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