linux/kernel/capability.c
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   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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  11
  12#include <linux/audit.h>
  13#include <linux/capability.h>
  14#include <linux/mm.h>
  15#include <linux/export.h>
  16#include <linux/security.h>
  17#include <linux/syscalls.h>
  18#include <linux/pid_namespace.h>
  19#include <linux/user_namespace.h>
  20#include <asm/uaccess.h>
  21
  22/*
  23 * Leveraged for setting/resetting capabilities
  24 */
  25
  26const kernel_cap_t __cap_empty_set = CAP_EMPTY_SET;
  27EXPORT_SYMBOL(__cap_empty_set);
  28
  29int file_caps_enabled = 1;
  30
  31static int __init file_caps_disable(char *str)
  32{
  33        file_caps_enabled = 0;
  34        return 1;
  35}
  36__setup("no_file_caps", file_caps_disable);
  37
  38#ifdef CONFIG_MULTIUSER
  39/*
  40 * More recent versions of libcap are available from:
  41 *
  42 *   http://www.kernel.org/pub/linux/libs/security/linux-privs/
  43 */
  44
  45static void warn_legacy_capability_use(void)
  46{
  47        char name[sizeof(current->comm)];
  48
  49        pr_info_once("warning: `%s' uses 32-bit capabilities (legacy support in use)\n",
  50                     get_task_comm(name, current));
  51}
  52
  53/*
  54 * Version 2 capabilities worked fine, but the linux/capability.h file
  55 * that accompanied their introduction encouraged their use without
  56 * the necessary user-space source code changes. As such, we have
  57 * created a version 3 with equivalent functionality to version 2, but
  58 * with a header change to protect legacy source code from using
  59 * version 2 when it wanted to use version 1. If your system has code
  60 * that trips the following warning, it is using version 2 specific
  61 * capabilities and may be doing so insecurely.
  62 *
  63 * The remedy is to either upgrade your version of libcap (to 2.10+,
  64 * if the application is linked against it), or recompile your
  65 * application with modern kernel headers and this warning will go
  66 * away.
  67 */
  68
  69static void warn_deprecated_v2(void)
  70{
  71        char name[sizeof(current->comm)];
  72
  73        pr_info_once("warning: `%s' uses deprecated v2 capabilities in a way that may be insecure\n",
  74                     get_task_comm(name, current));
  75}
  76
  77/*
  78 * Version check. Return the number of u32s in each capability flag
  79 * array, or a negative value on error.
  80 */
  81static int cap_validate_magic(cap_user_header_t header, unsigned *tocopy)
  82{
  83        __u32 version;
  84
  85        if (get_user(version, &header->version))
  86                return -EFAULT;
  87
  88        switch (version) {
  89        case _LINUX_CAPABILITY_VERSION_1:
  90                warn_legacy_capability_use();
  91                *tocopy = _LINUX_CAPABILITY_U32S_1;
  92                break;
  93        case _LINUX_CAPABILITY_VERSION_2:
  94                warn_deprecated_v2();
  95                /*
  96                 * fall through - v3 is otherwise equivalent to v2.
  97                 */
  98        case _LINUX_CAPABILITY_VERSION_3:
  99                *tocopy = _LINUX_CAPABILITY_U32S_3;
 100                break;
 101        default:
 102                if (put_user((u32)_KERNEL_CAPABILITY_VERSION, &header->version))
 103                        return -EFAULT;
 104                return -EINVAL;
 105        }
 106
 107        return 0;
 108}
 109
 110/*
 111 * The only thing that can change the capabilities of the current
 112 * process is the current process. As such, we can't be in this code
 113 * at the same time as we are in the process of setting capabilities
 114 * in this process. The net result is that we can limit our use of
 115 * locks to when we are reading the caps of another process.
 116 */
 117static inline int cap_get_target_pid(pid_t pid, kernel_cap_t *pEp,
 118                                     kernel_cap_t *pIp, kernel_cap_t *pPp)
 119{
 120        int ret;
 121
 122        if (pid && (pid != task_pid_vnr(current))) {
 123                struct task_struct *target;
 124
 125                rcu_read_lock();
 126
 127                target = find_task_by_vpid(pid);
 128                if (!target)
 129                        ret = -ESRCH;
 130                else
 131                        ret = security_capget(target, pEp, pIp, pPp);
 132
 133                rcu_read_unlock();
 134        } else
 135                ret = security_capget(current, pEp, pIp, pPp);
 136
 137        return ret;
 138}
 139
 140/**
 141 * sys_capget - get the capabilities of a given process.
 142 * @header: pointer to struct that contains capability version and
 143 *      target pid data
 144 * @dataptr: pointer to struct that contains the effective, permitted,
 145 *      and inheritable capabilities that are returned
 146 *
 147 * Returns 0 on success and < 0 on error.
 148 */
 149SYSCALL_DEFINE2(capget, cap_user_header_t, header, cap_user_data_t, dataptr)
 150{
 151        int ret = 0;
 152        pid_t pid;
 153        unsigned tocopy;
 154        kernel_cap_t pE, pI, pP;
 155
 156        ret = cap_validate_magic(header, &tocopy);
 157        if ((dataptr == NULL) || (ret != 0))
 158                return ((dataptr == NULL) && (ret == -EINVAL)) ? 0 : ret;
 159
 160        if (get_user(pid, &header->pid))
 161                return -EFAULT;
 162
 163        if (pid < 0)
 164                return -EINVAL;
 165
 166        ret = cap_get_target_pid(pid, &pE, &pI, &pP);
 167        if (!ret) {
 168                struct __user_cap_data_struct kdata[_KERNEL_CAPABILITY_U32S];
 169                unsigned i;
 170
 171                for (i = 0; i < tocopy; i++) {
 172                        kdata[i].effective = pE.cap[i];
 173                        kdata[i].permitted = pP.cap[i];
 174                        kdata[i].inheritable = pI.cap[i];
 175                }
 176
 177                /*
 178                 * Note, in the case, tocopy < _KERNEL_CAPABILITY_U32S,
 179                 * we silently drop the upper capabilities here. This
 180                 * has the effect of making older libcap
 181                 * implementations implicitly drop upper capability
 182                 * bits when they perform a: capget/modify/capset
 183                 * sequence.
 184                 *
 185                 * This behavior is considered fail-safe
 186                 * behavior. Upgrading the application to a newer
 187                 * version of libcap will enable access to the newer
 188                 * capabilities.
 189                 *
 190                 * An alternative would be to return an error here
 191                 * (-ERANGE), but that causes legacy applications to
 192                 * unexpectedly fail; the capget/modify/capset aborts
 193                 * before modification is attempted and the application
 194                 * fails.
 195                 */
 196                if (copy_to_user(dataptr, kdata, tocopy
 197                                 * sizeof(struct __user_cap_data_struct))) {
 198                        return -EFAULT;
 199                }
 200        }
 201
 202        return ret;
 203}
 204
 205/**
 206 * sys_capset - set capabilities for a process or (*) a group of processes
 207 * @header: pointer to struct that contains capability version and
 208 *      target pid data
 209 * @data: pointer to struct that contains the effective, permitted,
 210 *      and inheritable capabilities
 211 *
 212 * Set capabilities for the current process only.  The ability to any other
 213 * process(es) has been deprecated and removed.
 214 *
 215 * The restrictions on setting capabilities are specified as:
 216 *
 217 * I: any raised capabilities must be a subset of the old permitted
 218 * P: any raised capabilities must be a subset of the old permitted
 219 * E: must be set to a subset of new permitted
 220 *
 221 * Returns 0 on success and < 0 on error.
 222 */
 223SYSCALL_DEFINE2(capset, cap_user_header_t, header, const cap_user_data_t, data)
 224{
 225        struct __user_cap_data_struct kdata[_KERNEL_CAPABILITY_U32S];
 226        unsigned i, tocopy, copybytes;
 227        kernel_cap_t inheritable, permitted, effective;
 228        struct cred *new;
 229        int ret;
 230        pid_t pid;
 231
 232        ret = cap_validate_magic(header, &tocopy);
 233        if (ret != 0)
 234                return ret;
 235
 236        if (get_user(pid, &header->pid))
 237                return -EFAULT;
 238
 239        /* may only affect current now */
 240        if (pid != 0 && pid != task_pid_vnr(current))
 241                return -EPERM;
 242
 243        copybytes = tocopy * sizeof(struct __user_cap_data_struct);
 244        if (copybytes > sizeof(kdata))
 245                return -EFAULT;
 246
 247        if (copy_from_user(&kdata, data, copybytes))
 248                return -EFAULT;
 249
 250        for (i = 0; i < tocopy; i++) {
 251                effective.cap[i] = kdata[i].effective;
 252                permitted.cap[i] = kdata[i].permitted;
 253                inheritable.cap[i] = kdata[i].inheritable;
 254        }
 255        while (i < _KERNEL_CAPABILITY_U32S) {
 256                effective.cap[i] = 0;
 257                permitted.cap[i] = 0;
 258                inheritable.cap[i] = 0;
 259                i++;
 260        }
 261
 262        effective.cap[CAP_LAST_U32] &= CAP_LAST_U32_VALID_MASK;
 263        permitted.cap[CAP_LAST_U32] &= CAP_LAST_U32_VALID_MASK;
 264        inheritable.cap[CAP_LAST_U32] &= CAP_LAST_U32_VALID_MASK;
 265
 266        new = prepare_creds();
 267        if (!new)
 268                return -ENOMEM;
 269
 270        ret = security_capset(new, current_cred(),
 271                              &effective, &inheritable, &permitted);
 272        if (ret < 0)
 273                goto error;
 274
 275        audit_log_capset(new, current_cred());
 276
 277        return commit_creds(new);
 278
 279error:
 280        abort_creds(new);
 281        return ret;
 282}
 283
 284/**
 285 * has_ns_capability - Does a task have a capability in a specific user ns
 286 * @t: The task in question
 287 * @ns: target user namespace
 288 * @cap: The capability to be tested for
 289 *
 290 * Return true if the specified task has the given superior capability
 291 * currently in effect to the specified user namespace, false if not.
 292 *
 293 * Note that this does not set PF_SUPERPRIV on the task.
 294 */
 295bool has_ns_capability(struct task_struct *t,
 296                       struct user_namespace *ns, int cap)
 297{
 298        int ret;
 299
 300        rcu_read_lock();
 301        ret = security_capable(__task_cred(t), ns, cap);
 302        rcu_read_unlock();
 303
 304        return (ret == 0);
 305}
 306
 307/**
 308 * has_capability - Does a task have a capability in init_user_ns
 309 * @t: The task in question
 310 * @cap: The capability to be tested for
 311 *
 312 * Return true if the specified task has the given superior capability
 313 * currently in effect to the initial user namespace, false if not.
 314 *
 315 * Note that this does not set PF_SUPERPRIV on the task.
 316 */
 317bool has_capability(struct task_struct *t, int cap)
 318{
 319        return has_ns_capability(t, &init_user_ns, cap);
 320}
 321
 322/**
 323 * has_ns_capability_noaudit - Does a task have a capability (unaudited)
 324 * in a specific user ns.
 325 * @t: The task in question
 326 * @ns: target user namespace
 327 * @cap: The capability to be tested for
 328 *
 329 * Return true if the specified task has the given superior capability
 330 * currently in effect to the specified user namespace, false if not.
 331 * Do not write an audit message for the check.
 332 *
 333 * Note that this does not set PF_SUPERPRIV on the task.
 334 */
 335bool has_ns_capability_noaudit(struct task_struct *t,
 336                               struct user_namespace *ns, int cap)
 337{
 338        int ret;
 339
 340        rcu_read_lock();
 341        ret = security_capable_noaudit(__task_cred(t), ns, cap);
 342        rcu_read_unlock();
 343
 344        return (ret == 0);
 345}
 346
 347/**
 348 * has_capability_noaudit - Does a task have a capability (unaudited) in the
 349 * initial user ns
 350 * @t: The task in question
 351 * @cap: The capability to be tested for
 352 *
 353 * Return true if the specified task has the given superior capability
 354 * currently in effect to init_user_ns, false if not.  Don't write an
 355 * audit message for the check.
 356 *
 357 * Note that this does not set PF_SUPERPRIV on the task.
 358 */
 359bool has_capability_noaudit(struct task_struct *t, int cap)
 360{
 361        return has_ns_capability_noaudit(t, &init_user_ns, cap);
 362}
 363
 364static bool ns_capable_common(struct user_namespace *ns, int cap, bool audit)
 365{
 366        int capable;
 367
 368        if (unlikely(!cap_valid(cap))) {
 369                pr_crit("capable() called with invalid cap=%u\n", cap);
 370                BUG();
 371        }
 372
 373        capable = audit ? security_capable(current_cred(), ns, cap) :
 374                          security_capable_noaudit(current_cred(), ns, cap);
 375        if (capable == 0) {
 376                current->flags |= PF_SUPERPRIV;
 377                return true;
 378        }
 379        return false;
 380}
 381
 382/**
 383 * ns_capable - Determine if the current task has a superior capability in effect
 384 * @ns:  The usernamespace we want the capability in
 385 * @cap: The capability to be tested for
 386 *
 387 * Return true if the current task has the given superior capability currently
 388 * available for use, false if not.
 389 *
 390 * This sets PF_SUPERPRIV on the task if the capability is available on the
 391 * assumption that it's about to be used.
 392 */
 393bool ns_capable(struct user_namespace *ns, int cap)
 394{
 395        return ns_capable_common(ns, cap, true);
 396}
 397EXPORT_SYMBOL(ns_capable);
 398
 399/**
 400 * ns_capable_noaudit - Determine if the current task has a superior capability
 401 * (unaudited) in effect
 402 * @ns:  The usernamespace we want the capability in
 403 * @cap: The capability to be tested for
 404 *
 405 * Return true if the current task has the given superior capability currently
 406 * available for use, false if not.
 407 *
 408 * This sets PF_SUPERPRIV on the task if the capability is available on the
 409 * assumption that it's about to be used.
 410 */
 411bool ns_capable_noaudit(struct user_namespace *ns, int cap)
 412{
 413        return ns_capable_common(ns, cap, false);
 414}
 415EXPORT_SYMBOL(ns_capable_noaudit);
 416
 417/**
 418 * capable - Determine if the current task has a superior capability in effect
 419 * @cap: The capability to be tested for
 420 *
 421 * Return true if the current task has the given superior capability currently
 422 * available for use, false if not.
 423 *
 424 * This sets PF_SUPERPRIV on the task if the capability is available on the
 425 * assumption that it's about to be used.
 426 */
 427bool capable(int cap)
 428{
 429        return ns_capable(&init_user_ns, cap);
 430}
 431EXPORT_SYMBOL(capable);
 432#endif /* CONFIG_MULTIUSER */
 433
 434/**
 435 * file_ns_capable - Determine if the file's opener had a capability in effect
 436 * @file:  The file we want to check
 437 * @ns:  The usernamespace we want the capability in
 438 * @cap: The capability to be tested for
 439 *
 440 * Return true if task that opened the file had a capability in effect
 441 * when the file was opened.
 442 *
 443 * This does not set PF_SUPERPRIV because the caller may not
 444 * actually be privileged.
 445 */
 446bool file_ns_capable(const struct file *file, struct user_namespace *ns,
 447                     int cap)
 448{
 449        if (WARN_ON_ONCE(!cap_valid(cap)))
 450                return false;
 451
 452        if (security_capable(file->f_cred, ns, cap) == 0)
 453                return true;
 454
 455        return false;
 456}
 457EXPORT_SYMBOL(file_ns_capable);
 458
 459/**
 460 * capable_wrt_inode_uidgid - Check nsown_capable and uid and gid mapped
 461 * @inode: The inode in question
 462 * @cap: The capability in question
 463 *
 464 * Return true if the current task has the given capability targeted at
 465 * its own user namespace and that the given inode's uid and gid are
 466 * mapped into the current user namespace.
 467 */
 468bool capable_wrt_inode_uidgid(const struct inode *inode, int cap)
 469{
 470        struct user_namespace *ns = current_user_ns();
 471
 472        return ns_capable(ns, cap) && kuid_has_mapping(ns, inode->i_uid) &&
 473                kgid_has_mapping(ns, inode->i_gid);
 474}
 475EXPORT_SYMBOL(capable_wrt_inode_uidgid);
 476