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 #ifdef CONFIG_SECURITY_FILE_CAPABILITIES
  37 int file_caps_enabled = 1;
  38
  39 static int __init file_caps_disable(char *str)
  40 {
  41         file_caps_enabled = 0;
  42         return 1;
  43 }
  44 __setup("no_file_caps", file_caps_disable);
  45 #endif
  46
  47 /*
  48  * More recent versions of libcap are available from:
  49  *
  50  *   http://www.kernel.org/pub/linux/libs/security/linux-privs/
  51  */
  52
  53 static void warn_legacy_capability_use(void)
  54 {
  55         static int warned;
  56         if (!warned) {
  57                 char name[sizeof(current->comm)];
  58
  59                 printk(KERN_INFO "warning: `%s' uses 32-bit capabilities"
  60                        " (legacy support in use)\n",
  61                        get_task_comm(name, current));
  62                 warned = 1;
  63         }
  64 }
  65
  66 /*
  67  * Version 2 capabilities worked fine, but the linux/capability.h file
  68  * that accompanied their introduction encouraged their use without
  69  * the necessary user-space source code changes. As such, we have
  70  * created a version 3 with equivalent functionality to version 2, but
  71  * with a header change to protect legacy source code from using
  72  * version 2 when it wanted to use version 1. If your system has code
  73  * that trips the following warning, it is using version 2 specific
  74  * capabilities and may be doing so insecurely.
  75  *
  76  * The remedy is to either upgrade your version of libcap (to 2.10+,
  77  * if the application is linked against it), or recompile your
  78  * application with modern kernel headers and this warning will go
  79  * away.
  80  */
  81
  82 static void warn_deprecated_v2(void)
  83 {
  84         static int warned;
  85
  86         if (!warned) {
  87                 char name[sizeof(current->comm)];
  88
  89                 printk(KERN_INFO "warning: `%s' uses deprecated v2"
  90                        " capabilities in a way that may be insecure.\n",
  91                        get_task_comm(name, current));
  92                 warned = 1;
  93         }
  94 }
  95
  96 /*
  97  * Version check. Return the number of u32s in each capability flag
  98  * array, or a negative value on error.
  99  */
 100 static int cap_validate_magic(cap_user_header_t header, unsigned *tocopy)
 101 {
 102         __u32 version;
 103
 104         if (get_user(version, &header->version))
 105                 return -EFAULT;
 106
 107         switch (version) {
 108         case _LINUX_CAPABILITY_VERSION_1:
 109                 warn_legacy_capability_use();
 110                 *tocopy = _LINUX_CAPABILITY_U32S_1;
 111                 break;
 112         case _LINUX_CAPABILITY_VERSION_2:
 113                 warn_deprecated_v2();
 114                 /*
 115                  * fall through - v3 is otherwise equivalent to v2.
 116                  */
 117         case _LINUX_CAPABILITY_VERSION_3:
 118                 *tocopy = _LINUX_CAPABILITY_U32S_3;
 119                 break;
 120         default:
 121                 if (put_user((u32)_KERNEL_CAPABILITY_VERSION, &header->version))
 122                         return -EFAULT;
 123                 return -EINVAL;
 124         }
 125
 126         return 0;
 127 }
 128
 129 #ifndef CONFIG_SECURITY_FILE_CAPABILITIES
 130
 131 /*
 132  * Without filesystem capability support, we nominally support one process
 133  * setting the capabilities of another
 134  */
 135 static inline int cap_get_target_pid(pid_t pid, kernel_cap_t *pEp,
 136                                      kernel_cap_t *pIp, kernel_cap_t *pPp)
 137 {
 138         struct task_struct *target;
 139         int ret;
 140
 141         spin_lock(&task_capability_lock);
 142         read_lock(&tasklist_lock);
 143
 144         if (pid && pid != task_pid_vnr(current)) {
 145                 target = find_task_by_vpid(pid);
 146                 if (!target) {
 147                         ret = -ESRCH;
 148                         goto out;
 149                 }
 150         } else
 151                 target = current;
 152
 153         ret = security_capget(target, pEp, pIp, pPp);
 154
 155 out:
 156         read_unlock(&tasklist_lock);
 157         spin_unlock(&task_capability_lock);
 158
 159         return ret;
 160 }
 161
 162 /*
 163  * cap_set_pg - set capabilities for all processes in a given process
 164  * group.  We call this holding task_capability_lock and tasklist_lock.
 165  */
 166 static inline int cap_set_pg(int pgrp_nr, kernel_cap_t *effective,
 167                              kernel_cap_t *inheritable,
 168                              kernel_cap_t *permitted)
 169 {
 170         struct task_struct *g, *target;
 171         int ret = -EPERM;
 172         int found = 0;
 173         struct pid *pgrp;
 174
 175         spin_lock(&task_capability_lock);
 176         read_lock(&tasklist_lock);
 177
 178         pgrp = find_vpid(pgrp_nr);
 179         do_each_pid_task(pgrp, PIDTYPE_PGID, g) {
 180                 target = g;
 181                 while_each_thread(g, target) {
 182                         if (!security_capset_check(target, effective,
 183                                                    inheritable, permitted)) {
 184                                 security_capset_set(target, effective,
 185                                                     inheritable, permitted);
 186                                 ret = 0;
 187                         }
 188                         found = 1;
 189                 }
 190         } while_each_pid_task(pgrp, PIDTYPE_PGID, g);
 191
 192         read_unlock(&tasklist_lock);
 193         spin_unlock(&task_capability_lock);
 194
 195         if (!found)
 196                 ret = 0;
 197         return ret;
 198 }
 199
 200 /*
 201  * cap_set_all - set capabilities for all processes other than init
 202  * and self.  We call this holding task_capability_lock and tasklist_lock.
 203  */
 204 static inline int cap_set_all(kernel_cap_t *effective,
 205                               kernel_cap_t *inheritable,
 206                               kernel_cap_t *permitted)
 207 {
 208         struct task_struct *g, *target;
 209         int ret = -EPERM;
 210         int found = 0;
 211
 212         spin_lock(&task_capability_lock);
 213         read_lock(&tasklist_lock);
 214
 215         do_each_thread(g, target) {
 216                 if (target == current
 217                     || is_container_init(target->group_leader))
 218                         continue;
 219                 found = 1;
 220                 if (security_capset_check(target, effective, inheritable,
 221                                           permitted))
 222                         continue;
 223                 ret = 0;
 224                 security_capset_set(target, effective, inheritable, permitted);
 225         } while_each_thread(g, target);
 226
 227         read_unlock(&tasklist_lock);
 228         spin_unlock(&task_capability_lock);
 229
 230         if (!found)
 231                 ret = 0;
 232
 233         return ret;
 234 }
 235
 236 /*
 237  * Given the target pid does not refer to the current process we
 238  * need more elaborate support... (This support is not present when
 239  * filesystem capabilities are configured.)
 240  */
 241 static inline int do_sys_capset_other_tasks(pid_t pid, kernel_cap_t *effective,
 242                                             kernel_cap_t *inheritable,
 243                                             kernel_cap_t *permitted)
 244 {
 245         struct task_struct *target;
 246         int ret;
 247
 248         if (!capable(CAP_SETPCAP))
 249                 return -EPERM;
 250
 251         if (pid == -1)            /* all procs other than current and init */
 252                 return cap_set_all(effective, inheritable, permitted);
 253
 254         else if (pid < 0)                    /* all procs in process group */
 255                 return cap_set_pg(-pid, effective, inheritable, permitted);
 256
 257         /* target != current */
 258         spin_lock(&task_capability_lock);
 259         read_lock(&tasklist_lock);
 260
 261         target = find_task_by_vpid(pid);
 262         if (!target)
 263                 ret = -ESRCH;
 264         else {
 265                 ret = security_capset_check(target, effective, inheritable,
 266                                             permitted);
 267
 268                 /* having verified that the proposed changes are legal,
 269                    we now put them into effect. */
 270                 if (!ret)
 271                         security_capset_set(target, effective, inheritable,
 272                                             permitted);
 273         }
 274
 275         read_unlock(&tasklist_lock);
 276         spin_unlock(&task_capability_lock);
 277
 278         return ret;
 279 }
 280
 281 #else /* ie., def CONFIG_SECURITY_FILE_CAPABILITIES */
 282
 283 /*
 284  * If we have configured with filesystem capability support, then the
 285  * only thing that can change the capabilities of the current process
 286  * is the current process. As such, we can't be in this code at the
 287  * same time as we are in the process of setting capabilities in this
 288  * process. The net result is that we can limit our use of locks to
 289  * when we are reading the caps of another process.
 290  */
 291 static inline int cap_get_target_pid(pid_t pid, kernel_cap_t *pEp,
 292                                      kernel_cap_t *pIp, kernel_cap_t *pPp)
 293 {
 294         int ret;
 295
 296         if (pid && (pid != task_pid_vnr(current))) {
 297                 struct task_struct *target;
 298
 299                 spin_lock(&task_capability_lock);
 300                 read_lock(&tasklist_lock);
 301
 302                 target = find_task_by_vpid(pid);
 303                 if (!target)
 304                         ret = -ESRCH;
 305                 else
 306                         ret = security_capget(target, pEp, pIp, pPp);
 307
 308                 read_unlock(&tasklist_lock);
 309                 spin_unlock(&task_capability_lock);
 310         } else
 311                 ret = security_capget(current, pEp, pIp, pPp);
 312
 313         return ret;
 314 }
 315
 316 /*
 317  * With filesystem capability support configured, the kernel does not
 318  * permit the changing of capabilities in one process by another
 319  * process. (CAP_SETPCAP has much less broad semantics when configured
 320  * this way.)
 321  */
 322 static inline int do_sys_capset_other_tasks(pid_t pid,
 323                                             kernel_cap_t *effective,
 324                                             kernel_cap_t *inheritable,
 325                                             kernel_cap_t *permitted)
 326 {
 327         return -EPERM;
 328 }
 329
 330 #endif /* ie., ndef CONFIG_SECURITY_FILE_CAPABILITIES */
 331
 332 /*
 333  * Atomically modify the effective capabilities returning the original
 334  * value. No permission check is performed here - it is assumed that the
 335  * caller is permitted to set the desired effective capabilities.
 336  */
 337 kernel_cap_t cap_set_effective(const kernel_cap_t pE_new)
 338 {
 339         kernel_cap_t pE_old;
 340
 341         spin_lock(&task_capability_lock);
 342
 343         pE_old = current->cap_effective;
 344         current->cap_effective = pE_new;
 345
 346         spin_unlock(&task_capability_lock);
 347
 348         return pE_old;
 349 }
 350
 351 EXPORT_SYMBOL(cap_set_effective);
 352
 353 /**
 354  * sys_capget - get the capabilities of a given process.
 355  * @header: pointer to struct that contains capability version and
 356  *      target pid data
 357  * @dataptr: pointer to struct that contains the effective, permitted,
 358  *      and inheritable capabilities that are returned
 359  *
 360  * Returns 0 on success and < 0 on error.
 361  */
 362 asmlinkage long sys_capget(cap_user_header_t header, cap_user_data_t dataptr)
 363 {
 364         int ret = 0;
 365         pid_t pid;
 366         unsigned tocopy;
 367         kernel_cap_t pE, pI, pP;
 368
 369         ret = cap_validate_magic(header, &tocopy);
 370         if (ret != 0)
 371                 return ret;
 372
 373         if (get_user(pid, &header->pid))
 374                 return -EFAULT;
 375
 376         if (pid < 0)
 377                 return -EINVAL;
 378
 379         ret = cap_get_target_pid(pid, &pE, &pI, &pP);
 380
 381         if (!ret) {
 382                 struct __user_cap_data_struct kdata[_KERNEL_CAPABILITY_U32S];
 383                 unsigned i;
 384
 385                 for (i = 0; i < tocopy; i++) {
 386                         kdata[i].effective = pE.cap[i];
 387                         kdata[i].permitted = pP.cap[i];
 388                         kdata[i].inheritable = pI.cap[i];
 389                 }
 390
 391                 /*
 392                  * Note, in the case, tocopy < _KERNEL_CAPABILITY_U32S,
 393                  * we silently drop the upper capabilities here. This
 394                  * has the effect of making older libcap
 395                  * implementations implicitly drop upper capability
 396                  * bits when they perform a: capget/modify/capset
 397                  * sequence.
 398                  *
 399                  * This behavior is considered fail-safe
 400                  * behavior. Upgrading the application to a newer
 401                  * version of libcap will enable access to the newer
 402                  * capabilities.
 403                  *
 404                  * An alternative would be to return an error here
 405                  * (-ERANGE), but that causes legacy applications to
 406                  * unexpectidly fail; the capget/modify/capset aborts
 407                  * before modification is attempted and the application
 408                  * fails.
 409                  */
 410                 if (copy_to_user(dataptr, kdata, tocopy
 411                                  * sizeof(struct __user_cap_data_struct))) {
 412                         return -EFAULT;
 413                 }
 414         }
 415
 416         return ret;
 417 }
 418
 419 /**
 420  * sys_capset - set capabilities for a process or (*) a group of processes
 421  * @header: pointer to struct that contains capability version and
 422  *      target pid data
 423  * @data: pointer to struct that contains the effective, permitted,
 424  *      and inheritable capabilities
 425  *
 426  * Set capabilities for a given process, all processes, or all
 427  * processes in a given process group.
 428  *
 429  * The restrictions on setting capabilities are specified as:
 430  *
 431  * [pid is for the 'target' task.  'current' is the calling task.]
 432  *
 433  * I: any raised capabilities must be a subset of the (old current) permitted
 434  * P: any raised capabilities must be a subset of the (old current) permitted
 435  * E: must be set to a subset of (new target) permitted
 436  *
 437  * Returns 0 on success and < 0 on error.
 438  */
 439 asmlinkage long sys_capset(cap_user_header_t header, const cap_user_data_t data)
 440 {
 441         struct __user_cap_data_struct kdata[_KERNEL_CAPABILITY_U32S];
 442         unsigned i, tocopy;
 443         kernel_cap_t inheritable, permitted, effective;
 444         int ret;
 445         pid_t pid;
 446
 447         ret = cap_validate_magic(header, &tocopy);
 448         if (ret != 0)
 449                 return ret;
 450
 451         if (get_user(pid, &header->pid))
 452                 return -EFAULT;
 453
 454         if (copy_from_user(&kdata, data, tocopy
 455                            * sizeof(struct __user_cap_data_struct))) {
 456                 return -EFAULT;
 457         }
 458
 459         for (i = 0; i < tocopy; i++) {
 460                 effective.cap[i] = kdata[i].effective;
 461                 permitted.cap[i] = kdata[i].permitted;
 462                 inheritable.cap[i] = kdata[i].inheritable;
 463         }
 464         while (i < _KERNEL_CAPABILITY_U32S) {
 465                 effective.cap[i] = 0;
 466                 permitted.cap[i] = 0;
 467                 inheritable.cap[i] = 0;
 468                 i++;
 469         }
 470
 471         if (pid && (pid != task_pid_vnr(current)))
 472                 ret = do_sys_capset_other_tasks(pid, &effective, &inheritable,
 473                                                 &permitted);
 474         else {
 475                 /*
 476                  * This lock is required even when filesystem
 477                  * capability support is configured - it protects the
 478                  * sys_capget() call from returning incorrect data in
 479                  * the case that the targeted process is not the
 480                  * current one.
 481                  */
 482                 spin_lock(&task_capability_lock);
 483
 484                 ret = security_capset_check(current, &effective, &inheritable,
 485                                             &permitted);
 486                 /*
 487                  * Having verified that the proposed changes are
 488                  * legal, we now put them into effect.
 489                  */
 490                 if (!ret)
 491                         security_capset_set(current, &effective, &inheritable,
 492                                             &permitted);
 493                 spin_unlock(&task_capability_lock);
 494         }
 495
 496
 497         return ret;
 498 }
 499
 500 /**
 501  * capable - Determine if the current task has a superior capability in effect
 502  * @cap: The capability to be tested for
 503  *
 504  * Return true if the current task has the given superior capability currently
 505  * available for use, false if not.
 506  *
 507  * This sets PF_SUPERPRIV on the task if the capability is available on the
 508  * assumption that it's about to be used.
 509  */
 510 int capable(int cap)
 511 {
 512         if (has_capability(current, cap)) {
 513                 current->flags |= PF_SUPERPRIV;
 514                 return 1;
 515         }
 516         return 0;
 517 }
 518 EXPORT_SYMBOL(capable);