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 int file_caps_enabled = 1;
  24
  25 static int __init file_caps_disable(char *str)
  26 {
  27         file_caps_enabled = 0;
  28         return 1;
  29 }
  30 __setup("no_file_caps", file_caps_disable);
  31
  32 #ifdef CONFIG_MULTIUSER
  33 /*
  34  * More recent versions of libcap are available from:
  35  *
  36  *   http://www.kernel.org/pub/linux/libs/security/linux-privs/
  37  */
  38
  39 static void warn_legacy_capability_use(void)
  40 {
  41         char name[sizeof(current->comm)];
  42
  43         pr_info_once("warning: `%s' uses 32-bit capabilities (legacy support in use)\n",
  44                      get_task_comm(name, current));
  45 }
  46
  47 /*
  48  * Version 2 capabilities worked fine, but the linux/capability.h file
  49  * that accompanied their introduction encouraged their use without
  50  * the necessary user-space source code changes. As such, we have
  51  * created a version 3 with equivalent functionality to version 2, but
  52  * with a header change to protect legacy source code from using
  53  * version 2 when it wanted to use version 1. If your system has code
  54  * that trips the following warning, it is using version 2 specific
  55  * capabilities and may be doing so insecurely.
  56  *
  57  * The remedy is to either upgrade your version of libcap (to 2.10+,
  58  * if the application is linked against it), or recompile your
  59  * application with modern kernel headers and this warning will go
  60  * away.
  61  */
  62
  63 static void warn_deprecated_v2(void)
  64 {
  65         char name[sizeof(current->comm)];
  66
  67         pr_info_once("warning: `%s' uses deprecated v2 capabilities in a way that may be insecure\n",
  68                      get_task_comm(name, current));
  69 }
  70
  71 /*
  72  * Version check. Return the number of u32s in each capability flag
  73  * array, or a negative value on error.
  74  */
  75 static int cap_validate_magic(cap_user_header_t header, unsigned *tocopy)
  76 {
  77         __u32 version;
  78
  79         if (get_user(version, &header->version))
  80                 return -EFAULT;
  81
  82         switch (version) {
  83         case _LINUX_CAPABILITY_VERSION_1:
  84                 warn_legacy_capability_use();
  85                 *tocopy = _LINUX_CAPABILITY_U32S_1;
  86                 break;
  87         case _LINUX_CAPABILITY_VERSION_2:
  88                 warn_deprecated_v2();
  89                 fallthrough;    /* v3 is otherwise equivalent to v2 */
  90         case _LINUX_CAPABILITY_VERSION_3:
  91                 *tocopy = _LINUX_CAPABILITY_U32S_3;
  92                 break;
  93         default:
  94                 if (put_user((u32)_KERNEL_CAPABILITY_VERSION, &header->version))
  95                         return -EFAULT;
  96                 return -EINVAL;
  97         }
  98
  99         return 0;
 100 }
 101
 102 /*
 103  * The only thing that can change the capabilities of the current
 104  * process is the current process. As such, we can't be in this code
 105  * at the same time as we are in the process of setting capabilities
 106  * in this process. The net result is that we can limit our use of
 107  * locks to when we are reading the caps of another process.
 108  */
 109 static inline int cap_get_target_pid(pid_t pid, kernel_cap_t *pEp,
 110                                      kernel_cap_t *pIp, kernel_cap_t *pPp)
 111 {
 112         int ret;
 113
 114         if (pid && (pid != task_pid_vnr(current))) {
 115                 const struct task_struct *target;
 116
 117                 rcu_read_lock();
 118
 119                 target = find_task_by_vpid(pid);
 120                 if (!target)
 121                         ret = -ESRCH;
 122                 else
 123                         ret = security_capget(target, pEp, pIp, pPp);
 124
 125                 rcu_read_unlock();
 126         } else
 127                 ret = security_capget(current, pEp, pIp, pPp);
 128
 129         return ret;
 130 }
 131
 132 /**
 133  * sys_capget - get the capabilities of a given process.
 134  * @header: pointer to struct that contains capability version and
 135  *      target pid data
 136  * @dataptr: pointer to struct that contains the effective, permitted,
 137  *      and inheritable capabilities that are returned
 138  *
 139  * Returns 0 on success and < 0 on error.
 140  */
 141 SYSCALL_DEFINE2(capget, cap_user_header_t, header, cap_user_data_t, dataptr)
 142 {
 143         int ret = 0;
 144         pid_t pid;
 145         unsigned tocopy;
 146         kernel_cap_t pE, pI, pP;
 147         struct __user_cap_data_struct kdata[2];
 148
 149         ret = cap_validate_magic(header, &tocopy);
 150         if ((dataptr == NULL) || (ret != 0))
 151                 return ((dataptr == NULL) && (ret == -EINVAL)) ? 0 : ret;
 152
 153         if (get_user(pid, &header->pid))
 154                 return -EFAULT;
 155
 156         if (pid < 0)
 157                 return -EINVAL;
 158
 159         ret = cap_get_target_pid(pid, &pE, &pI, &pP);
 160         if (ret)
 161                 return ret;
 162
 163         /*
 164          * Annoying legacy format with 64-bit capabilities exposed
 165          * as two sets of 32-bit fields, so we need to split the
 166          * capability values up.
 167          */
 168         kdata[0].effective   = pE.val; kdata[1].effective   = pE.val >> 32;
 169         kdata[0].permitted   = pP.val; kdata[1].permitted   = pP.val >> 32;
 170         kdata[0].inheritable = pI.val; kdata[1].inheritable = pI.val >> 32;
 171
 172         /*
 173          * Note, in the case, tocopy < _KERNEL_CAPABILITY_U32S,
 174          * we silently drop the upper capabilities here. This
 175          * has the effect of making older libcap
 176          * implementations implicitly drop upper capability
 177          * bits when they perform a: capget/modify/capset
 178          * sequence.
 179          *
 180          * This behavior is considered fail-safe
 181          * behavior. Upgrading the application to a newer
 182          * version of libcap will enable access to the newer
 183          * capabilities.
 184          *
 185          * An alternative would be to return an error here
 186          * (-ERANGE), but that causes legacy applications to
 187          * unexpectedly fail; the capget/modify/capset aborts
 188          * before modification is attempted and the application
 189          * fails.
 190          */
 191         if (copy_to_user(dataptr, kdata, tocopy * sizeof(kdata[0])))
 192                 return -EFAULT;
 193
 194         return 0;
 195 }
 196
 197 static kernel_cap_t mk_kernel_cap(u32 low, u32 high)
 198 {
 199         return (kernel_cap_t) { (low | ((u64)high << 32)) & CAP_VALID_MASK };
 200 }
 201
 202 /**
 203  * sys_capset - set capabilities for a process or (*) a group of processes
 204  * @header: pointer to struct that contains capability version and
 205  *      target pid data
 206  * @data: pointer to struct that contains the effective, permitted,
 207  *      and inheritable capabilities
 208  *
 209  * Set capabilities for the current process only.  The ability to any other
 210  * process(es) has been deprecated and removed.
 211  *
 212  * The restrictions on setting capabilities are specified as:
 213  *
 214  * I: any raised capabilities must be a subset of the old permitted
 215  * P: any raised capabilities must be a subset of the old permitted
 216  * E: must be set to a subset of new permitted
 217  *
 218  * Returns 0 on success and < 0 on error.
 219  */
 220 SYSCALL_DEFINE2(capset, cap_user_header_t, header, const cap_user_data_t, data)
 221 {
 222         struct __user_cap_data_struct kdata[2] = { { 0, }, };
 223         unsigned tocopy, copybytes;
 224         kernel_cap_t inheritable, permitted, effective;
 225         struct cred *new;
 226         int ret;
 227         pid_t pid;
 228
 229         ret = cap_validate_magic(header, &tocopy);
 230         if (ret != 0)
 231                 return ret;
 232
 233         if (get_user(pid, &header->pid))
 234                 return -EFAULT;
 235
 236         /* may only affect current now */
 237         if (pid != 0 && pid != task_pid_vnr(current))
 238                 return -EPERM;
 239
 240         copybytes = tocopy * sizeof(struct __user_cap_data_struct);
 241         if (copybytes > sizeof(kdata))
 242                 return -EFAULT;
 243
 244         if (copy_from_user(&kdata, data, copybytes))
 245                 return -EFAULT;
 246
 247         effective   = mk_kernel_cap(kdata[0].effective,   kdata[1].effective);
 248         permitted   = mk_kernel_cap(kdata[0].permitted,   kdata[1].permitted);
 249         inheritable = mk_kernel_cap(kdata[0].inheritable, kdata[1].inheritable);
 250
 251         new = prepare_creds();
 252         if (!new)
 253                 return -ENOMEM;
 254
 255         ret = security_capset(new, current_cred(),
 256                               &effective, &inheritable, &permitted);
 257         if (ret < 0)
 258                 goto error;
 259
 260         audit_log_capset(new, current_cred());
 261
 262         return commit_creds(new);
 263
 264 error:
 265         abort_creds(new);
 266         return ret;
 267 }
 268
 269 /**
 270  * has_ns_capability - Does a task have a capability in a specific user ns
 271  * @t: The task in question
 272  * @ns: target user namespace
 273  * @cap: The capability to be tested for
 274  *
 275  * Return true if the specified task has the given superior capability
 276  * currently in effect to the specified user namespace, false if not.
 277  *
 278  * Note that this does not set PF_SUPERPRIV on the task.
 279  */
 280 bool has_ns_capability(struct task_struct *t,
 281                        struct user_namespace *ns, int cap)
 282 {
 283         int ret;
 284
 285         rcu_read_lock();
 286         ret = security_capable(__task_cred(t), ns, cap, CAP_OPT_NONE);
 287         rcu_read_unlock();
 288
 289         return (ret == 0);
 290 }
 291
 292 /**
 293  * has_capability - Does a task have a capability in init_user_ns
 294  * @t: The task in question
 295  * @cap: The capability to be tested for
 296  *
 297  * Return true if the specified task has the given superior capability
 298  * currently in effect to the initial user namespace, false if not.
 299  *
 300  * Note that this does not set PF_SUPERPRIV on the task.
 301  */
 302 bool has_capability(struct task_struct *t, int cap)
 303 {
 304         return has_ns_capability(t, &init_user_ns, cap);
 305 }
 306 EXPORT_SYMBOL(has_capability);
 307
 308 /**
 309  * has_ns_capability_noaudit - Does a task have a capability (unaudited)
 310  * in a specific user ns.
 311  * @t: The task in question
 312  * @ns: target user namespace
 313  * @cap: The capability to be tested for
 314  *
 315  * Return true if the specified task has the given superior capability
 316  * currently in effect to the specified user namespace, false if not.
 317  * Do not write an audit message for the check.
 318  *
 319  * Note that this does not set PF_SUPERPRIV on the task.
 320  */
 321 bool has_ns_capability_noaudit(struct task_struct *t,
 322                                struct user_namespace *ns, int cap)
 323 {
 324         int ret;
 325
 326         rcu_read_lock();
 327         ret = security_capable(__task_cred(t), ns, cap, CAP_OPT_NOAUDIT);
 328         rcu_read_unlock();
 329
 330         return (ret == 0);
 331 }
 332
 333 /**
 334  * has_capability_noaudit - Does a task have a capability (unaudited) in the
 335  * initial user ns
 336  * @t: The task in question
 337  * @cap: The capability to be tested for
 338  *
 339  * Return true if the specified task has the given superior capability
 340  * currently in effect to init_user_ns, false if not.  Don't write an
 341  * audit message for the check.
 342  *
 343  * Note that this does not set PF_SUPERPRIV on the task.
 344  */
 345 bool has_capability_noaudit(struct task_struct *t, int cap)
 346 {
 347         return has_ns_capability_noaudit(t, &init_user_ns, cap);
 348 }
 349 EXPORT_SYMBOL(has_capability_noaudit);
 350
 351 static bool ns_capable_common(struct user_namespace *ns,
 352                               int cap,
 353                               unsigned int opts)
 354 {
 355         int capable;
 356
 357         if (unlikely(!cap_valid(cap))) {
 358                 pr_crit("capable() called with invalid cap=%u\n", cap);
 359                 BUG();
 360         }
 361
 362         capable = security_capable(current_cred(), ns, cap, opts);
 363         if (capable == 0) {
 364                 current->flags |= PF_SUPERPRIV;
 365                 return true;
 366         }
 367         return false;
 368 }
 369
 370 /**
 371  * ns_capable - Determine if the current task has a superior capability in effect
 372  * @ns:  The usernamespace we want the capability in
 373  * @cap: The capability to be tested for
 374  *
 375  * Return true if the current task has the given superior capability currently
 376  * available for use, false if not.
 377  *
 378  * This sets PF_SUPERPRIV on the task if the capability is available on the
 379  * assumption that it's about to be used.
 380  */
 381 bool ns_capable(struct user_namespace *ns, int cap)
 382 {
 383         return ns_capable_common(ns, cap, CAP_OPT_NONE);
 384 }
 385 EXPORT_SYMBOL(ns_capable);
 386
 387 /**
 388  * ns_capable_noaudit - Determine if the current task has a superior capability
 389  * (unaudited) in effect
 390  * @ns:  The usernamespace we want the capability in
 391  * @cap: The capability to be tested for
 392  *
 393  * Return true if the current task has the given superior capability currently
 394  * available for use, false if not.
 395  *
 396  * This sets PF_SUPERPRIV on the task if the capability is available on the
 397  * assumption that it's about to be used.
 398  */
 399 bool ns_capable_noaudit(struct user_namespace *ns, int cap)
 400 {
 401         return ns_capable_common(ns, cap, CAP_OPT_NOAUDIT);
 402 }
 403 EXPORT_SYMBOL(ns_capable_noaudit);
 404
 405 /**
 406  * ns_capable_setid - Determine if the current task has a superior capability
 407  * in effect, while signalling that this check is being done from within a
 408  * setid or setgroups syscall.
 409  * @ns:  The usernamespace we want the capability in
 410  * @cap: The capability to be tested for
 411  *
 412  * Return true if the current task has the given superior capability currently
 413  * available for use, false if not.
 414  *
 415  * This sets PF_SUPERPRIV on the task if the capability is available on the
 416  * assumption that it's about to be used.
 417  */
 418 bool ns_capable_setid(struct user_namespace *ns, int cap)
 419 {
 420         return ns_capable_common(ns, cap, CAP_OPT_INSETID);
 421 }
 422 EXPORT_SYMBOL(ns_capable_setid);
 423
 424 /**
 425  * capable - Determine if the current task has a superior capability in effect
 426  * @cap: The capability to be tested for
 427  *
 428  * Return true if the current task has the given superior capability currently
 429  * available for use, false if not.
 430  *
 431  * This sets PF_SUPERPRIV on the task if the capability is available on the
 432  * assumption that it's about to be used.
 433  */
 434 bool capable(int cap)
 435 {
 436         return ns_capable(&init_user_ns, cap);
 437 }
 438 EXPORT_SYMBOL(capable);
 439 #endif /* CONFIG_MULTIUSER */
 440
 441 /**
 442  * file_ns_capable - Determine if the file's opener had a capability in effect
 443  * @file:  The file we want to check
 444  * @ns:  The usernamespace we want the capability in
 445  * @cap: The capability to be tested for
 446  *
 447  * Return true if task that opened the file had a capability in effect
 448  * when the file was opened.
 449  *
 450  * This does not set PF_SUPERPRIV because the caller may not
 451  * actually be privileged.
 452  */
 453 bool file_ns_capable(const struct file *file, struct user_namespace *ns,
 454                      int cap)
 455 {
 456
 457         if (WARN_ON_ONCE(!cap_valid(cap)))
 458                 return false;
 459
 460         if (security_capable(file->f_cred, ns, cap, CAP_OPT_NONE) == 0)
 461                 return true;
 462
 463         return false;
 464 }
 465 EXPORT_SYMBOL(file_ns_capable);
 466
 467 /**
 468  * privileged_wrt_inode_uidgid - Do capabilities in the namespace work over the inode?
 469  * @ns: The user namespace in question
 470  * @idmap: idmap of the mount @inode was found from
 471  * @inode: The inode in question
 472  *
 473  * Return true if the inode uid and gid are within the namespace.
 474  */
 475 bool privileged_wrt_inode_uidgid(struct user_namespace *ns,
 476                                  struct mnt_idmap *idmap,
 477                                  const struct inode *inode)
 478 {
 479         return vfsuid_has_mapping(ns, i_uid_into_vfsuid(idmap, inode)) &&
 480                vfsgid_has_mapping(ns, i_gid_into_vfsgid(idmap, inode));
 481 }
 482
 483 /**
 484  * capable_wrt_inode_uidgid - Check nsown_capable and uid and gid mapped
 485  * @idmap: idmap of the mount @inode was found from
 486  * @inode: The inode in question
 487  * @cap: The capability in question
 488  *
 489  * Return true if the current task has the given capability targeted at
 490  * its own user namespace and that the given inode's uid and gid are
 491  * mapped into the current user namespace.
 492  */
 493 bool capable_wrt_inode_uidgid(struct mnt_idmap *idmap,
 494                               const struct inode *inode, int cap)
 495 {
 496         struct user_namespace *ns = current_user_ns();
 497
 498         return ns_capable(ns, cap) &&
 499                privileged_wrt_inode_uidgid(ns, idmap, inode);
 500 }
 501 EXPORT_SYMBOL(capable_wrt_inode_uidgid);
 502
 503 /**
 504  * ptracer_capable - Determine if the ptracer holds CAP_SYS_PTRACE in the namespace
 505  * @tsk: The task that may be ptraced
 506  * @ns: The user namespace to search for CAP_SYS_PTRACE in
 507  *
 508  * Return true if the task that is ptracing the current task had CAP_SYS_PTRACE
 509  * in the specified user namespace.
 510  */
 511 bool ptracer_capable(struct task_struct *tsk, struct user_namespace *ns)
 512 {
 513         int ret = 0;  /* An absent tracer adds no restrictions */
 514         const struct cred *cred;
 515
 516         rcu_read_lock();
 517         cred = rcu_dereference(tsk->ptracer_cred);
 518         if (cred)
 519                 ret = security_capable(cred, ns, CAP_SYS_PTRACE,
 520                                        CAP_OPT_NOAUDIT);
 521         rcu_read_unlock();
 522         return (ret == 0);
 523 }