security/commoncap.c

   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/binfmts.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  */
  44 static 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
  55 int 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  */
  75 int 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  */
 109 int 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  */
 131 int 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;
 145 out:
 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  */
 163 int 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;
 177 out:
 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  */
 192 int 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  */
 211 static 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  */
 235 int 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  */
 271 static 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  */
 288 int 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  */
 310 int 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  */
 324 static 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  */
 366 int 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  */
 422 static 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
 453 out:
 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  */
 469 int 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         }
 506 skip:
 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  */
 574 int 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  */
 603 int 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  */
 630 int 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  */
 674 static 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  */
 697 int 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  */
 745 static 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  */
 766 int 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  */
 779 int 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  */
 792 int 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  */
 801 static 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  */
 824 int 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 */
 918 changed:
 919         return commit_creds(new);
 920
 921 no_change:
 922 error:
 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  */
 935 int 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  */
 959 int 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 }