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 #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
  26 const kernel_cap_t __cap_empty_set = CAP_EMPTY_SET;
  27 EXPORT_SYMBOL(__cap_empty_set);
  28
  29 int file_caps_enabled = 1;
  30
  31 static 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 /*
  39  * More recent versions of libcap are available from:
  40  *
  41  *   http://www.kernel.org/pub/linux/libs/security/linux-privs/
  42  */
  43
  44 static void warn_legacy_capability_use(void)
  45 {
  46         char name[sizeof(current->comm)];
  47
  48         pr_info_once("warning: `%s' uses 32-bit capabilities (legacy support in use)\n",
  49                      get_task_comm(name, current));
  50 }
  51
  52 /*
  53  * Version 2 capabilities worked fine, but the linux/capability.h file
  54  * that accompanied their introduction encouraged their use without
  55  * the necessary user-space source code changes. As such, we have
  56  * created a version 3 with equivalent functionality to version 2, but
  57  * with a header change to protect legacy source code from using
  58  * version 2 when it wanted to use version 1. If your system has code
  59  * that trips the following warning, it is using version 2 specific
  60  * capabilities and may be doing so insecurely.
  61  *
  62  * The remedy is to either upgrade your version of libcap (to 2.10+,
  63  * if the application is linked against it), or recompile your
  64  * application with modern kernel headers and this warning will go
  65  * away.
  66  */
  67
  68 static void warn_deprecated_v2(void)
  69 {
  70         char name[sizeof(current->comm)];
  71
  72         pr_info_once("warning: `%s' uses deprecated v2 capabilities in a way that may be insecure\n",
  73                      get_task_comm(name, current));
  74 }
  75
  76 /*
  77  * Version check. Return the number of u32s in each capability flag
  78  * array, or a negative value on error.
  79  */
  80 static int cap_validate_magic(cap_user_header_t header, unsigned *tocopy)
  81 {
  82         __u32 version;
  83
  84         if (get_user(version, &header->version))
  85                 return -EFAULT;
  86
  87         switch (version) {
  88         case _LINUX_CAPABILITY_VERSION_1:
  89                 warn_legacy_capability_use();
  90                 *tocopy = _LINUX_CAPABILITY_U32S_1;
  91                 break;
  92         case _LINUX_CAPABILITY_VERSION_2:
  93                 warn_deprecated_v2();
  94                 /*
  95                  * fall through - v3 is otherwise equivalent to v2.
  96                  */
  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         new = prepare_creds();
 262         if (!new)
 263                 return -ENOMEM;
 264
 265         ret = security_capset(new, current_cred(),
 266                               &effective, &inheritable, &permitted);
 267         if (ret < 0)
 268                 goto error;
 269
 270         audit_log_capset(new, current_cred());
 271
 272         return commit_creds(new);
 273
 274 error:
 275         abort_creds(new);
 276         return ret;
 277 }
 278
 279 /**
 280  * has_ns_capability - Does a task have a capability in a specific user ns
 281  * @t: The task in question
 282  * @ns: target user namespace
 283  * @cap: The capability to be tested for
 284  *
 285  * Return true if the specified task has the given superior capability
 286  * currently in effect to the specified user namespace, false if not.
 287  *
 288  * Note that this does not set PF_SUPERPRIV on the task.
 289  */
 290 bool has_ns_capability(struct task_struct *t,
 291                        struct user_namespace *ns, int cap)
 292 {
 293         int ret;
 294
 295         rcu_read_lock();
 296         ret = security_capable(__task_cred(t), ns, cap);
 297         rcu_read_unlock();
 298
 299         return (ret == 0);
 300 }
 301
 302 /**
 303  * has_capability - Does a task have a capability in init_user_ns
 304  * @t: The task in question
 305  * @cap: The capability to be tested for
 306  *
 307  * Return true if the specified task has the given superior capability
 308  * currently in effect to the initial user namespace, false if not.
 309  *
 310  * Note that this does not set PF_SUPERPRIV on the task.
 311  */
 312 bool has_capability(struct task_struct *t, int cap)
 313 {
 314         return has_ns_capability(t, &init_user_ns, cap);
 315 }
 316
 317 /**
 318  * has_ns_capability_noaudit - Does a task have a capability (unaudited)
 319  * in a specific user ns.
 320  * @t: The task in question
 321  * @ns: target user namespace
 322  * @cap: The capability to be tested for
 323  *
 324  * Return true if the specified task has the given superior capability
 325  * currently in effect to the specified user namespace, false if not.
 326  * Do not write an audit message for the check.
 327  *
 328  * Note that this does not set PF_SUPERPRIV on the task.
 329  */
 330 bool has_ns_capability_noaudit(struct task_struct *t,
 331                                struct user_namespace *ns, int cap)
 332 {
 333         int ret;
 334
 335         rcu_read_lock();
 336         ret = security_capable_noaudit(__task_cred(t), ns, cap);
 337         rcu_read_unlock();
 338
 339         return (ret == 0);
 340 }
 341
 342 /**
 343  * has_capability_noaudit - Does a task have a capability (unaudited) in the
 344  * initial user ns
 345  * @t: The task in question
 346  * @cap: The capability to be tested for
 347  *
 348  * Return true if the specified task has the given superior capability
 349  * currently in effect to init_user_ns, false if not.  Don't write an
 350  * audit message for the check.
 351  *
 352  * Note that this does not set PF_SUPERPRIV on the task.
 353  */
 354 bool has_capability_noaudit(struct task_struct *t, int cap)
 355 {
 356         return has_ns_capability_noaudit(t, &init_user_ns, cap);
 357 }
 358
 359 /**
 360  * ns_capable - Determine if the current task has a superior capability in effect
 361  * @ns:  The usernamespace we want the capability in
 362  * @cap: The capability to be tested for
 363  *
 364  * Return true if the current task has the given superior capability currently
 365  * available for use, false if not.
 366  *
 367  * This sets PF_SUPERPRIV on the task if the capability is available on the
 368  * assumption that it's about to be used.
 369  */
 370 bool ns_capable(struct user_namespace *ns, int cap)
 371 {
 372         if (unlikely(!cap_valid(cap))) {
 373                 pr_crit("capable() called with invalid cap=%u\n", cap);
 374                 BUG();
 375         }
 376
 377         if (security_capable(current_cred(), ns, cap) == 0) {
 378                 current->flags |= PF_SUPERPRIV;
 379                 return true;
 380         }
 381         return false;
 382 }
 383 EXPORT_SYMBOL(ns_capable);
 384
 385 /**
 386  * file_ns_capable - Determine if the file's opener had a capability in effect
 387  * @file:  The file we want to check
 388  * @ns:  The usernamespace we want the capability in
 389  * @cap: The capability to be tested for
 390  *
 391  * Return true if task that opened the file had a capability in effect
 392  * when the file was opened.
 393  *
 394  * This does not set PF_SUPERPRIV because the caller may not
 395  * actually be privileged.
 396  */
 397 bool file_ns_capable(const struct file *file, struct user_namespace *ns,
 398                      int cap)
 399 {
 400         if (WARN_ON_ONCE(!cap_valid(cap)))
 401                 return false;
 402
 403         if (security_capable(file->f_cred, ns, cap) == 0)
 404                 return true;
 405
 406         return false;
 407 }
 408 EXPORT_SYMBOL(file_ns_capable);
 409
 410 /**
 411  * capable - Determine if the current task has a superior capability in effect
 412  * @cap: The capability to be tested for
 413  *
 414  * Return true if the current task has the given superior capability currently
 415  * available for use, false if not.
 416  *
 417  * This sets PF_SUPERPRIV on the task if the capability is available on the
 418  * assumption that it's about to be used.
 419  */
 420 bool capable(int cap)
 421 {
 422         return ns_capable(&init_user_ns, cap);
 423 }
 424 EXPORT_SYMBOL(capable);
 425
 426 /**
 427  * capable_wrt_inode_uidgid - Check nsown_capable and uid and gid mapped
 428  * @inode: The inode in question
 429  * @cap: The capability in question
 430  *
 431  * Return true if the current task has the given capability targeted at
 432  * its own user namespace and that the given inode's uid and gid are
 433  * mapped into the current user namespace.
 434  */
 435 bool capable_wrt_inode_uidgid(const struct inode *inode, int cap)
 436 {
 437         struct user_namespace *ns = current_user_ns();
 438
 439         return ns_capable(ns, cap) && kuid_has_mapping(ns, inode->i_uid) &&
 440                 kgid_has_mapping(ns, inode->i_gid);
 441 }
 442 EXPORT_SYMBOL(capable_wrt_inode_uidgid);