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