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 * cap_inode_need_killpriv - Determine if inode change affects privileges 290 * @dentry: The inode/dentry in being changed with change marked ATTR_KILL_PRIV 291 * 292 * Determine if an inode having a change applied that's marked ATTR_KILL_PRIV 293 * affects the security markings on that inode, and if it is, should 294 * inode_killpriv() be invoked or the change rejected? 295 * 296 * Returns 0 if granted; +ve if granted, but inode_killpriv() is required; and 297 * -ve to deny the change. 298 */ 299 int cap_inode_need_killpriv(struct dentry *dentry) 300 { 301 struct inode *inode = d_backing_inode(dentry); 302 int error; 303 304 error = __vfs_getxattr(dentry, inode, XATTR_NAME_CAPS, NULL, 0); 305 return error > 0; 306 } 307 308 /** 309 * cap_inode_killpriv - Erase the security markings on an inode 310 * @dentry: The inode/dentry to alter 311 * 312 * Erase the privilege-enhancing security markings on an inode. 313 * 314 * Returns 0 if successful, -ve on error. 315 */ 316 int cap_inode_killpriv(struct dentry *dentry) 317 { 318 int error; 319 320 error = __vfs_removexattr(dentry, XATTR_NAME_CAPS); 321 if (error == -EOPNOTSUPP) 322 error = 0; 323 return error; 324 } 325 326 /* 327 * Calculate the new process capability sets from the capability sets attached 328 * to a file. 329 */ 330 static inline int bprm_caps_from_vfs_caps(struct cpu_vfs_cap_data *caps, 331 struct linux_binprm *bprm, 332 bool *effective, 333 bool *has_cap) 334 { 335 struct cred *new = bprm->cred; 336 unsigned i; 337 int ret = 0; 338 339 if (caps->magic_etc & VFS_CAP_FLAGS_EFFECTIVE) 340 *effective = true; 341 342 if (caps->magic_etc & VFS_CAP_REVISION_MASK) 343 *has_cap = true; 344 345 CAP_FOR_EACH_U32(i) { 346 __u32 permitted = caps->permitted.cap[i]; 347 __u32 inheritable = caps->inheritable.cap[i]; 348 349 /* 350 * pP' = (X & fP) | (pI & fI) 351 * The addition of pA' is handled later. 352 */ 353 new->cap_permitted.cap[i] = 354 (new->cap_bset.cap[i] & permitted) | 355 (new->cap_inheritable.cap[i] & inheritable); 356 357 if (permitted & ~new->cap_permitted.cap[i]) 358 /* insufficient to execute correctly */ 359 ret = -EPERM; 360 } 361 362 /* 363 * For legacy apps, with no internal support for recognizing they 364 * do not have enough capabilities, we return an error if they are 365 * missing some "forced" (aka file-permitted) capabilities. 366 */ 367 return *effective ? ret : 0; 368 } 369 370 /* 371 * Extract the on-exec-apply capability sets for an executable file. 372 */ 373 int get_vfs_caps_from_disk(const struct dentry *dentry, struct cpu_vfs_cap_data *cpu_caps) 374 { 375 struct inode *inode = d_backing_inode(dentry); 376 __u32 magic_etc; 377 unsigned tocopy, i; 378 int size; 379 struct vfs_cap_data caps; 380 381 memset(cpu_caps, 0, sizeof(struct cpu_vfs_cap_data)); 382 383 if (!inode) 384 return -ENODATA; 385 386 size = __vfs_getxattr((struct dentry *)dentry, inode, 387 XATTR_NAME_CAPS, &caps, XATTR_CAPS_SZ); 388 if (size == -ENODATA || size == -EOPNOTSUPP) 389 /* no data, that's ok */ 390 return -ENODATA; 391 if (size < 0) 392 return size; 393 394 if (size < sizeof(magic_etc)) 395 return -EINVAL; 396 397 cpu_caps->magic_etc = magic_etc = le32_to_cpu(caps.magic_etc); 398 399 switch (magic_etc & VFS_CAP_REVISION_MASK) { 400 case VFS_CAP_REVISION_1: 401 if (size != XATTR_CAPS_SZ_1) 402 return -EINVAL; 403 tocopy = VFS_CAP_U32_1; 404 break; 405 case VFS_CAP_REVISION_2: 406 if (size != XATTR_CAPS_SZ_2) 407 return -EINVAL; 408 tocopy = VFS_CAP_U32_2; 409 break; 410 default: 411 return -EINVAL; 412 } 413 414 CAP_FOR_EACH_U32(i) { 415 if (i >= tocopy) 416 break; 417 cpu_caps->permitted.cap[i] = le32_to_cpu(caps.data[i].permitted); 418 cpu_caps->inheritable.cap[i] = le32_to_cpu(caps.data[i].inheritable); 419 } 420 421 cpu_caps->permitted.cap[CAP_LAST_U32] &= CAP_LAST_U32_VALID_MASK; 422 cpu_caps->inheritable.cap[CAP_LAST_U32] &= CAP_LAST_U32_VALID_MASK; 423 424 return 0; 425 } 426 427 /* 428 * Attempt to get the on-exec apply capability sets for an executable file from 429 * its xattrs and, if present, apply them to the proposed credentials being 430 * constructed by execve(). 431 */ 432 static int get_file_caps(struct linux_binprm *bprm, bool *effective, bool *has_cap) 433 { 434 int rc = 0; 435 struct cpu_vfs_cap_data vcaps; 436 437 cap_clear(bprm->cred->cap_permitted); 438 439 if (!file_caps_enabled) 440 return 0; 441 442 if (!mnt_may_suid(bprm->file->f_path.mnt)) 443 return 0; 444 445 /* 446 * This check is redundant with mnt_may_suid() but is kept to make 447 * explicit that capability bits are limited to s_user_ns and its 448 * descendants. 449 */ 450 if (!current_in_userns(bprm->file->f_path.mnt->mnt_sb->s_user_ns)) 451 return 0; 452 453 rc = get_vfs_caps_from_disk(bprm->file->f_path.dentry, &vcaps); 454 if (rc < 0) { 455 if (rc == -EINVAL) 456 printk(KERN_NOTICE "%s: get_vfs_caps_from_disk returned %d for %s\n", 457 __func__, rc, bprm->filename); 458 else if (rc == -ENODATA) 459 rc = 0; 460 goto out; 461 } 462 463 rc = bprm_caps_from_vfs_caps(&vcaps, bprm, effective, has_cap); 464 if (rc == -EINVAL) 465 printk(KERN_NOTICE "%s: cap_from_disk returned %d for %s\n", 466 __func__, rc, bprm->filename); 467 468 out: 469 if (rc) 470 cap_clear(bprm->cred->cap_permitted); 471 472 return rc; 473 } 474 475 /** 476 * cap_bprm_set_creds - Set up the proposed credentials for execve(). 477 * @bprm: The execution parameters, including the proposed creds 478 * 479 * Set up the proposed credentials for a new execution context being 480 * constructed by execve(). The proposed creds in @bprm->cred is altered, 481 * which won't take effect immediately. Returns 0 if successful, -ve on error. 482 */ 483 int cap_bprm_set_creds(struct linux_binprm *bprm) 484 { 485 const struct cred *old = current_cred(); 486 struct cred *new = bprm->cred; 487 bool effective, has_cap = false, is_setid; 488 int ret; 489 kuid_t root_uid; 490 491 if (WARN_ON(!cap_ambient_invariant_ok(old))) 492 return -EPERM; 493 494 effective = false; 495 ret = get_file_caps(bprm, &effective, &has_cap); 496 if (ret < 0) 497 return ret; 498 499 root_uid = make_kuid(new->user_ns, 0); 500 501 if (!issecure(SECURE_NOROOT)) { 502 /* 503 * If the legacy file capability is set, then don't set privs 504 * for a setuid root binary run by a non-root user. Do set it 505 * for a root user just to cause least surprise to an admin. 506 */ 507 if (has_cap && !uid_eq(new->uid, root_uid) && uid_eq(new->euid, root_uid)) { 508 warn_setuid_and_fcaps_mixed(bprm->filename); 509 goto skip; 510 } 511 /* 512 * To support inheritance of root-permissions and suid-root 513 * executables under compatibility mode, we override the 514 * capability sets for the file. 515 * 516 * If only the real uid is 0, we do not set the effective bit. 517 */ 518 if (uid_eq(new->euid, root_uid) || uid_eq(new->uid, root_uid)) { 519 /* pP' = (cap_bset & ~0) | (pI & ~0) */ 520 new->cap_permitted = cap_combine(old->cap_bset, 521 old->cap_inheritable); 522 } 523 if (uid_eq(new->euid, root_uid)) 524 effective = true; 525 } 526 skip: 527 528 /* if we have fs caps, clear dangerous personality flags */ 529 if (!cap_issubset(new->cap_permitted, old->cap_permitted)) 530 bprm->per_clear |= PER_CLEAR_ON_SETID; 531 532 533 /* Don't let someone trace a set[ug]id/setpcap binary with the revised 534 * credentials unless they have the appropriate permit. 535 * 536 * In addition, if NO_NEW_PRIVS, then ensure we get no new privs. 537 */ 538 is_setid = !uid_eq(new->euid, old->uid) || !gid_eq(new->egid, old->gid); 539 540 if ((is_setid || 541 !cap_issubset(new->cap_permitted, old->cap_permitted)) && 542 ((bprm->unsafe & ~LSM_UNSAFE_PTRACE) || 543 !ptracer_capable(current, new->user_ns))) { 544 /* downgrade; they get no more than they had, and maybe less */ 545 if (!ns_capable(new->user_ns, CAP_SETUID) || 546 (bprm->unsafe & LSM_UNSAFE_NO_NEW_PRIVS)) { 547 new->euid = new->uid; 548 new->egid = new->gid; 549 } 550 new->cap_permitted = cap_intersect(new->cap_permitted, 551 old->cap_permitted); 552 } 553 554 new->suid = new->fsuid = new->euid; 555 new->sgid = new->fsgid = new->egid; 556 557 /* File caps or setid cancels ambient. */ 558 if (has_cap || is_setid) 559 cap_clear(new->cap_ambient); 560 561 /* 562 * Now that we've computed pA', update pP' to give: 563 * pP' = (X & fP) | (pI & fI) | pA' 564 */ 565 new->cap_permitted = cap_combine(new->cap_permitted, new->cap_ambient); 566 567 /* 568 * Set pE' = (fE ? pP' : pA'). Because pA' is zero if fE is set, 569 * this is the same as pE' = (fE ? pP' : 0) | pA'. 570 */ 571 if (effective) 572 new->cap_effective = new->cap_permitted; 573 else 574 new->cap_effective = new->cap_ambient; 575 576 if (WARN_ON(!cap_ambient_invariant_ok(new))) 577 return -EPERM; 578 579 /* 580 * Audit candidate if current->cap_effective is set 581 * 582 * We do not bother to audit if 3 things are true: 583 * 1) cap_effective has all caps 584 * 2) we are root 585 * 3) root is supposed to have all caps (SECURE_NOROOT) 586 * Since this is just a normal root execing a process. 587 * 588 * Number 1 above might fail if you don't have a full bset, but I think 589 * that is interesting information to audit. 590 */ 591 if (!cap_issubset(new->cap_effective, new->cap_ambient)) { 592 if (!cap_issubset(CAP_FULL_SET, new->cap_effective) || 593 !uid_eq(new->euid, root_uid) || !uid_eq(new->uid, root_uid) || 594 issecure(SECURE_NOROOT)) { 595 ret = audit_log_bprm_fcaps(bprm, new, old); 596 if (ret < 0) 597 return ret; 598 } 599 } 600 601 new->securebits &= ~issecure_mask(SECURE_KEEP_CAPS); 602 603 if (WARN_ON(!cap_ambient_invariant_ok(new))) 604 return -EPERM; 605 606 /* Check for privilege-elevated exec. */ 607 bprm->cap_elevated = 0; 608 if (is_setid) { 609 bprm->cap_elevated = 1; 610 } else if (!uid_eq(new->uid, root_uid)) { 611 if (effective || 612 !cap_issubset(new->cap_permitted, new->cap_ambient)) 613 bprm->cap_elevated = 1; 614 } 615 616 return 0; 617 } 618 619 /** 620 * cap_inode_setxattr - Determine whether an xattr may be altered 621 * @dentry: The inode/dentry being altered 622 * @name: The name of the xattr to be changed 623 * @value: The value that the xattr will be changed to 624 * @size: The size of value 625 * @flags: The replacement flag 626 * 627 * Determine whether an xattr may be altered or set on an inode, returning 0 if 628 * permission is granted, -ve if denied. 629 * 630 * This is used to make sure security xattrs don't get updated or set by those 631 * who aren't privileged to do so. 632 */ 633 int cap_inode_setxattr(struct dentry *dentry, const char *name, 634 const void *value, size_t size, int flags) 635 { 636 if (!strcmp(name, XATTR_NAME_CAPS)) { 637 if (!capable(CAP_SETFCAP)) 638 return -EPERM; 639 return 0; 640 } 641 642 if (!strncmp(name, XATTR_SECURITY_PREFIX, 643 sizeof(XATTR_SECURITY_PREFIX) - 1) && 644 !capable(CAP_SYS_ADMIN)) 645 return -EPERM; 646 return 0; 647 } 648 649 /** 650 * cap_inode_removexattr - Determine whether an xattr may be removed 651 * @dentry: The inode/dentry being altered 652 * @name: The name of the xattr to be changed 653 * 654 * Determine whether an xattr may be removed from an inode, returning 0 if 655 * permission is granted, -ve if denied. 656 * 657 * This is used to make sure security xattrs don't get removed by those who 658 * aren't privileged to remove them. 659 */ 660 int cap_inode_removexattr(struct dentry *dentry, const char *name) 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_emulate_setxuid() fixes the effective / permitted capabilities of 677 * a process after a call to setuid, setreuid, or setresuid. 678 * 679 * 1) When set*uiding _from_ one of {r,e,s}uid == 0 _to_ all of 680 * {r,e,s}uid != 0, the permitted and effective capabilities are 681 * cleared. 682 * 683 * 2) When set*uiding _from_ euid == 0 _to_ euid != 0, the effective 684 * capabilities of the process are cleared. 685 * 686 * 3) When set*uiding _from_ euid != 0 _to_ euid == 0, the effective 687 * capabilities are set to the permitted capabilities. 688 * 689 * fsuid is handled elsewhere. fsuid == 0 and {r,e,s}uid!= 0 should 690 * never happen. 691 * 692 * -astor 693 * 694 * cevans - New behaviour, Oct '99 695 * A process may, via prctl(), elect to keep its capabilities when it 696 * calls setuid() and switches away from uid==0. Both permitted and 697 * effective sets will be retained. 698 * Without this change, it was impossible for a daemon to drop only some 699 * of its privilege. The call to setuid(!=0) would drop all privileges! 700 * Keeping uid 0 is not an option because uid 0 owns too many vital 701 * files.. 702 * Thanks to Olaf Kirch and Peter Benie for spotting this. 703 */ 704 static inline void cap_emulate_setxuid(struct cred *new, const struct cred *old) 705 { 706 kuid_t root_uid = make_kuid(old->user_ns, 0); 707 708 if ((uid_eq(old->uid, root_uid) || 709 uid_eq(old->euid, root_uid) || 710 uid_eq(old->suid, root_uid)) && 711 (!uid_eq(new->uid, root_uid) && 712 !uid_eq(new->euid, root_uid) && 713 !uid_eq(new->suid, root_uid))) { 714 if (!issecure(SECURE_KEEP_CAPS)) { 715 cap_clear(new->cap_permitted); 716 cap_clear(new->cap_effective); 717 } 718 719 /* 720 * Pre-ambient programs expect setresuid to nonroot followed 721 * by exec to drop capabilities. We should make sure that 722 * this remains the case. 723 */ 724 cap_clear(new->cap_ambient); 725 } 726 if (uid_eq(old->euid, root_uid) && !uid_eq(new->euid, root_uid)) 727 cap_clear(new->cap_effective); 728 if (!uid_eq(old->euid, root_uid) && uid_eq(new->euid, root_uid)) 729 new->cap_effective = new->cap_permitted; 730 } 731 732 /** 733 * cap_task_fix_setuid - Fix up the results of setuid() call 734 * @new: The proposed credentials 735 * @old: The current task's current credentials 736 * @flags: Indications of what has changed 737 * 738 * Fix up the results of setuid() call before the credential changes are 739 * actually applied, returning 0 to grant the changes, -ve to deny them. 740 */ 741 int cap_task_fix_setuid(struct cred *new, const struct cred *old, int flags) 742 { 743 switch (flags) { 744 case LSM_SETID_RE: 745 case LSM_SETID_ID: 746 case LSM_SETID_RES: 747 /* juggle the capabilities to follow [RES]UID changes unless 748 * otherwise suppressed */ 749 if (!issecure(SECURE_NO_SETUID_FIXUP)) 750 cap_emulate_setxuid(new, old); 751 break; 752 753 case LSM_SETID_FS: 754 /* juggle the capabilties to follow FSUID changes, unless 755 * otherwise suppressed 756 * 757 * FIXME - is fsuser used for all CAP_FS_MASK capabilities? 758 * if not, we might be a bit too harsh here. 759 */ 760 if (!issecure(SECURE_NO_SETUID_FIXUP)) { 761 kuid_t root_uid = make_kuid(old->user_ns, 0); 762 if (uid_eq(old->fsuid, root_uid) && !uid_eq(new->fsuid, root_uid)) 763 new->cap_effective = 764 cap_drop_fs_set(new->cap_effective); 765 766 if (!uid_eq(old->fsuid, root_uid) && uid_eq(new->fsuid, root_uid)) 767 new->cap_effective = 768 cap_raise_fs_set(new->cap_effective, 769 new->cap_permitted); 770 } 771 break; 772 773 default: 774 return -EINVAL; 775 } 776 777 return 0; 778 } 779 780 /* 781 * Rationale: code calling task_setscheduler, task_setioprio, and 782 * task_setnice, assumes that 783 * . if capable(cap_sys_nice), then those actions should be allowed 784 * . if not capable(cap_sys_nice), but acting on your own processes, 785 * then those actions should be allowed 786 * This is insufficient now since you can call code without suid, but 787 * yet with increased caps. 788 * So we check for increased caps on the target process. 789 */ 790 static int cap_safe_nice(struct task_struct *p) 791 { 792 int is_subset, ret = 0; 793 794 rcu_read_lock(); 795 is_subset = cap_issubset(__task_cred(p)->cap_permitted, 796 current_cred()->cap_permitted); 797 if (!is_subset && !ns_capable(__task_cred(p)->user_ns, CAP_SYS_NICE)) 798 ret = -EPERM; 799 rcu_read_unlock(); 800 801 return ret; 802 } 803 804 /** 805 * cap_task_setscheduler - Detemine if scheduler policy change is permitted 806 * @p: The task to affect 807 * 808 * Detemine if the requested scheduler policy change is permitted for the 809 * specified task, returning 0 if permission is granted, -ve if denied. 810 */ 811 int cap_task_setscheduler(struct task_struct *p) 812 { 813 return cap_safe_nice(p); 814 } 815 816 /** 817 * cap_task_ioprio - Detemine if I/O priority change is permitted 818 * @p: The task to affect 819 * @ioprio: The I/O priority to set 820 * 821 * Detemine if the requested I/O priority change is permitted for the specified 822 * task, returning 0 if permission is granted, -ve if denied. 823 */ 824 int cap_task_setioprio(struct task_struct *p, int ioprio) 825 { 826 return cap_safe_nice(p); 827 } 828 829 /** 830 * cap_task_ioprio - Detemine if task priority change is permitted 831 * @p: The task to affect 832 * @nice: The nice value to set 833 * 834 * Detemine if the requested task priority change is permitted for the 835 * specified task, returning 0 if permission is granted, -ve if denied. 836 */ 837 int cap_task_setnice(struct task_struct *p, int nice) 838 { 839 return cap_safe_nice(p); 840 } 841 842 /* 843 * Implement PR_CAPBSET_DROP. Attempt to remove the specified capability from 844 * the current task's bounding set. Returns 0 on success, -ve on error. 845 */ 846 static int cap_prctl_drop(unsigned long cap) 847 { 848 struct cred *new; 849 850 if (!ns_capable(current_user_ns(), CAP_SETPCAP)) 851 return -EPERM; 852 if (!cap_valid(cap)) 853 return -EINVAL; 854 855 new = prepare_creds(); 856 if (!new) 857 return -ENOMEM; 858 cap_lower(new->cap_bset, cap); 859 return commit_creds(new); 860 } 861 862 /** 863 * cap_task_prctl - Implement process control functions for this security module 864 * @option: The process control function requested 865 * @arg2, @arg3, @arg4, @arg5: The argument data for this function 866 * 867 * Allow process control functions (sys_prctl()) to alter capabilities; may 868 * also deny access to other functions not otherwise implemented here. 869 * 870 * Returns 0 or +ve on success, -ENOSYS if this function is not implemented 871 * here, other -ve on error. If -ENOSYS is returned, sys_prctl() and other LSM 872 * modules will consider performing the function. 873 */ 874 int cap_task_prctl(int option, unsigned long arg2, unsigned long arg3, 875 unsigned long arg4, unsigned long arg5) 876 { 877 const struct cred *old = current_cred(); 878 struct cred *new; 879 880 switch (option) { 881 case PR_CAPBSET_READ: 882 if (!cap_valid(arg2)) 883 return -EINVAL; 884 return !!cap_raised(old->cap_bset, arg2); 885 886 case PR_CAPBSET_DROP: 887 return cap_prctl_drop(arg2); 888 889 /* 890 * The next four prctl's remain to assist with transitioning a 891 * system from legacy UID=0 based privilege (when filesystem 892 * capabilities are not in use) to a system using filesystem 893 * capabilities only - as the POSIX.1e draft intended. 894 * 895 * Note: 896 * 897 * PR_SET_SECUREBITS = 898 * issecure_mask(SECURE_KEEP_CAPS_LOCKED) 899 * | issecure_mask(SECURE_NOROOT) 900 * | issecure_mask(SECURE_NOROOT_LOCKED) 901 * | issecure_mask(SECURE_NO_SETUID_FIXUP) 902 * | issecure_mask(SECURE_NO_SETUID_FIXUP_LOCKED) 903 * 904 * will ensure that the current process and all of its 905 * children will be locked into a pure 906 * capability-based-privilege environment. 907 */ 908 case PR_SET_SECUREBITS: 909 if ((((old->securebits & SECURE_ALL_LOCKS) >> 1) 910 & (old->securebits ^ arg2)) /*[1]*/ 911 || ((old->securebits & SECURE_ALL_LOCKS & ~arg2)) /*[2]*/ 912 || (arg2 & ~(SECURE_ALL_LOCKS | SECURE_ALL_BITS)) /*[3]*/ 913 || (cap_capable(current_cred(), 914 current_cred()->user_ns, CAP_SETPCAP, 915 SECURITY_CAP_AUDIT) != 0) /*[4]*/ 916 /* 917 * [1] no changing of bits that are locked 918 * [2] no unlocking of locks 919 * [3] no setting of unsupported bits 920 * [4] doing anything requires privilege (go read about 921 * the "sendmail capabilities bug") 922 */ 923 ) 924 /* cannot change a locked bit */ 925 return -EPERM; 926 927 new = prepare_creds(); 928 if (!new) 929 return -ENOMEM; 930 new->securebits = arg2; 931 return commit_creds(new); 932 933 case PR_GET_SECUREBITS: 934 return old->securebits; 935 936 case PR_GET_KEEPCAPS: 937 return !!issecure(SECURE_KEEP_CAPS); 938 939 case PR_SET_KEEPCAPS: 940 if (arg2 > 1) /* Note, we rely on arg2 being unsigned here */ 941 return -EINVAL; 942 if (issecure(SECURE_KEEP_CAPS_LOCKED)) 943 return -EPERM; 944 945 new = prepare_creds(); 946 if (!new) 947 return -ENOMEM; 948 if (arg2) 949 new->securebits |= issecure_mask(SECURE_KEEP_CAPS); 950 else 951 new->securebits &= ~issecure_mask(SECURE_KEEP_CAPS); 952 return commit_creds(new); 953 954 case PR_CAP_AMBIENT: 955 if (arg2 == PR_CAP_AMBIENT_CLEAR_ALL) { 956 if (arg3 | arg4 | arg5) 957 return -EINVAL; 958 959 new = prepare_creds(); 960 if (!new) 961 return -ENOMEM; 962 cap_clear(new->cap_ambient); 963 return commit_creds(new); 964 } 965 966 if (((!cap_valid(arg3)) | arg4 | arg5)) 967 return -EINVAL; 968 969 if (arg2 == PR_CAP_AMBIENT_IS_SET) { 970 return !!cap_raised(current_cred()->cap_ambient, arg3); 971 } else if (arg2 != PR_CAP_AMBIENT_RAISE && 972 arg2 != PR_CAP_AMBIENT_LOWER) { 973 return -EINVAL; 974 } else { 975 if (arg2 == PR_CAP_AMBIENT_RAISE && 976 (!cap_raised(current_cred()->cap_permitted, arg3) || 977 !cap_raised(current_cred()->cap_inheritable, 978 arg3) || 979 issecure(SECURE_NO_CAP_AMBIENT_RAISE))) 980 return -EPERM; 981 982 new = prepare_creds(); 983 if (!new) 984 return -ENOMEM; 985 if (arg2 == PR_CAP_AMBIENT_RAISE) 986 cap_raise(new->cap_ambient, arg3); 987 else 988 cap_lower(new->cap_ambient, arg3); 989 return commit_creds(new); 990 } 991 992 default: 993 /* No functionality available - continue with default */ 994 return -ENOSYS; 995 } 996 } 997 998 /** 999 * cap_vm_enough_memory - Determine whether a new virtual mapping is permitted 1000 * @mm: The VM space in which the new mapping is to be made 1001 * @pages: The size of the mapping 1002 * 1003 * Determine whether the allocation of a new virtual mapping by the current 1004 * task is permitted, returning 1 if permission is granted, 0 if not. 1005 */ 1006 int cap_vm_enough_memory(struct mm_struct *mm, long pages) 1007 { 1008 int cap_sys_admin = 0; 1009 1010 if (cap_capable(current_cred(), &init_user_ns, CAP_SYS_ADMIN, 1011 SECURITY_CAP_NOAUDIT) == 0) 1012 cap_sys_admin = 1; 1013 return cap_sys_admin; 1014 } 1015 1016 /* 1017 * cap_mmap_addr - check if able to map given addr 1018 * @addr: address attempting to be mapped 1019 * 1020 * If the process is attempting to map memory below dac_mmap_min_addr they need 1021 * CAP_SYS_RAWIO. The other parameters to this function are unused by the 1022 * capability security module. Returns 0 if this mapping should be allowed 1023 * -EPERM if not. 1024 */ 1025 int cap_mmap_addr(unsigned long addr) 1026 { 1027 int ret = 0; 1028 1029 if (addr < dac_mmap_min_addr) { 1030 ret = cap_capable(current_cred(), &init_user_ns, CAP_SYS_RAWIO, 1031 SECURITY_CAP_AUDIT); 1032 /* set PF_SUPERPRIV if it turns out we allow the low mmap */ 1033 if (ret == 0) 1034 current->flags |= PF_SUPERPRIV; 1035 } 1036 return ret; 1037 } 1038 1039 int cap_mmap_file(struct file *file, unsigned long reqprot, 1040 unsigned long prot, unsigned long flags) 1041 { 1042 return 0; 1043 } 1044 1045 #ifdef CONFIG_SECURITY 1046 1047 struct security_hook_list capability_hooks[] __lsm_ro_after_init = { 1048 LSM_HOOK_INIT(capable, cap_capable), 1049 LSM_HOOK_INIT(settime, cap_settime), 1050 LSM_HOOK_INIT(ptrace_access_check, cap_ptrace_access_check), 1051 LSM_HOOK_INIT(ptrace_traceme, cap_ptrace_traceme), 1052 LSM_HOOK_INIT(capget, cap_capget), 1053 LSM_HOOK_INIT(capset, cap_capset), 1054 LSM_HOOK_INIT(bprm_set_creds, cap_bprm_set_creds), 1055 LSM_HOOK_INIT(inode_need_killpriv, cap_inode_need_killpriv), 1056 LSM_HOOK_INIT(inode_killpriv, cap_inode_killpriv), 1057 LSM_HOOK_INIT(mmap_addr, cap_mmap_addr), 1058 LSM_HOOK_INIT(mmap_file, cap_mmap_file), 1059 LSM_HOOK_INIT(task_fix_setuid, cap_task_fix_setuid), 1060 LSM_HOOK_INIT(task_prctl, cap_task_prctl), 1061 LSM_HOOK_INIT(task_setscheduler, cap_task_setscheduler), 1062 LSM_HOOK_INIT(task_setioprio, cap_task_setioprio), 1063 LSM_HOOK_INIT(task_setnice, cap_task_setnice), 1064 LSM_HOOK_INIT(vm_enough_memory, cap_vm_enough_memory), 1065 }; 1066 1067 void __init capability_add_hooks(void) 1068 { 1069 security_add_hooks(capability_hooks, ARRAY_SIZE(capability_hooks), 1070 "capability"); 1071 } 1072 1073 #endif /* CONFIG_SECURITY */ 1074