  60 int cap_ptrace (struct task_struct *parent, struct task_struct *child)
  61 {
  62         /* Derived from arch/i386/kernel/ptrace.c:sys_ptrace. */
  63         if (!cap_issubset(child->cap_permitted, parent->cap_permitted) &&
  64             !__capable(parent, CAP_SYS_PTRACE))
  65                 return -EPERM;
  66         return 0;
  67 }
  68
  69 int cap_capget (struct task_struct *target, kernel_cap_t *effective,
  70                 kernel_cap_t *inheritable, kernel_cap_t *permitted)
  71 {
  72         /* Derived from kernel/capability.c:sys_capget. */
  73         *effective = cap_t (target->cap_effective);
  74         *inheritable = cap_t (target->cap_inheritable);
  75         *permitted = cap_t (target->cap_permitted);
  76         return 0;
  77 }
  78
  79 int cap_capset_check (struct task_struct *target, kernel_cap_t *effective,
  80                       kernel_cap_t *inheritable, kernel_cap_t *permitted)
  81 {
  82         /* Derived from kernel/capability.c:sys_capset. */
  83         /* verify restrictions on target's new Inheritable set */
  84         if (!cap_issubset (*inheritable,
  85                            cap_combine (target->cap_inheritable,
  86                                         current->cap_permitted))) {
  87                 return -EPERM;
  88         }
  89
  90         /* verify restrictions on target's new Permitted set */
  91         if (!cap_issubset (*permitted,
  92                            cap_combine (target->cap_permitted,
  93                                         current->cap_permitted))) {
  94                 return -EPERM;
  95         }
  96
  97         /* verify the _new_Effective_ is a subset of the _new_Permitted_ */
  98         if (!cap_issubset (*effective, *permitted)) {
  99                 return -EPERM;
 100         }
 101
 102         return 0;
 103 }
 104
 105 void cap_capset_set (struct task_struct *target, kernel_cap_t *effective,
 106                      kernel_cap_t *inheritable, kernel_cap_t *permitted)
 107 {
 108         target->cap_effective = *effective;
 109         target->cap_inheritable = *inheritable;
 110         target->cap_permitted = *permitted;
 111 }
 112
 113 int cap_bprm_set_security (struct linux_binprm *bprm)
 114 {
 115         /* Copied from fs/exec.c:prepare_binprm. */
 116
 117         /* We don't have VFS support for capabilities yet */
 118         cap_clear (bprm->cap_inheritable);
 119         cap_clear (bprm->cap_permitted);
 120         cap_clear (bprm->cap_effective);
 121
 122         /*  To support inheritance of root-permissions and suid-root
 123          *  executables under compatibility mode, we raise all three
 124          *  capability sets for the file.
 125          *
 126          *  If only the real uid is 0, we only raise the inheritable
 127          *  and permitted sets of the executable file.
 128          */
 129
 130         if (!issecure (SECURE_NOROOT)) {
 131                 if (bprm->e_uid == 0 || current->uid == 0) {
 132                         cap_set_full (bprm->cap_inheritable);
 133                         cap_set_full (bprm->cap_permitted);
 134                 }
 135                 if (bprm->e_uid == 0)
 136                         cap_set_full (bprm->cap_effective);
 137         }
 138         return 0;
 139 }
 140
 141 void cap_bprm_apply_creds (struct linux_binprm *bprm, int unsafe)
 142 {
 143         /* Derived from fs/exec.c:compute_creds. */
 144         kernel_cap_t new_permitted, working;
 145
 146         new_permitted = cap_intersect (bprm->cap_permitted, cap_bset);
 147         working = cap_intersect (bprm->cap_inheritable,
 148                                  current->cap_inheritable);
 149         new_permitted = cap_combine (new_permitted, working);
 150
 151         if (bprm->e_uid != current->uid || bprm->e_gid != current->gid ||
 152             !cap_issubset (new_permitted, current->cap_permitted)) {
 153                 current->mm->dumpable = suid_dumpable;
 154
 155                 if (unsafe & ~LSM_UNSAFE_PTRACE_CAP) {
 156                         if (!capable(CAP_SETUID)) {
 157                                 bprm->e_uid = current->uid;
 158                                 bprm->e_gid = current->gid;
 159                         }
 160                         if (!capable (CAP_SETPCAP)) {
 161                                 new_permitted = cap_intersect (new_permitted,
 162                                                         current->cap_permitted);
 163                         }
 164                 }
 165         }
 166
 167         current->suid = current->euid = current->fsuid = bprm->e_uid;
 168         current->sgid = current->egid = current->fsgid = bprm->e_gid;
 169
 170         /* For init, we want to retain the capabilities set
 171          * in the init_task struct. Thus we skip the usual
 172          * capability rules */
 173         if (current->pid != 1) {
 174                 current->cap_permitted = new_permitted;
 175                 current->cap_effective =
 176                     cap_intersect (new_permitted, bprm->cap_effective);
 177         }
 178
 179         /* AUD: Audit candidate if current->cap_effective is set */
 180
 181         current->keep_capabilities = 0;
 182 }
 183
 184 int cap_bprm_secureexec (struct linux_binprm *bprm)
 185 {
 186         /* If/when this module is enhanced to incorporate capability
 187            bits on files, the test below should be extended to also perform a
 188            test between the old and new capability sets.  For now,
 189            it simply preserves the legacy decision algorithm used by
 190            the old userland. */
 191         return (current->euid != current->uid ||
 192                 current->egid != current->gid);
 193 }
 194
 195 int cap_inode_setxattr(struct dentry *dentry, char *name, void *value,
 196                        size_t size, int flags)
 197 {
 198         if (!strncmp(name, XATTR_SECURITY_PREFIX,
 199                      sizeof(XATTR_SECURITY_PREFIX) - 1)  &&
 200             !capable(CAP_SYS_ADMIN))
 201                 return -EPERM;
 202         return 0;
 203 }
 204
 205 int cap_inode_removexattr(struct dentry *dentry, char *name)
 206 {
 207         if (!strncmp(name, XATTR_SECURITY_PREFIX,
 208                      sizeof(XATTR_SECURITY_PREFIX) - 1)  &&
 209             !capable(CAP_SYS_ADMIN))
 210                 return -EPERM;
 211         return 0;
 212 }
 213
 214 /* moved from kernel/sys.c. */
 215 /*
 216  * cap_emulate_setxuid() fixes the effective / permitted capabilities of
 217  * a process after a call to setuid, setreuid, or setresuid.
 218  *
 219  *  1) When set*uiding _from_ one of {r,e,s}uid == 0 _to_ all of
 220  *  {r,e,s}uid != 0, the permitted and effective capabilities are
 221  *  cleared.
 222  *
 223  *  2) When set*uiding _from_ euid == 0 _to_ euid != 0, the effective
 224  *  capabilities of the process are cleared.
 225  *
 226  *  3) When set*uiding _from_ euid != 0 _to_ euid == 0, the effective
 227  *  capabilities are set to the permitted capabilities.
 228  *
 229  *  fsuid is handled elsewhere. fsuid == 0 and {r,e,s}uid!= 0 should
 230  *  never happen.
 231  *
 232  *  -astor
 233  *
 234  * cevans - New behaviour, Oct '99
 235  * A process may, via prctl(), elect to keep its capabilities when it
 236  * calls setuid() and switches away from uid==0. Both permitted and
 237  * effective sets will be retained.
 238  * Without this change, it was impossible for a daemon to drop only some
 239  * of its privilege. The call to setuid(!=0) would drop all privileges!
 240  * Keeping uid 0 is not an option because uid 0 owns too many vital
 241  * files..
 242  * Thanks to Olaf Kirch and Peter Benie for spotting this.
 243  */
 244 static inline void cap_emulate_setxuid (int old_ruid, int old_euid,
 245                                         int old_suid)
 246 {
 247         if ((old_ruid == 0 || old_euid == 0 || old_suid == 0) &&
 248             (current->uid != 0 && current->euid != 0 && current->suid != 0) &&
 249             !current->keep_capabilities) {
 250                 cap_clear (current->cap_permitted);
 251                 cap_clear (current->cap_effective);
 252         }
 253         if (old_euid == 0 && current->euid != 0) {
 254                 cap_clear (current->cap_effective);
 255         }
 256         if (old_euid != 0 && current->euid == 0) {
 257                 current->cap_effective = current->cap_permitted;
 258         }
 259 }
 260
 261 int cap_task_post_setuid (uid_t old_ruid, uid_t old_euid, uid_t old_suid,
 262                           int flags)
 263 {
 264         switch (flags) {
 265         case LSM_SETID_RE:
 266         case LSM_SETID_ID:
 267         case LSM_SETID_RES:
 268                 /* Copied from kernel/sys.c:setreuid/setuid/setresuid. */
 269                 if (!issecure (SECURE_NO_SETUID_FIXUP)) {
 270                         cap_emulate_setxuid (old_ruid, old_euid, old_suid);
 271                 }
 272                 break;
 273         case LSM_SETID_FS:
 274                 {
 275                         uid_t old_fsuid = old_ruid;
 276
 277                         /* Copied from kernel/sys.c:setfsuid. */
 278
 279                         /*
 280                          * FIXME - is fsuser used for all CAP_FS_MASK capabilities?
 281                          *          if not, we might be a bit too harsh here.
 282                          */
 283
 284                         if (!issecure (SECURE_NO_SETUID_FIXUP)) {
 285                                 if (old_fsuid == 0 && current->fsuid != 0) {
 286                                         cap_t (current->cap_effective) &=
 287                                             ~CAP_FS_MASK;
 288                                 }
 289                                 if (old_fsuid != 0 && current->fsuid == 0) {
 290                                         cap_t (current->cap_effective) |=
 291                                             (cap_t (current->cap_permitted) &
 292                                              CAP_FS_MASK);
 293                                 }
 294                         }
 295                         break;
 296                 }
 297         default:
 298                 return -EINVAL;
 299         }
 300
 301         return 0;
 302 }
 303
 304 void cap_task_reparent_to_init (struct task_struct *p)
 305 {
 306         p->cap_effective = CAP_INIT_EFF_SET;
 307         p->cap_inheritable = CAP_INIT_INH_SET;
 308         p->cap_permitted = CAP_FULL_SET;
 309         p->keep_capabilities = 0;
 310         return;
 311 }
 312
 313 int cap_syslog (int type)
 314 {
 315         if ((type != 3 && type != 10) && !capable(CAP_SYS_ADMIN))
 316                 return -EPERM;
 317         return 0;
 318 }
 319
 320 int cap_vm_enough_memory(long pages)
 321 {
 322         int cap_sys_admin = 0;
 323
 324         if (cap_capable(current, CAP_SYS_ADMIN) == 0)
 325                 cap_sys_admin = 1;
 326         return __vm_enough_memory(pages, cap_sys_admin);
 327 }
 328
 329 EXPORT_SYMBOL(cap_capable);
 330 EXPORT_SYMBOL(cap_settime);
 331 EXPORT_SYMBOL(cap_ptrace);
 332 EXPORT_SYMBOL(cap_capget);
 333 EXPORT_SYMBOL(cap_capset_check);
 334 EXPORT_SYMBOL(cap_capset_set);
 335 EXPORT_SYMBOL(cap_bprm_set_security);
 336 EXPORT_SYMBOL(cap_bprm_apply_creds);
 337 EXPORT_SYMBOL(cap_bprm_secureexec);
 338 EXPORT_SYMBOL(cap_inode_setxattr);
 339 EXPORT_SYMBOL(cap_inode_removexattr);
 340 EXPORT_SYMBOL(cap_task_post_setuid);
 341 EXPORT_SYMBOL(cap_task_reparent_to_init);
 342 EXPORT_SYMBOL(cap_syslog);
 343 EXPORT_SYMBOL(cap_vm_enough_memory);
 344
 345 MODULE_DESCRIPTION("Standard Linux Common Capabilities Security Module");
 346 MODULE_LICENSE("GPL");