1 /* Common capabilities, needed by capability.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/audit.h> 12 #include <linux/module.h> 13 #include <linux/init.h> 14 #include <linux/kernel.h> 15 #include <linux/lsm_hooks.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/skbuff.h> 22 #include <linux/netlink.h> 23 #include <linux/ptrace.h> 24 #include <linux/xattr.h> 25 #include <linux/hugetlb.h> 26 #include <linux/mount.h> 27 #include <linux/sched.h> 28 #include <linux/prctl.h> 29 #include <linux/securebits.h> 30 #include <linux/user_namespace.h> 31 #include <linux/binfmts.h> 32 #include <linux/personality.h> 33 34 /* 35 * If a non-root user executes a setuid-root binary in 36 * !secure(SECURE_NOROOT) mode, then we raise capabilities. 37 * However if fE is also set, then the intent is for only 38 * the file capabilities to be applied, and the setuid-root 39 * bit is left on either to change the uid (plausible) or 40 * to get full privilege on a kernel without file capabilities 41 * support. So in that case we do not raise capabilities. 42 * 43 * Warn if that happens, once per boot. 44 */ 45 static void warn_setuid_and_fcaps_mixed(const char *fname) 46 { 47 static int warned; 48 if (!warned) { 49 printk(KERN_INFO "warning: `%s' has both setuid-root and" 50 " effective capabilities. Therefore not raising all" 51 " capabilities.\n", fname); 52 warned = 1; 53 } 54 } 55 56 /** 57 * cap_capable - Determine whether a task has a particular effective capability 58 * @cred: The credentials to use 59 * @ns: The user namespace in which we need the capability 60 * @cap: The capability to check for 61 * @audit: Whether to write an audit message or not 62 * 63 * Determine whether the nominated task has the specified capability amongst 64 * its effective set, returning 0 if it does, -ve if it does not. 65 * 66 * NOTE WELL: cap_has_capability() cannot be used like the kernel's capable() 67 * and has_capability() functions. That is, it has the reverse semantics: 68 * cap_has_capability() returns 0 when a task has a capability, but the 69 * kernel's capable() and has_capability() returns 1 for this case. 70 */ 71 int cap_capable(const struct cred *cred, struct user_namespace *targ_ns, 72 int cap, int audit) 73 { 74 struct user_namespace *ns = targ_ns; 75 76 /* See if cred has the capability in the target user namespace 77 * by examining the target user namespace and all of the target 78 * user namespace's parents. 79 */ 80 for (;;) { 81 /* Do we have the necessary capabilities? */ 82 if (ns == cred->user_ns) 83 return cap_raised(cred->cap_effective, cap) ? 0 : -EPERM; 84 85 /* Have we tried all of the parent namespaces? */ 86 if (ns == &init_user_ns) 87 return -EPERM; 88 89 /* 90 * The owner of the user namespace in the parent of the 91 * user namespace has all caps. 92 */ 93 if ((ns->parent == cred->user_ns) && uid_eq(ns->owner, cred->euid)) 94 return 0; 95 96 /* 97 * If you have a capability in a parent user ns, then you have 98 * it over all children user namespaces as well. 99 */ 100 ns = ns->parent; 101 } 102 103 /* We never get here */ 104 } 105 106 /** 107 * cap_settime - Determine whether the current process may set the system clock 108 * @ts: The time to set 109 * @tz: The timezone to set 110 * 111 * Determine whether the current process may set the system clock and timezone 112 * information, returning 0 if permission granted, -ve if denied. 113 */ 114 int cap_settime(const struct timespec64 *ts, const struct timezone *tz) 115 { 116 if (!capable(CAP_SYS_TIME)) 117 return -EPERM; 118 return 0; 119 } 120 121 /** 122 * cap_ptrace_access_check - Determine whether the current process may access 123 * another 124 * @child: The process to be accessed 125 * @mode: The mode of attachment. 126 * 127 * If we are in the same or an ancestor user_ns and have all the target 128 * task's capabilities, then ptrace access is allowed. 129 * If we have the ptrace capability to the target user_ns, then ptrace 130 * access is allowed. 131 * Else denied. 132 * 133 * Determine whether a process may access another, returning 0 if permission 134 * granted, -ve if denied. 135 */ 136 int cap_ptrace_access_check(struct task_struct *child, unsigned int mode) 137 { 138 int ret = 0; 139 const struct cred *cred, *child_cred; 140 const kernel_cap_t *caller_caps; 141 142 rcu_read_lock(); 143 cred = current_cred(); 144 child_cred = __task_cred(child); 145 if (mode & PTRACE_MODE_FSCREDS) 146 caller_caps = &cred->cap_effective; 147 else 148 caller_caps = &cred->cap_permitted; 149 if (cred->user_ns == child_cred->user_ns && 150 cap_issubset(child_cred->cap_permitted, *caller_caps)) 151 goto out; 152 if (ns_capable(child_cred->user_ns, CAP_SYS_PTRACE)) 153 goto out; 154 ret = -EPERM; 155 out: 156 rcu_read_unlock(); 157 return ret; 158 } 159 160 /** 161 * cap_ptrace_traceme - Determine whether another process may trace the current 162 * @parent: The task proposed to be the tracer 163 * 164 * If parent is in the same or an ancestor user_ns and has all current's 165 * capabilities, then ptrace access is allowed. 166 * If parent has the ptrace capability to current's user_ns, then ptrace 167 * access is allowed. 168 * Else denied. 169 * 170 * Determine whether the nominated task is permitted to trace the current 171 * process, returning 0 if permission is granted, -ve if denied. 172 */ 173 int cap_ptrace_traceme(struct task_struct *parent) 174 { 175 int ret = 0; 176 const struct cred *cred, *child_cred; 177 178 rcu_read_lock(); 179 cred = __task_cred(parent); 180 child_cred = current_cred(); 181 if (cred->user_ns == child_cred->user_ns && 182 cap_issubset(child_cred->cap_permitted, cred->cap_permitted)) 183 goto out; 184 if (has_ns_capability(parent, child_cred->user_ns, CAP_SYS_PTRACE)) 185 goto out; 186 ret = -EPERM; 187 out: 188 rcu_read_unlock(); 189 return ret; 190 } 191 192 /** 193 * cap_capget - Retrieve a task's capability sets 194 * @target: The task from which to retrieve the capability sets 195 * @effective: The place to record the effective set 196 * @inheritable: The place to record the inheritable set 197 * @permitted: The place to record the permitted set 198 * 199 * This function retrieves the capabilities of the nominated task and returns 200 * them to the caller. 201 */ 202 int cap_capget(struct task_struct *target, kernel_cap_t *effective, 203 kernel_cap_t *inheritable, kernel_cap_t *permitted) 204 { 205 const struct cred *cred; 206 207 /* Derived from kernel/capability.c:sys_capget. */ 208 rcu_read_lock(); 209 cred = __task_cred(target); 210 *effective = cred->cap_effective; 211 *inheritable = cred->cap_inheritable; 212 *permitted = cred->cap_permitted; 213 rcu_read_unlock(); 214 return 0; 215 } 216 217 /* 218 * Determine whether the inheritable capabilities are limited to the old 219 * permitted set. Returns 1 if they are limited, 0 if they are not. 220 */ 221 static inline int cap_inh_is_capped(void) 222 { 223 224 /* they are so limited unless the current task has the CAP_SETPCAP 225 * capability 226 */ 227 if (cap_capable(current_cred(), current_cred()->user_ns, 228 CAP_SETPCAP, SECURITY_CAP_AUDIT) == 0) 229 return 0; 230 return 1; 231 } 232 233 /** 234 * cap_capset - Validate and apply proposed changes to current's capabilities 235 * @new: The proposed new credentials; alterations should be made here 236 * @old: The current task's current credentials 237 * @effective: A pointer to the proposed new effective capabilities set 238 * @inheritable: A pointer to the proposed new inheritable capabilities set 239 * @permitted: A pointer to the proposed new permitted capabilities set 240 * 241 * This function validates and applies a proposed mass change to the current 242 * process's capability sets. The changes are made to the proposed new 243 * credentials, and assuming no error, will be committed by the caller of LSM. 244 */ 245 int cap_capset(struct cred *new, 246 const struct cred *old, 247 const kernel_cap_t *effective, 248 const kernel_cap_t *inheritable, 249 const kernel_cap_t *permitted) 250 { 251 if (cap_inh_is_capped() && 252 !cap_issubset(*inheritable, 253 cap_combine(old->cap_inheritable, 254 old->cap_permitted))) 255 /* incapable of using this inheritable set */ 256 return -EPERM; 257 258 if (!cap_issubset(*inheritable, 259 cap_combine(old->cap_inheritable, 260 old->cap_bset))) 261 /* no new pI capabilities outside bounding set */ 262 return -EPERM; 263 264 /* verify restrictions on target's new Permitted set */ 265 if (!cap_issubset(*permitted, old->cap_permitted)) 266 return -EPERM; 267 268 /* verify the _new_Effective_ is a subset of the _new_Permitted_ */ 269 if (!cap_issubset(*effective, *permitted)) 270 return -EPERM; 271 272 new->cap_effective = *effective; 273 new->cap_inheritable = *inheritable; 274 new->cap_permitted = *permitted; 275 276 /* 277 * Mask off ambient bits that are no longer both permitted and 278 * inheritable. 279 */ 280 new->cap_ambient = cap_intersect(new->cap_ambient, 281 cap_intersect(*permitted, 282 *inheritable)); 283 if (WARN_ON(!cap_ambient_invariant_ok(new))) 284 return -EINVAL; 285 return 0; 286 } 287 288 /* 289 * Clear proposed capability sets for execve(). 290 */ 291 static inline void bprm_clear_caps(struct linux_binprm *bprm) 292 { 293 cap_clear(bprm->cred->cap_permitted); 294 bprm->cap_effective = false; 295 } 296 297 /** 298 * cap_inode_need_killpriv - Determine if inode change affects privileges 299 * @dentry: The inode/dentry in being changed with change marked ATTR_KILL_PRIV 300 * 301 * Determine if an inode having a change applied that's marked ATTR_KILL_PRIV 302 * affects the security markings on that inode, and if it is, should 303 * inode_killpriv() be invoked or the change rejected? 304 * 305 * Returns 0 if granted; +ve if granted, but inode_killpriv() is required; and 306 * -ve to deny the change. 307 */ 308 int cap_inode_need_killpriv(struct dentry *dentry) 309 { 310 struct inode *inode = d_backing_inode(dentry); 311 int error; 312 313 error = __vfs_getxattr(dentry, inode, XATTR_NAME_CAPS, NULL, 0); 314 return error > 0; 315 } 316 317 /** 318 * cap_inode_killpriv - Erase the security markings on an inode 319 * @dentry: The inode/dentry to alter 320 * 321 * Erase the privilege-enhancing security markings on an inode. 322 * 323 * Returns 0 if successful, -ve on error. 324 */ 325 int cap_inode_killpriv(struct dentry *dentry) 326 { 327 int error; 328 329 error = __vfs_removexattr(dentry, XATTR_NAME_CAPS); 330 if (error == -EOPNOTSUPP) 331 error = 0; 332 return error; 333 } 334 335 /* 336 * Calculate the new process capability sets from the capability sets attached 337 * to a file. 338 */ 339 static inline int bprm_caps_from_vfs_caps(struct cpu_vfs_cap_data *caps, 340 struct linux_binprm *bprm, 341 bool *effective, 342 bool *has_cap) 343 { 344 struct cred *new = bprm->cred; 345 unsigned i; 346 int ret = 0; 347 348 if (caps->magic_etc & VFS_CAP_FLAGS_EFFECTIVE) 349 *effective = true; 350 351 if (caps->magic_etc & VFS_CAP_REVISION_MASK) 352 *has_cap = true; 353 354 CAP_FOR_EACH_U32(i) { 355 __u32 permitted = caps->permitted.cap[i]; 356 __u32 inheritable = caps->inheritable.cap[i]; 357 358 /* 359 * pP' = (X & fP) | (pI & fI) 360 * The addition of pA' is handled later. 361 */ 362 new->cap_permitted.cap[i] = 363 (new->cap_bset.cap[i] & permitted) | 364 (new->cap_inheritable.cap[i] & inheritable); 365 366 if (permitted & ~new->cap_permitted.cap[i]) 367 /* insufficient to execute correctly */ 368 ret = -EPERM; 369 } 370 371 /* 372 * For legacy apps, with no internal support for recognizing they 373 * do not have enough capabilities, we return an error if they are 374 * missing some "forced" (aka file-permitted) capabilities. 375 */ 376 return *effective ? ret : 0; 377 } 378 379 /* 380 * Extract the on-exec-apply capability sets for an executable file. 381 */ 382 int get_vfs_caps_from_disk(const struct dentry *dentry, struct cpu_vfs_cap_data *cpu_caps) 383 { 384 struct inode *inode = d_backing_inode(dentry); 385 __u32 magic_etc; 386 unsigned tocopy, i; 387 int size; 388 struct vfs_cap_data caps; 389 390 memset(cpu_caps, 0, sizeof(struct cpu_vfs_cap_data)); 391 392 if (!inode) 393 return -ENODATA; 394 395 size = __vfs_getxattr((struct dentry *)dentry, inode, 396 XATTR_NAME_CAPS, &caps, XATTR_CAPS_SZ); 397 if (size == -ENODATA || size == -EOPNOTSUPP) 398 /* no data, that's ok */ 399 return -ENODATA; 400 if (size < 0) 401 return size; 402 403 if (size < sizeof(magic_etc)) 404 return -EINVAL; 405 406 cpu_caps->magic_etc = magic_etc = le32_to_cpu(caps.magic_etc); 407 408 switch (magic_etc & VFS_CAP_REVISION_MASK) { 409 case VFS_CAP_REVISION_1: 410 if (size != XATTR_CAPS_SZ_1) 411 return -EINVAL; 412 tocopy = VFS_CAP_U32_1; 413 break; 414 case VFS_CAP_REVISION_2: 415 if (size != XATTR_CAPS_SZ_2) 416 return -EINVAL; 417 tocopy = VFS_CAP_U32_2; 418 break; 419 default: 420 return -EINVAL; 421 } 422 423 CAP_FOR_EACH_U32(i) { 424 if (i >= tocopy) 425 break; 426 cpu_caps->permitted.cap[i] = le32_to_cpu(caps.data[i].permitted); 427 cpu_caps->inheritable.cap[i] = le32_to_cpu(caps.data[i].inheritable); 428 } 429 430 cpu_caps->permitted.cap[CAP_LAST_U32] &= CAP_LAST_U32_VALID_MASK; 431 cpu_caps->inheritable.cap[CAP_LAST_U32] &= CAP_LAST_U32_VALID_MASK; 432 433 return 0; 434 } 435 436 /* 437 * Attempt to get the on-exec apply capability sets for an executable file from 438 * its xattrs and, if present, apply them to the proposed credentials being 439 * constructed by execve(). 440 */ 441 static int get_file_caps(struct linux_binprm *bprm, bool *effective, bool *has_cap) 442 { 443 int rc = 0; 444 struct cpu_vfs_cap_data vcaps; 445 446 bprm_clear_caps(bprm); 447 448 if (!file_caps_enabled) 449 return 0; 450 451 if (!mnt_may_suid(bprm->file->f_path.mnt)) 452 return 0; 453 454 /* 455 * This check is redundant with mnt_may_suid() but is kept to make 456 * explicit that capability bits are limited to s_user_ns and its 457 * descendants. 458 */ 459 if (!current_in_userns(bprm->file->f_path.mnt->mnt_sb->s_user_ns)) 460 return 0; 461 462 rc = get_vfs_caps_from_disk(bprm->file->f_path.dentry, &vcaps); 463 if (rc < 0) { 464 if (rc == -EINVAL) 465 printk(KERN_NOTICE "%s: get_vfs_caps_from_disk returned %d for %s\n", 466 __func__, rc, bprm->filename); 467 else if (rc == -ENODATA) 468 rc = 0; 469 goto out; 470 } 471 472 rc = bprm_caps_from_vfs_caps(&vcaps, bprm, effective, has_cap); 473 if (rc == -EINVAL) 474 printk(KERN_NOTICE "%s: cap_from_disk returned %d for %s\n", 475 __func__, rc, bprm->filename); 476 477 out: 478 if (rc) 479 bprm_clear_caps(bprm); 480 481 return rc; 482 } 483 484 /** 485 * cap_bprm_set_creds - Set up the proposed credentials for execve(). 486 * @bprm: The execution parameters, including the proposed creds 487 * 488 * Set up the proposed credentials for a new execution context being 489 * constructed by execve(). The proposed creds in @bprm->cred is altered, 490 * which won't take effect immediately. Returns 0 if successful, -ve on error. 491 */ 492 int cap_bprm_set_creds(struct linux_binprm *bprm) 493 { 494 const struct cred *old = current_cred(); 495 struct cred *new = bprm->cred; 496 bool effective, has_cap = false, is_setid; 497 int ret; 498 kuid_t root_uid; 499 500 if (WARN_ON(!cap_ambient_invariant_ok(old))) 501 return -EPERM; 502 503 effective = false; 504 ret = get_file_caps(bprm, &effective, &has_cap); 505 if (ret < 0) 506 return ret; 507 508 root_uid = make_kuid(new->user_ns, 0); 509 510 if (!issecure(SECURE_NOROOT)) { 511 /* 512 * If the legacy file capability is set, then don't set privs 513 * for a setuid root binary run by a non-root user. Do set it 514 * for a root user just to cause least surprise to an admin. 515 */ 516 if (has_cap && !uid_eq(new->uid, root_uid) && uid_eq(new->euid, root_uid)) { 517 warn_setuid_and_fcaps_mixed(bprm->filename); 518 goto skip; 519 } 520 /* 521 * To support inheritance of root-permissions and suid-root 522 * executables under compatibility mode, we override the 523 * capability sets for the file. 524 * 525 * If only the real uid is 0, we do not set the effective bit. 526 */ 527 if (uid_eq(new->euid, root_uid) || uid_eq(new->uid, root_uid)) { 528 /* pP' = (cap_bset & ~0) | (pI & ~0) */ 529 new->cap_permitted = cap_combine(old->cap_bset, 530 old->cap_inheritable); 531 } 532 if (uid_eq(new->euid, root_uid)) 533 effective = true; 534 } 535 skip: 536 537 /* if we have fs caps, clear dangerous personality flags */ 538 if (!cap_issubset(new->cap_permitted, old->cap_permitted)) 539 bprm->per_clear |= PER_CLEAR_ON_SETID; 540 541 542 /* Don't let someone trace a set[ug]id/setpcap binary with the revised 543 * credentials unless they have the appropriate permit. 544 * 545 * In addition, if NO_NEW_PRIVS, then ensure we get no new privs. 546 */ 547 is_setid = !uid_eq(new->euid, old->uid) || !gid_eq(new->egid, old->gid); 548 549 if ((is_setid || 550 !cap_issubset(new->cap_permitted, old->cap_permitted)) && 551 bprm->unsafe & ~LSM_UNSAFE_PTRACE_CAP) { 552 /* downgrade; they get no more than they had, and maybe less */ 553 if (!capable(CAP_SETUID) || 554 (bprm->unsafe & LSM_UNSAFE_NO_NEW_PRIVS)) { 555 new->euid = new->uid; 556 new->egid = new->gid; 557 } 558 new->cap_permitted = cap_intersect(new->cap_permitted, 559 old->cap_permitted); 560 } 561 562 new->suid = new->fsuid = new->euid; 563 new->sgid = new->fsgid = new->egid; 564 565 /* File caps or setid cancels ambient. */ 566 if (has_cap || is_setid) 567 cap_clear(new->cap_ambient); 568 569 /* 570 * Now that we've computed pA', update pP' to give: 571 * pP' = (X & fP) | (pI & fI) | pA' 572 */ 573 new->cap_permitted = cap_combine(new->cap_permitted, new->cap_ambient); 574 575 /* 576 * Set pE' = (fE ? pP' : pA'). Because pA' is zero if fE is set, 577 * this is the same as pE' = (fE ? pP' : 0) | pA'. 578 */ 579 if (effective) 580 new->cap_effective = new->cap_permitted; 581 else 582 new->cap_effective = new->cap_ambient; 583 584 if (WARN_ON(!cap_ambient_invariant_ok(new))) 585 return -EPERM; 586 587 bprm->cap_effective = effective; 588 589 /* 590 * Audit candidate if current->cap_effective is set 591 * 592 * We do not bother to audit if 3 things are true: 593 * 1) cap_effective has all caps 594 * 2) we are root 595 * 3) root is supposed to have all caps (SECURE_NOROOT) 596 * Since this is just a normal root execing a process. 597 * 598 * Number 1 above might fail if you don't have a full bset, but I think 599 * that is interesting information to audit. 600 */ 601 if (!cap_issubset(new->cap_effective, new->cap_ambient)) { 602 if (!cap_issubset(CAP_FULL_SET, new->cap_effective) || 603 !uid_eq(new->euid, root_uid) || !uid_eq(new->uid, root_uid) || 604 issecure(SECURE_NOROOT)) { 605 ret = audit_log_bprm_fcaps(bprm, new, old); 606 if (ret < 0) 607 return ret; 608 } 609 } 610 611 new->securebits &= ~issecure_mask(SECURE_KEEP_CAPS); 612 613 if (WARN_ON(!cap_ambient_invariant_ok(new))) 614 return -EPERM; 615 616 return 0; 617 } 618 619 /** 620 * cap_bprm_secureexec - Determine whether a secure execution is required 621 * @bprm: The execution parameters 622 * 623 * Determine whether a secure execution is required, return 1 if it is, and 0 624 * if it is not. 625 * 626 * The credentials have been committed by this point, and so are no longer 627 * available through @bprm->cred. 628 */ 629 int cap_bprm_secureexec(struct linux_binprm *bprm) 630 { 631 const struct cred *cred = current_cred(); 632 kuid_t root_uid = make_kuid(cred->user_ns, 0); 633 634 if (!uid_eq(cred->uid, root_uid)) { 635 if (bprm->cap_effective) 636 return 1; 637 if (!cap_issubset(cred->cap_permitted, cred->cap_ambient)) 638 return 1; 639 } 640 641 return (!uid_eq(cred->euid, cred->uid) || 642 !gid_eq(cred->egid, cred->gid)); 643 } 644 645 /** 646 * cap_inode_setxattr - Determine whether an xattr may be altered 647 * @dentry: The inode/dentry being altered 648 * @name: The name of the xattr to be changed 649 * @value: The value that the xattr will be changed to 650 * @size: The size of value 651 * @flags: The replacement flag 652 * 653 * Determine whether an xattr may be altered or set on an inode, returning 0 if 654 * permission is granted, -ve if denied. 655 * 656 * This is used to make sure security xattrs don't get updated or set by those 657 * who aren't privileged to do so. 658 */ 659 int cap_inode_setxattr(struct dentry *dentry, const char *name, 660 const void *value, size_t size, int flags) 661 { 662 if (!strcmp(name, XATTR_NAME_CAPS)) { 663 if (!capable(CAP_SETFCAP)) 664 return -EPERM; 665 return 0; 666 } 667 668 if (!strncmp(name, XATTR_SECURITY_PREFIX, 669 sizeof(XATTR_SECURITY_PREFIX) - 1) && 670 !capable(CAP_SYS_ADMIN)) 671 return -EPERM; 672 return 0; 673 } 674 675 /** 676 * cap_inode_removexattr - Determine whether an xattr may be removed 677 * @dentry: The inode/dentry being altered 678 * @name: The name of the xattr to be changed 679 * 680 * Determine whether an xattr may be removed from an inode, returning 0 if 681 * permission is granted, -ve if denied. 682 * 683 * This is used to make sure security xattrs don't get removed by those who 684 * aren't privileged to remove them. 685 */ 686 int cap_inode_removexattr(struct dentry *dentry, const char *name) 687 { 688 if (!strcmp(name, XATTR_NAME_CAPS)) { 689 if (!capable(CAP_SETFCAP)) 690 return -EPERM; 691 return 0; 692 } 693 694 if (!strncmp(name, XATTR_SECURITY_PREFIX, 695 sizeof(XATTR_SECURITY_PREFIX) - 1) && 696 !capable(CAP_SYS_ADMIN)) 697 return -EPERM; 698 return 0; 699 } 700 701 /* 702 * cap_emulate_setxuid() fixes the effective / permitted capabilities of 703 * a process after a call to setuid, setreuid, or setresuid. 704 * 705 * 1) When set*uiding _from_ one of {r,e,s}uid == 0 _to_ all of 706 * {r,e,s}uid != 0, the permitted and effective capabilities are 707 * cleared. 708 * 709 * 2) When set*uiding _from_ euid == 0 _to_ euid != 0, the effective 710 * capabilities of the process are cleared. 711 * 712 * 3) When set*uiding _from_ euid != 0 _to_ euid == 0, the effective 713 * capabilities are set to the permitted capabilities. 714 * 715 * fsuid is handled elsewhere. fsuid == 0 and {r,e,s}uid!= 0 should 716 * never happen. 717 * 718 * -astor 719 * 720 * cevans - New behaviour, Oct '99 721 * A process may, via prctl(), elect to keep its capabilities when it 722 * calls setuid() and switches away from uid==0. Both permitted and 723 * effective sets will be retained. 724 * Without this change, it was impossible for a daemon to drop only some 725 * of its privilege. The call to setuid(!=0) would drop all privileges! 726 * Keeping uid 0 is not an option because uid 0 owns too many vital 727 * files.. 728 * Thanks to Olaf Kirch and Peter Benie for spotting this. 729 */ 730 static inline void cap_emulate_setxuid(struct cred *new, const struct cred *old) 731 { 732 kuid_t root_uid = make_kuid(old->user_ns, 0); 733 734 if ((uid_eq(old->uid, root_uid) || 735 uid_eq(old->euid, root_uid) || 736 uid_eq(old->suid, root_uid)) && 737 (!uid_eq(new->uid, root_uid) && 738 !uid_eq(new->euid, root_uid) && 739 !uid_eq(new->suid, root_uid))) { 740 if (!issecure(SECURE_KEEP_CAPS)) { 741 cap_clear(new->cap_permitted); 742 cap_clear(new->cap_effective); 743 } 744 745 /* 746 * Pre-ambient programs expect setresuid to nonroot followed 747 * by exec to drop capabilities. We should make sure that 748 * this remains the case. 749 */ 750 cap_clear(new->cap_ambient); 751 } 752 if (uid_eq(old->euid, root_uid) && !uid_eq(new->euid, root_uid)) 753 cap_clear(new->cap_effective); 754 if (!uid_eq(old->euid, root_uid) && uid_eq(new->euid, root_uid)) 755 new->cap_effective = new->cap_permitted; 756 } 757 758 /** 759 * cap_task_fix_setuid - Fix up the results of setuid() call 760 * @new: The proposed credentials 761 * @old: The current task's current credentials 762 * @flags: Indications of what has changed 763 * 764 * Fix up the results of setuid() call before the credential changes are 765 * actually applied, returning 0 to grant the changes, -ve to deny them. 766 */ 767 int cap_task_fix_setuid(struct cred *new, const struct cred *old, int flags) 768 { 769 switch (flags) { 770 case LSM_SETID_RE: 771 case LSM_SETID_ID: 772 case LSM_SETID_RES: 773 /* juggle the capabilities to follow [RES]UID changes unless 774 * otherwise suppressed */ 775 if (!issecure(SECURE_NO_SETUID_FIXUP)) 776 cap_emulate_setxuid(new, old); 777 break; 778 779 case LSM_SETID_FS: 780 /* juggle the capabilties to follow FSUID changes, unless 781 * otherwise suppressed 782 * 783 * FIXME - is fsuser used for all CAP_FS_MASK capabilities? 784 * if not, we might be a bit too harsh here. 785 */ 786 if (!issecure(SECURE_NO_SETUID_FIXUP)) { 787 kuid_t root_uid = make_kuid(old->user_ns, 0); 788 if (uid_eq(old->fsuid, root_uid) && !uid_eq(new->fsuid, root_uid)) 789 new->cap_effective = 790 cap_drop_fs_set(new->cap_effective); 791 792 if (!uid_eq(old->fsuid, root_uid) && uid_eq(new->fsuid, root_uid)) 793 new->cap_effective = 794 cap_raise_fs_set(new->cap_effective, 795 new->cap_permitted); 796 } 797 break; 798 799 default: 800 return -EINVAL; 801 } 802 803 return 0; 804 } 805 806 /* 807 * Rationale: code calling task_setscheduler, task_setioprio, and 808 * task_setnice, assumes that 809 * . if capable(cap_sys_nice), then those actions should be allowed 810 * . if not capable(cap_sys_nice), but acting on your own processes, 811 * then those actions should be allowed 812 * This is insufficient now since you can call code without suid, but 813 * yet with increased caps. 814 * So we check for increased caps on the target process. 815 */ 816 static int cap_safe_nice(struct task_struct *p) 817 { 818 int is_subset, ret = 0; 819 820 rcu_read_lock(); 821 is_subset = cap_issubset(__task_cred(p)->cap_permitted, 822 current_cred()->cap_permitted); 823 if (!is_subset && !ns_capable(__task_cred(p)->user_ns, CAP_SYS_NICE)) 824 ret = -EPERM; 825 rcu_read_unlock(); 826 827 return ret; 828 } 829 830 /** 831 * cap_task_setscheduler - Detemine if scheduler policy change is permitted 832 * @p: The task to affect 833 * 834 * Detemine if the requested scheduler policy change is permitted for the 835 * specified task, returning 0 if permission is granted, -ve if denied. 836 */ 837 int cap_task_setscheduler(struct task_struct *p) 838 { 839 return cap_safe_nice(p); 840 } 841 842 /** 843 * cap_task_ioprio - Detemine if I/O priority change is permitted 844 * @p: The task to affect 845 * @ioprio: The I/O priority to set 846 * 847 * Detemine if the requested I/O priority change is permitted for the specified 848 * task, returning 0 if permission is granted, -ve if denied. 849 */ 850 int cap_task_setioprio(struct task_struct *p, int ioprio) 851 { 852 return cap_safe_nice(p); 853 } 854 855 /** 856 * cap_task_ioprio - Detemine if task priority change is permitted 857 * @p: The task to affect 858 * @nice: The nice value to set 859 * 860 * Detemine if the requested task priority change is permitted for the 861 * specified task, returning 0 if permission is granted, -ve if denied. 862 */ 863 int cap_task_setnice(struct task_struct *p, int nice) 864 { 865 return cap_safe_nice(p); 866 } 867 868 /* 869 * Implement PR_CAPBSET_DROP. Attempt to remove the specified capability from 870 * the current task's bounding set. Returns 0 on success, -ve on error. 871 */ 872 static int cap_prctl_drop(unsigned long cap) 873 { 874 struct cred *new; 875 876 if (!ns_capable(current_user_ns(), CAP_SETPCAP)) 877 return -EPERM; 878 if (!cap_valid(cap)) 879 return -EINVAL; 880 881 new = prepare_creds(); 882 if (!new) 883 return -ENOMEM; 884 cap_lower(new->cap_bset, cap); 885 return commit_creds(new); 886 } 887 888 /** 889 * cap_task_prctl - Implement process control functions for this security module 890 * @option: The process control function requested 891 * @arg2, @arg3, @arg4, @arg5: The argument data for this function 892 * 893 * Allow process control functions (sys_prctl()) to alter capabilities; may 894 * also deny access to other functions not otherwise implemented here. 895 * 896 * Returns 0 or +ve on success, -ENOSYS if this function is not implemented 897 * here, other -ve on error. If -ENOSYS is returned, sys_prctl() and other LSM 898 * modules will consider performing the function. 899 */ 900 int cap_task_prctl(int option, unsigned long arg2, unsigned long arg3, 901 unsigned long arg4, unsigned long arg5) 902 { 903 const struct cred *old = current_cred(); 904 struct cred *new; 905 906 switch (option) { 907 case PR_CAPBSET_READ: 908 if (!cap_valid(arg2)) 909 return -EINVAL; 910 return !!cap_raised(old->cap_bset, arg2); 911 912 case PR_CAPBSET_DROP: 913 return cap_prctl_drop(arg2); 914 915 /* 916 * The next four prctl's remain to assist with transitioning a 917 * system from legacy UID=0 based privilege (when filesystem 918 * capabilities are not in use) to a system using filesystem 919 * capabilities only - as the POSIX.1e draft intended. 920 * 921 * Note: 922 * 923 * PR_SET_SECUREBITS = 924 * issecure_mask(SECURE_KEEP_CAPS_LOCKED) 925 * | issecure_mask(SECURE_NOROOT) 926 * | issecure_mask(SECURE_NOROOT_LOCKED) 927 * | issecure_mask(SECURE_NO_SETUID_FIXUP) 928 * | issecure_mask(SECURE_NO_SETUID_FIXUP_LOCKED) 929 * 930 * will ensure that the current process and all of its 931 * children will be locked into a pure 932 * capability-based-privilege environment. 933 */ 934 case PR_SET_SECUREBITS: 935 if ((((old->securebits & SECURE_ALL_LOCKS) >> 1) 936 & (old->securebits ^ arg2)) /*[1]*/ 937 || ((old->securebits & SECURE_ALL_LOCKS & ~arg2)) /*[2]*/ 938 || (arg2 & ~(SECURE_ALL_LOCKS | SECURE_ALL_BITS)) /*[3]*/ 939 || (cap_capable(current_cred(), 940 current_cred()->user_ns, CAP_SETPCAP, 941 SECURITY_CAP_AUDIT) != 0) /*[4]*/ 942 /* 943 * [1] no changing of bits that are locked 944 * [2] no unlocking of locks 945 * [3] no setting of unsupported bits 946 * [4] doing anything requires privilege (go read about 947 * the "sendmail capabilities bug") 948 */ 949 ) 950 /* cannot change a locked bit */ 951 return -EPERM; 952 953 new = prepare_creds(); 954 if (!new) 955 return -ENOMEM; 956 new->securebits = arg2; 957 return commit_creds(new); 958 959 case PR_GET_SECUREBITS: 960 return old->securebits; 961 962 case PR_GET_KEEPCAPS: 963 return !!issecure(SECURE_KEEP_CAPS); 964 965 case PR_SET_KEEPCAPS: 966 if (arg2 > 1) /* Note, we rely on arg2 being unsigned here */ 967 return -EINVAL; 968 if (issecure(SECURE_KEEP_CAPS_LOCKED)) 969 return -EPERM; 970 971 new = prepare_creds(); 972 if (!new) 973 return -ENOMEM; 974 if (arg2) 975 new->securebits |= issecure_mask(SECURE_KEEP_CAPS); 976 else 977 new->securebits &= ~issecure_mask(SECURE_KEEP_CAPS); 978 return commit_creds(new); 979 980 case PR_CAP_AMBIENT: 981 if (arg2 == PR_CAP_AMBIENT_CLEAR_ALL) { 982 if (arg3 | arg4 | arg5) 983 return -EINVAL; 984 985 new = prepare_creds(); 986 if (!new) 987 return -ENOMEM; 988 cap_clear(new->cap_ambient); 989 return commit_creds(new); 990 } 991 992 if (((!cap_valid(arg3)) | arg4 | arg5)) 993 return -EINVAL; 994 995 if (arg2 == PR_CAP_AMBIENT_IS_SET) { 996 return !!cap_raised(current_cred()->cap_ambient, arg3); 997 } else if (arg2 != PR_CAP_AMBIENT_RAISE && 998 arg2 != PR_CAP_AMBIENT_LOWER) { 999 return -EINVAL; 1000 } else { 1001 if (arg2 == PR_CAP_AMBIENT_RAISE && 1002 (!cap_raised(current_cred()->cap_permitted, arg3) || 1003 !cap_raised(current_cred()->cap_inheritable, 1004 arg3) || 1005 issecure(SECURE_NO_CAP_AMBIENT_RAISE))) 1006 return -EPERM; 1007 1008 new = prepare_creds(); 1009 if (!new) 1010 return -ENOMEM; 1011 if (arg2 == PR_CAP_AMBIENT_RAISE) 1012 cap_raise(new->cap_ambient, arg3); 1013 else 1014 cap_lower(new->cap_ambient, arg3); 1015 return commit_creds(new); 1016 } 1017 1018 default: 1019 /* No functionality available - continue with default */ 1020 return -ENOSYS; 1021 } 1022 } 1023 1024 /** 1025 * cap_vm_enough_memory - Determine whether a new virtual mapping is permitted 1026 * @mm: The VM space in which the new mapping is to be made 1027 * @pages: The size of the mapping 1028 * 1029 * Determine whether the allocation of a new virtual mapping by the current 1030 * task is permitted, returning 1 if permission is granted, 0 if not. 1031 */ 1032 int cap_vm_enough_memory(struct mm_struct *mm, long pages) 1033 { 1034 int cap_sys_admin = 0; 1035 1036 if (cap_capable(current_cred(), &init_user_ns, CAP_SYS_ADMIN, 1037 SECURITY_CAP_NOAUDIT) == 0) 1038 cap_sys_admin = 1; 1039 return cap_sys_admin; 1040 } 1041 1042 /* 1043 * cap_mmap_addr - check if able to map given addr 1044 * @addr: address attempting to be mapped 1045 * 1046 * If the process is attempting to map memory below dac_mmap_min_addr they need 1047 * CAP_SYS_RAWIO. The other parameters to this function are unused by the 1048 * capability security module. Returns 0 if this mapping should be allowed 1049 * -EPERM if not. 1050 */ 1051 int cap_mmap_addr(unsigned long addr) 1052 { 1053 int ret = 0; 1054 1055 if (addr < dac_mmap_min_addr) { 1056 ret = cap_capable(current_cred(), &init_user_ns, CAP_SYS_RAWIO, 1057 SECURITY_CAP_AUDIT); 1058 /* set PF_SUPERPRIV if it turns out we allow the low mmap */ 1059 if (ret == 0) 1060 current->flags |= PF_SUPERPRIV; 1061 } 1062 return ret; 1063 } 1064 1065 int cap_mmap_file(struct file *file, unsigned long reqprot, 1066 unsigned long prot, unsigned long flags) 1067 { 1068 return 0; 1069 } 1070 1071 #ifdef CONFIG_SECURITY 1072 1073 struct security_hook_list capability_hooks[] = { 1074 LSM_HOOK_INIT(capable, cap_capable), 1075 LSM_HOOK_INIT(settime, cap_settime), 1076 LSM_HOOK_INIT(ptrace_access_check, cap_ptrace_access_check), 1077 LSM_HOOK_INIT(ptrace_traceme, cap_ptrace_traceme), 1078 LSM_HOOK_INIT(capget, cap_capget), 1079 LSM_HOOK_INIT(capset, cap_capset), 1080 LSM_HOOK_INIT(bprm_set_creds, cap_bprm_set_creds), 1081 LSM_HOOK_INIT(bprm_secureexec, cap_bprm_secureexec), 1082 LSM_HOOK_INIT(inode_need_killpriv, cap_inode_need_killpriv), 1083 LSM_HOOK_INIT(inode_killpriv, cap_inode_killpriv), 1084 LSM_HOOK_INIT(mmap_addr, cap_mmap_addr), 1085 LSM_HOOK_INIT(mmap_file, cap_mmap_file), 1086 LSM_HOOK_INIT(task_fix_setuid, cap_task_fix_setuid), 1087 LSM_HOOK_INIT(task_prctl, cap_task_prctl), 1088 LSM_HOOK_INIT(task_setscheduler, cap_task_setscheduler), 1089 LSM_HOOK_INIT(task_setioprio, cap_task_setioprio), 1090 LSM_HOOK_INIT(task_setnice, cap_task_setnice), 1091 LSM_HOOK_INIT(vm_enough_memory, cap_vm_enough_memory), 1092 }; 1093 1094 void __init capability_add_hooks(void) 1095 { 1096 security_add_hooks(capability_hooks, ARRAY_SIZE(capability_hooks)); 1097 } 1098 1099 #endif /* CONFIG_SECURITY */ 1100