kernel/capability.c

   1 /*
   2  * linux/kernel/capability.c
   3  *
   4  * Copyright (C) 1997  Andrew Main <zefram@fysh.org>
   5  *
   6  * Integrated into 2.1.97+,  Andrew G. Morgan <morgan@kernel.org>
   7  * 30 May 2002: Cleanup, Robert M. Love <rml@tech9.net>
   8  */
   9
  10 #include <linux/capability.h>
  11 #include <linux/mm.h>
  12 #include <linux/module.h>
  13 #include <linux/security.h>
  14 #include <linux/syscalls.h>
  15 #include <linux/pid_namespace.h>
  16 #include <asm/uaccess.h>
  17
  18 /*
  19  * This lock protects task->cap_* for all tasks including current.
  20  * Locking rule: acquire this prior to tasklist_lock.
  21  */
  22 static DEFINE_SPINLOCK(task_capability_lock);
  23
  24 /*
  25  * Leveraged for setting/resetting capabilities
  26  */
  27
  28 const kernel_cap_t __cap_empty_set = CAP_EMPTY_SET;
  29 const kernel_cap_t __cap_full_set = CAP_FULL_SET;
  30 const kernel_cap_t __cap_init_eff_set = CAP_INIT_EFF_SET;
  31
  32 EXPORT_SYMBOL(__cap_empty_set);
  33 EXPORT_SYMBOL(__cap_full_set);
  34 EXPORT_SYMBOL(__cap_init_eff_set);
  35
  36 /*
  37  * More recent versions of libcap are available from:
  38  *
  39  *   http://www.kernel.org/pub/linux/libs/security/linux-privs/
  40  */
  41
  42 static void warn_legacy_capability_use(void)
  43 {
  44         static int warned;
  45         if (!warned) {
  46                 char name[sizeof(current->comm)];
  47
  48                 printk(KERN_INFO "warning: `%s' uses 32-bit capabilities"
  49                        " (legacy support in use)\n",
  50                        get_task_comm(name, current));
  51                 warned = 1;
  52         }
  53 }
  54
  55 /*
  56  * Version 2 capabilities worked fine, but the linux/capability.h file
  57  * that accompanied their introduction encouraged their use without
  58  * the necessary user-space source code changes. As such, we have
  59  * created a version 3 with equivalent functionality to version 2, but
  60  * with a header change to protect legacy source code from using
  61  * version 2 when it wanted to use version 1. If your system has code
  62  * that trips the following warning, it is using version 2 specific
  63  * capabilities and may be doing so insecurely.
  64  *
  65  * The remedy is to either upgrade your version of libcap (to 2.10+,
  66  * if the application is linked against it), or recompile your
  67  * application with modern kernel headers and this warning will go
  68  * away.
  69  */
  70
  71 static void warn_deprecated_v2(void)
  72 {
  73         static int warned;
  74
  75         if (!warned) {
  76                 char name[sizeof(current->comm)];
  77
  78                 printk(KERN_INFO "warning: `%s' uses deprecated v2"
  79                        " capabilities in a way that may be insecure.\n",
  80                        get_task_comm(name, current));
  81                 warned = 1;
  82         }
  83 }
  84
  85 /*
  86  * Version check. Return the number of u32s in each capability flag
  87  * array, or a negative value on error.
  88  */
  89 static int cap_validate_magic(cap_user_header_t header, unsigned *tocopy)
  90 {
  91         __u32 version;
  92
  93         if (get_user(version, &header->version))
  94                 return -EFAULT;
  95
  96         switch (version) {
  97         case _LINUX_CAPABILITY_VERSION_1:
  98                 warn_legacy_capability_use();
  99                 *tocopy = _LINUX_CAPABILITY_U32S_1;
 100                 break;
 101         case _LINUX_CAPABILITY_VERSION_2:
 102                 warn_deprecated_v2();
 103                 /*
 104                  * fall through - v3 is otherwise equivalent to v2.
 105                  */
 106         case _LINUX_CAPABILITY_VERSION_3:
 107                 *tocopy = _LINUX_CAPABILITY_U32S_3;
 108                 break;
 109         default:
 110                 if (put_user((u32)_KERNEL_CAPABILITY_VERSION, &header->version))
 111                         return -EFAULT;
 112                 return -EINVAL;
 113         }
 114
 115         return 0;
 116 }
 117
 118 #ifndef CONFIG_SECURITY_FILE_CAPABILITIES
 119
 120 /*
 121  * Without filesystem capability support, we nominally support one process
 122  * setting the capabilities of another
 123  */
 124 static inline int cap_get_target_pid(pid_t pid, kernel_cap_t *pEp,
 125                                      kernel_cap_t *pIp, kernel_cap_t *pPp)
 126 {
 127         struct task_struct *target;
 128         int ret;
 129
 130         spin_lock(&task_capability_lock);
 131         read_lock(&tasklist_lock);
 132
 133         if (pid && pid != task_pid_vnr(current)) {
 134                 target = find_task_by_vpid(pid);
 135                 if (!target) {
 136                         ret = -ESRCH;
 137                         goto out;
 138                 }
 139         } else
 140                 target = current;
 141
 142         ret = security_capget(target, pEp, pIp, pPp);
 143
 144 out:
 145         read_unlock(&tasklist_lock);
 146         spin_unlock(&task_capability_lock);
 147
 148         return ret;
 149 }
 150
 151 /*
 152  * cap_set_pg - set capabilities for all processes in a given process
 153  * group.  We call this holding task_capability_lock and tasklist_lock.
 154  */
 155 static inline int cap_set_pg(int pgrp_nr, kernel_cap_t *effective,
 156                              kernel_cap_t *inheritable,
 157                              kernel_cap_t *permitted)
 158 {
 159         struct task_struct *g, *target;
 160         int ret = -EPERM;
 161         int found = 0;
 162         struct pid *pgrp;
 163
 164         spin_lock(&task_capability_lock);
 165         read_lock(&tasklist_lock);
 166
 167         pgrp = find_vpid(pgrp_nr);
 168         do_each_pid_task(pgrp, PIDTYPE_PGID, g) {
 169                 target = g;
 170                 while_each_thread(g, target) {
 171                         if (!security_capset_check(target, effective,
 172                                                    inheritable, permitted)) {
 173                                 security_capset_set(target, effective,
 174                                                     inheritable, permitted);
 175                                 ret = 0;
 176                         }
 177                         found = 1;
 178                 }
 179         } while_each_pid_task(pgrp, PIDTYPE_PGID, g);
 180
 181         read_unlock(&tasklist_lock);
 182         spin_unlock(&task_capability_lock);
 183
 184         if (!found)
 185                 ret = 0;
 186         return ret;
 187 }
 188
 189 /*
 190  * cap_set_all - set capabilities for all processes other than init
 191  * and self.  We call this holding task_capability_lock and tasklist_lock.
 192  */
 193 static inline int cap_set_all(kernel_cap_t *effective,
 194                               kernel_cap_t *inheritable,
 195                               kernel_cap_t *permitted)
 196 {
 197         struct task_struct *g, *target;
 198         int ret = -EPERM;
 199         int found = 0;
 200
 201         spin_lock(&task_capability_lock);
 202         read_lock(&tasklist_lock);
 203
 204         do_each_thread(g, target) {
 205                 if (target == current
 206                     || is_container_init(target->group_leader))
 207                         continue;
 208                 found = 1;
 209                 if (security_capset_check(target, effective, inheritable,
 210                                           permitted))
 211                         continue;
 212                 ret = 0;
 213                 security_capset_set(target, effective, inheritable, permitted);
 214         } while_each_thread(g, target);
 215
 216         read_unlock(&tasklist_lock);
 217         spin_unlock(&task_capability_lock);
 218
 219         if (!found)
 220                 ret = 0;
 221
 222         return ret;
 223 }
 224
 225 /*
 226  * Given the target pid does not refer to the current process we
 227  * need more elaborate support... (This support is not present when
 228  * filesystem capabilities are configured.)
 229  */
 230 static inline int do_sys_capset_other_tasks(pid_t pid, kernel_cap_t *effective,
 231                                             kernel_cap_t *inheritable,
 232                                             kernel_cap_t *permitted)
 233 {
 234         struct task_struct *target;
 235         int ret;
 236
 237         if (!capable(CAP_SETPCAP))
 238                 return -EPERM;
 239
 240         if (pid == -1)            /* all procs other than current and init */
 241                 return cap_set_all(effective, inheritable, permitted);
 242
 243         else if (pid < 0)                    /* all procs in process group */
 244                 return cap_set_pg(-pid, effective, inheritable, permitted);
 245
 246         /* target != current */
 247         spin_lock(&task_capability_lock);
 248         read_lock(&tasklist_lock);
 249
 250         target = find_task_by_vpid(pid);
 251         if (!target)
 252                 ret = -ESRCH;
 253         else {
 254                 ret = security_capset_check(target, effective, inheritable,
 255                                             permitted);
 256
 257                 /* having verified that the proposed changes are legal,
 258                    we now put them into effect. */
 259                 if (!ret)
 260                         security_capset_set(target, effective, inheritable,
 261                                             permitted);
 262         }
 263
 264         read_unlock(&tasklist_lock);
 265         spin_unlock(&task_capability_lock);
 266
 267         return ret;
 268 }
 269
 270 #else /* ie., def CONFIG_SECURITY_FILE_CAPABILITIES */
 271
 272 /*
 273  * If we have configured with filesystem capability support, then the
 274  * only thing that can change the capabilities of the current process
 275  * is the current process. As such, we can't be in this code at the
 276  * same time as we are in the process of setting capabilities in this
 277  * process. The net result is that we can limit our use of locks to
 278  * when we are reading the caps of another process.
 279  */
 280 static inline int cap_get_target_pid(pid_t pid, kernel_cap_t *pEp,
 281                                      kernel_cap_t *pIp, kernel_cap_t *pPp)
 282 {
 283         int ret;
 284
 285         if (pid && (pid != task_pid_vnr(current))) {
 286                 struct task_struct *target;
 287
 288                 spin_lock(&task_capability_lock);
 289                 read_lock(&tasklist_lock);
 290
 291                 target = find_task_by_vpid(pid);
 292                 if (!target)
 293                         ret = -ESRCH;
 294                 else
 295                         ret = security_capget(target, pEp, pIp, pPp);
 296
 297                 read_unlock(&tasklist_lock);
 298                 spin_unlock(&task_capability_lock);
 299         } else
 300                 ret = security_capget(current, pEp, pIp, pPp);
 301
 302         return ret;
 303 }
 304
 305 /*
 306  * With filesystem capability support configured, the kernel does not
 307  * permit the changing of capabilities in one process by another
 308  * process. (CAP_SETPCAP has much less broad semantics when configured
 309  * this way.)
 310  */
 311 static inline int do_sys_capset_other_tasks(pid_t pid,
 312                                             kernel_cap_t *effective,
 313                                             kernel_cap_t *inheritable,
 314                                             kernel_cap_t *permitted)
 315 {
 316         return -EPERM;
 317 }
 318
 319 #endif /* ie., ndef CONFIG_SECURITY_FILE_CAPABILITIES */
 320
 321 /*
 322  * Atomically modify the effective capabilities returning the original
 323  * value. No permission check is performed here - it is assumed that the
 324  * caller is permitted to set the desired effective capabilities.
 325  */
 326 kernel_cap_t cap_set_effective(const kernel_cap_t pE_new)
 327 {
 328         kernel_cap_t pE_old;
 329
 330         spin_lock(&task_capability_lock);
 331
 332         pE_old = current->cap_effective;
 333         current->cap_effective = pE_new;
 334
 335         spin_unlock(&task_capability_lock);
 336
 337         return pE_old;
 338 }
 339
 340 EXPORT_SYMBOL(cap_set_effective);
 341
 342 /**
 343  * sys_capget - get the capabilities of a given process.
 344  * @header: pointer to struct that contains capability version and
 345  *      target pid data
 346  * @dataptr: pointer to struct that contains the effective, permitted,
 347  *      and inheritable capabilities that are returned
 348  *
 349  * Returns 0 on success and < 0 on error.
 350  */
 351 asmlinkage long sys_capget(cap_user_header_t header, cap_user_data_t dataptr)
 352 {
 353         int ret = 0;
 354         pid_t pid;
 355         unsigned tocopy;
 356         kernel_cap_t pE, pI, pP;
 357
 358         ret = cap_validate_magic(header, &tocopy);
 359         if (ret != 0)
 360                 return ret;
 361
 362         if (get_user(pid, &header->pid))
 363                 return -EFAULT;
 364
 365         if (pid < 0)
 366                 return -EINVAL;
 367
 368         ret = cap_get_target_pid(pid, &pE, &pI, &pP);
 369
 370         if (!ret) {
 371                 struct __user_cap_data_struct kdata[_KERNEL_CAPABILITY_U32S];
 372                 unsigned i;
 373
 374                 for (i = 0; i < tocopy; i++) {
 375                         kdata[i].effective = pE.cap[i];
 376                         kdata[i].permitted = pP.cap[i];
 377                         kdata[i].inheritable = pI.cap[i];
 378                 }
 379
 380                 /*
 381                  * Note, in the case, tocopy < _KERNEL_CAPABILITY_U32S,
 382                  * we silently drop the upper capabilities here. This
 383                  * has the effect of making older libcap
 384                  * implementations implicitly drop upper capability
 385                  * bits when they perform a: capget/modify/capset
 386                  * sequence.
 387                  *
 388                  * This behavior is considered fail-safe
 389                  * behavior. Upgrading the application to a newer
 390                  * version of libcap will enable access to the newer
 391                  * capabilities.
 392                  *
 393                  * An alternative would be to return an error here
 394                  * (-ERANGE), but that causes legacy applications to
 395                  * unexpectidly fail; the capget/modify/capset aborts
 396                  * before modification is attempted and the application
 397                  * fails.
 398                  */
 399                 if (copy_to_user(dataptr, kdata, tocopy
 400                                  * sizeof(struct __user_cap_data_struct))) {
 401                         return -EFAULT;
 402                 }
 403         }
 404
 405         return ret;
 406 }
 407
 408 /**
 409  * sys_capset - set capabilities for a process or (*) a group of processes
 410  * @header: pointer to struct that contains capability version and
 411  *      target pid data
 412  * @data: pointer to struct that contains the effective, permitted,
 413  *      and inheritable capabilities
 414  *
 415  * Set capabilities for a given process, all processes, or all
 416  * processes in a given process group.
 417  *
 418  * The restrictions on setting capabilities are specified as:
 419  *
 420  * [pid is for the 'target' task.  'current' is the calling task.]
 421  *
 422  * I: any raised capabilities must be a subset of the (old current) permitted
 423  * P: any raised capabilities must be a subset of the (old current) permitted
 424  * E: must be set to a subset of (new target) permitted
 425  *
 426  * Returns 0 on success and < 0 on error.
 427  */
 428 asmlinkage long sys_capset(cap_user_header_t header, const cap_user_data_t data)
 429 {
 430         struct __user_cap_data_struct kdata[_KERNEL_CAPABILITY_U32S];
 431         unsigned i, tocopy;
 432         kernel_cap_t inheritable, permitted, effective;
 433         int ret;
 434         pid_t pid;
 435
 436         ret = cap_validate_magic(header, &tocopy);
 437         if (ret != 0)
 438                 return ret;
 439
 440         if (get_user(pid, &header->pid))
 441                 return -EFAULT;
 442
 443         if (copy_from_user(&kdata, data, tocopy
 444                            * sizeof(struct __user_cap_data_struct))) {
 445                 return -EFAULT;
 446         }
 447
 448         for (i = 0; i < tocopy; i++) {
 449                 effective.cap[i] = kdata[i].effective;
 450                 permitted.cap[i] = kdata[i].permitted;
 451                 inheritable.cap[i] = kdata[i].inheritable;
 452         }
 453         while (i < _KERNEL_CAPABILITY_U32S) {
 454                 effective.cap[i] = 0;
 455                 permitted.cap[i] = 0;
 456                 inheritable.cap[i] = 0;
 457                 i++;
 458         }
 459
 460         if (pid && (pid != task_pid_vnr(current)))
 461                 ret = do_sys_capset_other_tasks(pid, &effective, &inheritable,
 462                                                 &permitted);
 463         else {
 464                 /*
 465                  * This lock is required even when filesystem
 466                  * capability support is configured - it protects the
 467                  * sys_capget() call from returning incorrect data in
 468                  * the case that the targeted process is not the
 469                  * current one.
 470                  */
 471                 spin_lock(&task_capability_lock);
 472
 473                 ret = security_capset_check(current, &effective, &inheritable,
 474                                             &permitted);
 475                 /*
 476                  * Having verified that the proposed changes are
 477                  * legal, we now put them into effect.
 478                  */
 479                 if (!ret)
 480                         security_capset_set(current, &effective, &inheritable,
 481                                             &permitted);
 482                 spin_unlock(&task_capability_lock);
 483         }
 484
 485
 486         return ret;
 487 }
 488
 489 int __capable(struct task_struct *t, int cap)
 490 {
 491         if (security_capable(t, cap) == 0) {
 492                 t->flags |= PF_SUPERPRIV;
 493                 return 1;
 494         }
 495         return 0;
 496 }
 497
 498 int capable(int cap)
 499 {
 500         return __capable(current, cap);
 501 }
 502 EXPORT_SYMBOL(capable);