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