kernel/capability.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * linux/kernel/capability.c
   4  *
   5  * Copyright (C) 1997  Andrew Main <zefram@fysh.org>
   6  *
   7  * Integrated into 2.1.97+,  Andrew G. Morgan <morgan@kernel.org>
   8  * 30 May 2002: Cleanup, Robert M. Love <rml@tech9.net>
   9  */
  10
  11 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  12
  13 #include <linux/audit.h>
  14 #include <linux/capability.h>
  15 #include <linux/mm.h>
  16 #include <linux/export.h>
  17 #include <linux/security.h>
  18 #include <linux/syscalls.h>
  19 #include <linux/pid_namespace.h>
  20 #include <linux/user_namespace.h>
  21 #include <linux/uaccess.h>
  22
  23 /*
  24  * Leveraged for setting/resetting capabilities
  25  */
  26
  27 const kernel_cap_t __cap_empty_set = CAP_EMPTY_SET;
  28 EXPORT_SYMBOL(__cap_empty_set);
  29
  30 int file_caps_enabled = 1;
  31
  32 static int __init file_caps_disable(char *str)
  33 {
  34         file_caps_enabled = 0;
  35         return 1;
  36 }
  37 __setup("no_file_caps", file_caps_disable);
  38
  39 #ifdef CONFIG_MULTIUSER
  40 /*
  41  * More recent versions of libcap are available from:
  42  *
  43  *   http://www.kernel.org/pub/linux/libs/security/linux-privs/
  44  */
  45
  46 static void warn_legacy_capability_use(void)
  47 {
  48         char name[sizeof(current->comm)];
  49
  50         pr_info_once("warning: `%s' uses 32-bit capabilities (legacy support in use)\n",
  51                      get_task_comm(name, current));
  52 }
  53
  54 /*
  55  * Version 2 capabilities worked fine, but the linux/capability.h file
  56  * that accompanied their introduction encouraged their use without
  57  * the necessary user-space source code changes. As such, we have
  58  * created a version 3 with equivalent functionality to version 2, but
  59  * with a header change to protect legacy source code from using
  60  * version 2 when it wanted to use version 1. If your system has code
  61  * that trips the following warning, it is using version 2 specific
  62  * capabilities and may be doing so insecurely.
  63  *
  64  * The remedy is to either upgrade your version of libcap (to 2.10+,
  65  * if the application is linked against it), or recompile your
  66  * application with modern kernel headers and this warning will go
  67  * away.
  68  */
  69
  70 static void warn_deprecated_v2(void)
  71 {
  72         char name[sizeof(current->comm)];
  73
  74         pr_info_once("warning: `%s' uses deprecated v2 capabilities in a way that may be insecure\n",
  75                      get_task_comm(name, current));
  76 }
  77
  78 /*
  79  * Version check. Return the number of u32s in each capability flag
  80  * array, or a negative value on error.
  81  */
  82 static int cap_validate_magic(cap_user_header_t header, unsigned *tocopy)
  83 {
  84         __u32 version;
  85
  86         if (get_user(version, &header->version))
  87                 return -EFAULT;
  88
  89         switch (version) {
  90         case _LINUX_CAPABILITY_VERSION_1:
  91                 warn_legacy_capability_use();
  92                 *tocopy = _LINUX_CAPABILITY_U32S_1;
  93                 break;
  94         case _LINUX_CAPABILITY_VERSION_2:
  95                 warn_deprecated_v2();
  96                 /* fall through - v3 is otherwise equivalent to v2. */
  97         case _LINUX_CAPABILITY_VERSION_3:
  98                 *tocopy = _LINUX_CAPABILITY_U32S_3;
  99                 break;
 100         default:
 101                 if (put_user((u32)_KERNEL_CAPABILITY_VERSION, &header->version))
 102                         return -EFAULT;
 103                 return -EINVAL;
 104         }
 105
 106         return 0;
 107 }
 108
 109 /*
 110  * The only thing that can change the capabilities of the current
 111  * process is the current process. As such, we can't be in this code
 112  * at the same time as we are in the process of setting capabilities
 113  * in this process. The net result is that we can limit our use of
 114  * locks to when we are reading the caps of another process.
 115  */
 116 static inline int cap_get_target_pid(pid_t pid, kernel_cap_t *pEp,
 117                                      kernel_cap_t *pIp, kernel_cap_t *pPp)
 118 {
 119         int ret;
 120
 121         if (pid && (pid != task_pid_vnr(current))) {
 122                 struct task_struct *target;
 123
 124                 rcu_read_lock();
 125
 126                 target = find_task_by_vpid(pid);
 127                 if (!target)
 128                         ret = -ESRCH;
 129                 else
 130                         ret = security_capget(target, pEp, pIp, pPp);
 131
 132                 rcu_read_unlock();
 133         } else
 134                 ret = security_capget(current, pEp, pIp, pPp);
 135
 136         return ret;
 137 }
 138
 139 /**
 140  * sys_capget - get the capabilities of a given process.
 141  * @header: pointer to struct that contains capability version and
 142  *      target pid data
 143  * @dataptr: pointer to struct that contains the effective, permitted,
 144  *      and inheritable capabilities that are returned
 145  *
 146  * Returns 0 on success and < 0 on error.
 147  */
 148 SYSCALL_DEFINE2(capget, cap_user_header_t, header, cap_user_data_t, dataptr)
 149 {
 150         int ret = 0;
 151         pid_t pid;
 152         unsigned tocopy;
 153         kernel_cap_t pE, pI, pP;
 154
 155         ret = cap_validate_magic(header, &tocopy);
 156         if ((dataptr == NULL) || (ret != 0))
 157                 return ((dataptr == NULL) && (ret == -EINVAL)) ? 0 : ret;
 158
 159         if (get_user(pid, &header->pid))
 160                 return -EFAULT;
 161
 162         if (pid < 0)
 163                 return -EINVAL;
 164
 165         ret = cap_get_target_pid(pid, &pE, &pI, &pP);
 166         if (!ret) {
 167                 struct __user_cap_data_struct kdata[_KERNEL_CAPABILITY_U32S];
 168                 unsigned i;
 169
 170                 for (i = 0; i < tocopy; i++) {
 171                         kdata[i].effective = pE.cap[i];
 172                         kdata[i].permitted = pP.cap[i];
 173                         kdata[i].inheritable = pI.cap[i];
 174                 }
 175
 176                 /*
 177                  * Note, in the case, tocopy < _KERNEL_CAPABILITY_U32S,
 178                  * we silently drop the upper capabilities here. This
 179                  * has the effect of making older libcap
 180                  * implementations implicitly drop upper capability
 181                  * bits when they perform a: capget/modify/capset
 182                  * sequence.
 183                  *
 184                  * This behavior is considered fail-safe
 185                  * behavior. Upgrading the application to a newer
 186                  * version of libcap will enable access to the newer
 187                  * capabilities.
 188                  *
 189                  * An alternative would be to return an error here
 190                  * (-ERANGE), but that causes legacy applications to
 191                  * unexpectedly fail; the capget/modify/capset aborts
 192                  * before modification is attempted and the application
 193                  * fails.
 194                  */
 195                 if (copy_to_user(dataptr, kdata, tocopy
 196                                  * sizeof(struct __user_cap_data_struct))) {
 197                         return -EFAULT;
 198                 }
 199         }
 200
 201         return ret;
 202 }
 203
 204 /**
 205  * sys_capset - set capabilities for a process or (*) a group of processes
 206  * @header: pointer to struct that contains capability version and
 207  *      target pid data
 208  * @data: pointer to struct that contains the effective, permitted,
 209  *      and inheritable capabilities
 210  *
 211  * Set capabilities for the current process only.  The ability to any other
 212  * process(es) has been deprecated and removed.
 213  *
 214  * The restrictions on setting capabilities are specified as:
 215  *
 216  * I: any raised capabilities must be a subset of the old permitted
 217  * P: any raised capabilities must be a subset of the old permitted
 218  * E: must be set to a subset of new permitted
 219  *
 220  * Returns 0 on success and < 0 on error.
 221  */
 222 SYSCALL_DEFINE2(capset, cap_user_header_t, header, const cap_user_data_t, data)
 223 {
 224         struct __user_cap_data_struct kdata[_KERNEL_CAPABILITY_U32S];
 225         unsigned i, tocopy, copybytes;
 226         kernel_cap_t inheritable, permitted, effective;
 227         struct cred *new;
 228         int ret;
 229         pid_t pid;
 230
 231         ret = cap_validate_magic(header, &tocopy);
 232         if (ret != 0)
 233                 return ret;
 234
 235         if (get_user(pid, &header->pid))
 236                 return -EFAULT;
 237
 238         /* may only affect current now */
 239         if (pid != 0 && pid != task_pid_vnr(current))
 240                 return -EPERM;
 241
 242         copybytes = tocopy * sizeof(struct __user_cap_data_struct);
 243         if (copybytes > sizeof(kdata))
 244                 return -EFAULT;
 245
 246         if (copy_from_user(&kdata, data, copybytes))
 247                 return -EFAULT;
 248
 249         for (i = 0; i < tocopy; i++) {
 250                 effective.cap[i] = kdata[i].effective;
 251                 permitted.cap[i] = kdata[i].permitted;
 252                 inheritable.cap[i] = kdata[i].inheritable;
 253         }
 254         while (i < _KERNEL_CAPABILITY_U32S) {
 255                 effective.cap[i] = 0;
 256                 permitted.cap[i] = 0;
 257                 inheritable.cap[i] = 0;
 258                 i++;
 259         }
 260
 261         effective.cap[CAP_LAST_U32] &= CAP_LAST_U32_VALID_MASK;
 262         permitted.cap[CAP_LAST_U32] &= CAP_LAST_U32_VALID_MASK;
 263         inheritable.cap[CAP_LAST_U32] &= CAP_LAST_U32_VALID_MASK;
 264
 265         new = prepare_creds();
 266         if (!new)
 267                 return -ENOMEM;
 268
 269         ret = security_capset(new, current_cred(),
 270                               &effective, &inheritable, &permitted);
 271         if (ret < 0)
 272                 goto error;
 273
 274         audit_log_capset(new, current_cred());
 275
 276         return commit_creds(new);
 277
 278 error:
 279         abort_creds(new);
 280         return ret;
 281 }
 282
 283 /**
 284  * has_ns_capability - Does a task have a capability in a specific user ns
 285  * @t: The task in question
 286  * @ns: target user namespace
 287  * @cap: The capability to be tested for
 288  *
 289  * Return true if the specified task has the given superior capability
 290  * currently in effect to the specified user namespace, false if not.
 291  *
 292  * Note that this does not set PF_SUPERPRIV on the task.
 293  */
 294 bool has_ns_capability(struct task_struct *t,
 295                        struct user_namespace *ns, int cap)
 296 {
 297         int ret;
 298
 299         rcu_read_lock();
 300         ret = security_capable(__task_cred(t), ns, cap, CAP_OPT_NONE);
 301         rcu_read_unlock();
 302
 303         return (ret == 0);
 304 }
 305
 306 /**
 307  * has_capability - Does a task have a capability in init_user_ns
 308  * @t: The task in question
 309  * @cap: The capability to be tested for
 310  *
 311  * Return true if the specified task has the given superior capability
 312  * currently in effect to the initial user namespace, false if not.
 313  *
 314  * Note that this does not set PF_SUPERPRIV on the task.
 315  */
 316 bool has_capability(struct task_struct *t, int cap)
 317 {
 318         return has_ns_capability(t, &init_user_ns, cap);
 319 }
 320 EXPORT_SYMBOL(has_capability);
 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  */
 335 bool 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(__task_cred(t), ns, cap, CAP_OPT_NOAUDIT);
 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  */
 359 bool has_capability_noaudit(struct task_struct *t, int cap)
 360 {
 361         return has_ns_capability_noaudit(t, &init_user_ns, cap);
 362 }
 363
 364 static bool ns_capable_common(struct user_namespace *ns,
 365                               int cap,
 366                               unsigned int opts)
 367 {
 368         int capable;
 369
 370         if (unlikely(!cap_valid(cap))) {
 371                 pr_crit("capable() called with invalid cap=%u\n", cap);
 372                 BUG();
 373         }
 374
 375         capable = security_capable(current_cred(), ns, cap, opts);
 376         if (capable == 0) {
 377                 current->flags |= PF_SUPERPRIV;
 378                 return true;
 379         }
 380         return false;
 381 }
 382
 383 /**
 384  * ns_capable - Determine if the current task has a superior capability in effect
 385  * @ns:  The usernamespace we want the capability in
 386  * @cap: The capability to be tested for
 387  *
 388  * Return true if the current task has the given superior capability currently
 389  * available for use, false if not.
 390  *
 391  * This sets PF_SUPERPRIV on the task if the capability is available on the
 392  * assumption that it's about to be used.
 393  */
 394 bool ns_capable(struct user_namespace *ns, int cap)
 395 {
 396         return ns_capable_common(ns, cap, CAP_OPT_NONE);
 397 }
 398 EXPORT_SYMBOL(ns_capable);
 399
 400 /**
 401  * ns_capable_noaudit - Determine if the current task has a superior capability
 402  * (unaudited) in effect
 403  * @ns:  The usernamespace we want the capability in
 404  * @cap: The capability to be tested for
 405  *
 406  * Return true if the current task has the given superior capability currently
 407  * available for use, false if not.
 408  *
 409  * This sets PF_SUPERPRIV on the task if the capability is available on the
 410  * assumption that it's about to be used.
 411  */
 412 bool ns_capable_noaudit(struct user_namespace *ns, int cap)
 413 {
 414         return ns_capable_common(ns, cap, CAP_OPT_NOAUDIT);
 415 }
 416 EXPORT_SYMBOL(ns_capable_noaudit);
 417
 418 /**
 419  * ns_capable_setid - Determine if the current task has a superior capability
 420  * in effect, while signalling that this check is being done from within a
 421  * setid syscall.
 422  * @ns:  The usernamespace we want the capability in
 423  * @cap: The capability to be tested for
 424  *
 425  * Return true if the current task has the given superior capability currently
 426  * available for use, false if not.
 427  *
 428  * This sets PF_SUPERPRIV on the task if the capability is available on the
 429  * assumption that it's about to be used.
 430  */
 431 bool ns_capable_setid(struct user_namespace *ns, int cap)
 432 {
 433         return ns_capable_common(ns, cap, CAP_OPT_INSETID);
 434 }
 435 EXPORT_SYMBOL(ns_capable_setid);
 436
 437 /**
 438  * capable - Determine if the current task has a superior capability in effect
 439  * @cap: The capability to be tested for
 440  *
 441  * Return true if the current task has the given superior capability currently
 442  * available for use, false if not.
 443  *
 444  * This sets PF_SUPERPRIV on the task if the capability is available on the
 445  * assumption that it's about to be used.
 446  */
 447 bool capable(int cap)
 448 {
 449         return ns_capable(&init_user_ns, cap);
 450 }
 451 EXPORT_SYMBOL(capable);
 452 #endif /* CONFIG_MULTIUSER */
 453
 454 /**
 455  * file_ns_capable - Determine if the file's opener had a capability in effect
 456  * @file:  The file we want to check
 457  * @ns:  The usernamespace we want the capability in
 458  * @cap: The capability to be tested for
 459  *
 460  * Return true if task that opened the file had a capability in effect
 461  * when the file was opened.
 462  *
 463  * This does not set PF_SUPERPRIV because the caller may not
 464  * actually be privileged.
 465  */
 466 bool file_ns_capable(const struct file *file, struct user_namespace *ns,
 467                      int cap)
 468 {
 469
 470         if (WARN_ON_ONCE(!cap_valid(cap)))
 471                 return false;
 472
 473         if (security_capable(file->f_cred, ns, cap, CAP_OPT_NONE) == 0)
 474                 return true;
 475
 476         return false;
 477 }
 478 EXPORT_SYMBOL(file_ns_capable);
 479
 480 /**
 481  * privileged_wrt_inode_uidgid - Do capabilities in the namespace work over the inode?
 482  * @ns: The user namespace in question
 483  * @inode: The inode in question
 484  *
 485  * Return true if the inode uid and gid are within the namespace.
 486  */
 487 bool privileged_wrt_inode_uidgid(struct user_namespace *ns, const struct inode *inode)
 488 {
 489         return kuid_has_mapping(ns, inode->i_uid) &&
 490                 kgid_has_mapping(ns, inode->i_gid);
 491 }
 492
 493 /**
 494  * capable_wrt_inode_uidgid - Check nsown_capable and uid and gid mapped
 495  * @inode: The inode in question
 496  * @cap: The capability in question
 497  *
 498  * Return true if the current task has the given capability targeted at
 499  * its own user namespace and that the given inode's uid and gid are
 500  * mapped into the current user namespace.
 501  */
 502 bool capable_wrt_inode_uidgid(const struct inode *inode, int cap)
 503 {
 504         struct user_namespace *ns = current_user_ns();
 505
 506         return ns_capable(ns, cap) && privileged_wrt_inode_uidgid(ns, inode);
 507 }
 508 EXPORT_SYMBOL(capable_wrt_inode_uidgid);
 509
 510 /**
 511  * ptracer_capable - Determine if the ptracer holds CAP_SYS_PTRACE in the namespace
 512  * @tsk: The task that may be ptraced
 513  * @ns: The user namespace to search for CAP_SYS_PTRACE in
 514  *
 515  * Return true if the task that is ptracing the current task had CAP_SYS_PTRACE
 516  * in the specified user namespace.
 517  */
 518 bool ptracer_capable(struct task_struct *tsk, struct user_namespace *ns)
 519 {
 520         int ret = 0;  /* An absent tracer adds no restrictions */
 521         const struct cred *cred;
 522
 523         rcu_read_lock();
 524         cred = rcu_dereference(tsk->ptracer_cred);
 525         if (cred)
 526                 ret = security_capable(cred, ns, CAP_SYS_PTRACE,
 527                                        CAP_OPT_NOAUDIT);
 528         rcu_read_unlock();
 529         return (ret == 0);
 530 }