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                 /*
  97                  * fall through - v3 is otherwise equivalent to v2.
  98                  */
  99         case _LINUX_CAPABILITY_VERSION_3:
 100                 *tocopy = _LINUX_CAPABILITY_U32S_3;
 101                 break;
 102         default:
 103                 if (put_user((u32)_KERNEL_CAPABILITY_VERSION, &header->version))
 104                         return -EFAULT;
 105                 return -EINVAL;
 106         }
 107
 108         return 0;
 109 }
 110
 111 /*
 112  * The only thing that can change the capabilities of the current
 113  * process is the current process. As such, we can't be in this code
 114  * at the same time as we are in the process of setting capabilities
 115  * in this process. The net result is that we can limit our use of
 116  * locks to when we are reading the caps of another process.
 117  */
 118 static inline int cap_get_target_pid(pid_t pid, kernel_cap_t *pEp,
 119                                      kernel_cap_t *pIp, kernel_cap_t *pPp)
 120 {
 121         int ret;
 122
 123         if (pid && (pid != task_pid_vnr(current))) {
 124                 struct task_struct *target;
 125
 126                 rcu_read_lock();
 127
 128                 target = find_task_by_vpid(pid);
 129                 if (!target)
 130                         ret = -ESRCH;
 131                 else
 132                         ret = security_capget(target, pEp, pIp, pPp);
 133
 134                 rcu_read_unlock();
 135         } else
 136                 ret = security_capget(current, pEp, pIp, pPp);
 137
 138         return ret;
 139 }
 140
 141 /**
 142  * sys_capget - get the capabilities of a given process.
 143  * @header: pointer to struct that contains capability version and
 144  *      target pid data
 145  * @dataptr: pointer to struct that contains the effective, permitted,
 146  *      and inheritable capabilities that are returned
 147  *
 148  * Returns 0 on success and < 0 on error.
 149  */
 150 SYSCALL_DEFINE2(capget, cap_user_header_t, header, cap_user_data_t, dataptr)
 151 {
 152         int ret = 0;
 153         pid_t pid;
 154         unsigned tocopy;
 155         kernel_cap_t pE, pI, pP;
 156
 157         ret = cap_validate_magic(header, &tocopy);
 158         if ((dataptr == NULL) || (ret != 0))
 159                 return ((dataptr == NULL) && (ret == -EINVAL)) ? 0 : ret;
 160
 161         if (get_user(pid, &header->pid))
 162                 return -EFAULT;
 163
 164         if (pid < 0)
 165                 return -EINVAL;
 166
 167         ret = cap_get_target_pid(pid, &pE, &pI, &pP);
 168         if (!ret) {
 169                 struct __user_cap_data_struct kdata[_KERNEL_CAPABILITY_U32S];
 170                 unsigned i;
 171
 172                 for (i = 0; i < tocopy; i++) {
 173                         kdata[i].effective = pE.cap[i];
 174                         kdata[i].permitted = pP.cap[i];
 175                         kdata[i].inheritable = pI.cap[i];
 176                 }
 177
 178                 /*
 179                  * Note, in the case, tocopy < _KERNEL_CAPABILITY_U32S,
 180                  * we silently drop the upper capabilities here. This
 181                  * has the effect of making older libcap
 182                  * implementations implicitly drop upper capability
 183                  * bits when they perform a: capget/modify/capset
 184                  * sequence.
 185                  *
 186                  * This behavior is considered fail-safe
 187                  * behavior. Upgrading the application to a newer
 188                  * version of libcap will enable access to the newer
 189                  * capabilities.
 190                  *
 191                  * An alternative would be to return an error here
 192                  * (-ERANGE), but that causes legacy applications to
 193                  * unexpectedly fail; the capget/modify/capset aborts
 194                  * before modification is attempted and the application
 195                  * fails.
 196                  */
 197                 if (copy_to_user(dataptr, kdata, tocopy
 198                                  * sizeof(struct __user_cap_data_struct))) {
 199                         return -EFAULT;
 200                 }
 201         }
 202
 203         return ret;
 204 }
 205
 206 /**
 207  * sys_capset - set capabilities for a process or (*) a group of processes
 208  * @header: pointer to struct that contains capability version and
 209  *      target pid data
 210  * @data: pointer to struct that contains the effective, permitted,
 211  *      and inheritable capabilities
 212  *
 213  * Set capabilities for the current process only.  The ability to any other
 214  * process(es) has been deprecated and removed.
 215  *
 216  * The restrictions on setting capabilities are specified as:
 217  *
 218  * I: any raised capabilities must be a subset of the old permitted
 219  * P: any raised capabilities must be a subset of the old permitted
 220  * E: must be set to a subset of new permitted
 221  *
 222  * Returns 0 on success and < 0 on error.
 223  */
 224 SYSCALL_DEFINE2(capset, cap_user_header_t, header, const cap_user_data_t, data)
 225 {
 226         struct __user_cap_data_struct kdata[_KERNEL_CAPABILITY_U32S];
 227         unsigned i, tocopy, copybytes;
 228         kernel_cap_t inheritable, permitted, effective;
 229         struct cred *new;
 230         int ret;
 231         pid_t pid;
 232
 233         ret = cap_validate_magic(header, &tocopy);
 234         if (ret != 0)
 235                 return ret;
 236
 237         if (get_user(pid, &header->pid))
 238                 return -EFAULT;
 239
 240         /* may only affect current now */
 241         if (pid != 0 && pid != task_pid_vnr(current))
 242                 return -EPERM;
 243
 244         copybytes = tocopy * sizeof(struct __user_cap_data_struct);
 245         if (copybytes > sizeof(kdata))
 246                 return -EFAULT;
 247
 248         if (copy_from_user(&kdata, data, copybytes))
 249                 return -EFAULT;
 250
 251         for (i = 0; i < tocopy; i++) {
 252                 effective.cap[i] = kdata[i].effective;
 253                 permitted.cap[i] = kdata[i].permitted;
 254                 inheritable.cap[i] = kdata[i].inheritable;
 255         }
 256         while (i < _KERNEL_CAPABILITY_U32S) {
 257                 effective.cap[i] = 0;
 258                 permitted.cap[i] = 0;
 259                 inheritable.cap[i] = 0;
 260                 i++;
 261         }
 262
 263         effective.cap[CAP_LAST_U32] &= CAP_LAST_U32_VALID_MASK;
 264         permitted.cap[CAP_LAST_U32] &= CAP_LAST_U32_VALID_MASK;
 265         inheritable.cap[CAP_LAST_U32] &= CAP_LAST_U32_VALID_MASK;
 266
 267         new = prepare_creds();
 268         if (!new)
 269                 return -ENOMEM;
 270
 271         ret = security_capset(new, current_cred(),
 272                               &effective, &inheritable, &permitted);
 273         if (ret < 0)
 274                 goto error;
 275
 276         audit_log_capset(new, current_cred());
 277
 278         return commit_creds(new);
 279
 280 error:
 281         abort_creds(new);
 282         return ret;
 283 }
 284
 285 /**
 286  * has_ns_capability - Does a task have a capability in a specific user ns
 287  * @t: The task in question
 288  * @ns: target user namespace
 289  * @cap: The capability to be tested for
 290  *
 291  * Return true if the specified task has the given superior capability
 292  * currently in effect to the specified user namespace, false if not.
 293  *
 294  * Note that this does not set PF_SUPERPRIV on the task.
 295  */
 296 bool has_ns_capability(struct task_struct *t,
 297                        struct user_namespace *ns, int cap)
 298 {
 299         int ret;
 300
 301         rcu_read_lock();
 302         ret = security_capable(__task_cred(t), ns, cap);
 303         rcu_read_unlock();
 304
 305         return (ret == 0);
 306 }
 307
 308 /**
 309  * has_capability - Does a task have a capability in init_user_ns
 310  * @t: The task in question
 311  * @cap: The capability to be tested for
 312  *
 313  * Return true if the specified task has the given superior capability
 314  * currently in effect to the initial user namespace, false if not.
 315  *
 316  * Note that this does not set PF_SUPERPRIV on the task.
 317  */
 318 bool has_capability(struct task_struct *t, int cap)
 319 {
 320         return has_ns_capability(t, &init_user_ns, cap);
 321 }
 322 EXPORT_SYMBOL(has_capability);
 323
 324 /**
 325  * has_ns_capability_noaudit - Does a task have a capability (unaudited)
 326  * in a specific user ns.
 327  * @t: The task in question
 328  * @ns: target user namespace
 329  * @cap: The capability to be tested for
 330  *
 331  * Return true if the specified task has the given superior capability
 332  * currently in effect to the specified user namespace, false if not.
 333  * Do not write an audit message for the check.
 334  *
 335  * Note that this does not set PF_SUPERPRIV on the task.
 336  */
 337 bool has_ns_capability_noaudit(struct task_struct *t,
 338                                struct user_namespace *ns, int cap)
 339 {
 340         int ret;
 341
 342         rcu_read_lock();
 343         ret = security_capable_noaudit(__task_cred(t), ns, cap);
 344         rcu_read_unlock();
 345
 346         return (ret == 0);
 347 }
 348
 349 /**
 350  * has_capability_noaudit - Does a task have a capability (unaudited) in the
 351  * initial user ns
 352  * @t: The task in question
 353  * @cap: The capability to be tested for
 354  *
 355  * Return true if the specified task has the given superior capability
 356  * currently in effect to init_user_ns, false if not.  Don't write an
 357  * audit message for the check.
 358  *
 359  * Note that this does not set PF_SUPERPRIV on the task.
 360  */
 361 bool has_capability_noaudit(struct task_struct *t, int cap)
 362 {
 363         return has_ns_capability_noaudit(t, &init_user_ns, cap);
 364 }
 365
 366 static bool ns_capable_common(struct user_namespace *ns, int cap, bool audit)
 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 = audit ? security_capable(current_cred(), ns, cap) :
 376                           security_capable_noaudit(current_cred(), ns, cap);
 377         if (capable == 0) {
 378                 current->flags |= PF_SUPERPRIV;
 379                 return true;
 380         }
 381         return false;
 382 }
 383
 384 /**
 385  * ns_capable - Determine if the current task has a superior capability in effect
 386  * @ns:  The usernamespace we want the capability in
 387  * @cap: The capability to be tested for
 388  *
 389  * Return true if the current task has the given superior capability currently
 390  * available for use, false if not.
 391  *
 392  * This sets PF_SUPERPRIV on the task if the capability is available on the
 393  * assumption that it's about to be used.
 394  */
 395 bool ns_capable(struct user_namespace *ns, int cap)
 396 {
 397         return ns_capable_common(ns, cap, true);
 398 }
 399 EXPORT_SYMBOL(ns_capable);
 400
 401 /**
 402  * ns_capable_noaudit - Determine if the current task has a superior capability
 403  * (unaudited) in effect
 404  * @ns:  The usernamespace we want the capability in
 405  * @cap: The capability to be tested for
 406  *
 407  * Return true if the current task has the given superior capability currently
 408  * available for use, false if not.
 409  *
 410  * This sets PF_SUPERPRIV on the task if the capability is available on the
 411  * assumption that it's about to be used.
 412  */
 413 bool ns_capable_noaudit(struct user_namespace *ns, int cap)
 414 {
 415         return ns_capable_common(ns, cap, false);
 416 }
 417 EXPORT_SYMBOL(ns_capable_noaudit);
 418
 419 /**
 420  * capable - Determine if the current task has a superior capability in effect
 421  * @cap: The capability to be tested for
 422  *
 423  * Return true if the current task has the given superior capability currently
 424  * available for use, false if not.
 425  *
 426  * This sets PF_SUPERPRIV on the task if the capability is available on the
 427  * assumption that it's about to be used.
 428  */
 429 bool capable(int cap)
 430 {
 431         return ns_capable(&init_user_ns, cap);
 432 }
 433 EXPORT_SYMBOL(capable);
 434 #endif /* CONFIG_MULTIUSER */
 435
 436 /**
 437  * file_ns_capable - Determine if the file's opener had a capability in effect
 438  * @file:  The file we want to check
 439  * @ns:  The usernamespace we want the capability in
 440  * @cap: The capability to be tested for
 441  *
 442  * Return true if task that opened the file had a capability in effect
 443  * when the file was opened.
 444  *
 445  * This does not set PF_SUPERPRIV because the caller may not
 446  * actually be privileged.
 447  */
 448 bool file_ns_capable(const struct file *file, struct user_namespace *ns,
 449                      int cap)
 450 {
 451         if (WARN_ON_ONCE(!cap_valid(cap)))
 452                 return false;
 453
 454         if (security_capable(file->f_cred, ns, cap) == 0)
 455                 return true;
 456
 457         return false;
 458 }
 459 EXPORT_SYMBOL(file_ns_capable);
 460
 461 /**
 462  * privileged_wrt_inode_uidgid - Do capabilities in the namespace work over the inode?
 463  * @ns: The user namespace in question
 464  * @inode: The inode in question
 465  *
 466  * Return true if the inode uid and gid are within the namespace.
 467  */
 468 bool privileged_wrt_inode_uidgid(struct user_namespace *ns, const struct inode *inode)
 469 {
 470         return kuid_has_mapping(ns, inode->i_uid) &&
 471                 kgid_has_mapping(ns, inode->i_gid);
 472 }
 473
 474 /**
 475  * capable_wrt_inode_uidgid - Check nsown_capable and uid and gid mapped
 476  * @inode: The inode in question
 477  * @cap: The capability in question
 478  *
 479  * Return true if the current task has the given capability targeted at
 480  * its own user namespace and that the given inode's uid and gid are
 481  * mapped into the current user namespace.
 482  */
 483 bool capable_wrt_inode_uidgid(const struct inode *inode, int cap)
 484 {
 485         struct user_namespace *ns = current_user_ns();
 486
 487         return ns_capable(ns, cap) && privileged_wrt_inode_uidgid(ns, inode);
 488 }
 489 EXPORT_SYMBOL(capable_wrt_inode_uidgid);
 490
 491 /**
 492  * ptracer_capable - Determine if the ptracer holds CAP_SYS_PTRACE in the namespace
 493  * @tsk: The task that may be ptraced
 494  * @ns: The user namespace to search for CAP_SYS_PTRACE in
 495  *
 496  * Return true if the task that is ptracing the current task had CAP_SYS_PTRACE
 497  * in the specified user namespace.
 498  */
 499 bool ptracer_capable(struct task_struct *tsk, struct user_namespace *ns)
 500 {
 501         int ret = 0;  /* An absent tracer adds no restrictions */
 502         const struct cred *cred;
 503         rcu_read_lock();
 504         cred = rcu_dereference(tsk->ptracer_cred);
 505         if (cred)
 506                 ret = security_capable_noaudit(cred, ns, CAP_SYS_PTRACE);
 507         rcu_read_unlock();
 508         return (ret == 0);
 509 }