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
  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 /*
  40  * More recent versions of libcap are available from:
  41  *
  42  *   http://www.kernel.org/pub/linux/libs/security/linux-privs/
  43  */
  44
  45 static 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
  69 static 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  */
  81 static 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  */
 117 static 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  */
 149 SYSCALL_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                  * unexpectidly 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  */
 223 SYSCALL_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         new = prepare_creds();
 263         if (!new)
 264                 return -ENOMEM;
 265
 266         ret = security_capset(new, current_cred(),
 267                               &effective, &inheritable, &permitted);
 268         if (ret < 0)
 269                 goto error;
 270
 271         audit_log_capset(new, current_cred());
 272
 273         return commit_creds(new);
 274
 275 error:
 276         abort_creds(new);
 277         return ret;
 278 }
 279
 280 /**
 281  * has_ns_capability - Does a task have a capability in a specific user ns
 282  * @t: The task in question
 283  * @ns: target user namespace
 284  * @cap: The capability to be tested for
 285  *
 286  * Return true if the specified task has the given superior capability
 287  * currently in effect to the specified user namespace, false if not.
 288  *
 289  * Note that this does not set PF_SUPERPRIV on the task.
 290  */
 291 bool has_ns_capability(struct task_struct *t,
 292                        struct user_namespace *ns, int cap)
 293 {
 294         int ret;
 295
 296         rcu_read_lock();
 297         ret = security_capable(__task_cred(t), ns, cap);
 298         rcu_read_unlock();
 299
 300         return (ret == 0);
 301 }
 302
 303 /**
 304  * has_capability - Does a task have a capability in init_user_ns
 305  * @t: The task in question
 306  * @cap: The capability to be tested for
 307  *
 308  * Return true if the specified task has the given superior capability
 309  * currently in effect to the initial user namespace, false if not.
 310  *
 311  * Note that this does not set PF_SUPERPRIV on the task.
 312  */
 313 bool has_capability(struct task_struct *t, int cap)
 314 {
 315         return has_ns_capability(t, &init_user_ns, cap);
 316 }
 317
 318 /**
 319  * has_ns_capability_noaudit - Does a task have a capability (unaudited)
 320  * in a specific user ns.
 321  * @t: The task in question
 322  * @ns: target user namespace
 323  * @cap: The capability to be tested for
 324  *
 325  * Return true if the specified task has the given superior capability
 326  * currently in effect to the specified user namespace, false if not.
 327  * Do not write an audit message for the check.
 328  *
 329  * Note that this does not set PF_SUPERPRIV on the task.
 330  */
 331 bool has_ns_capability_noaudit(struct task_struct *t,
 332                                struct user_namespace *ns, int cap)
 333 {
 334         int ret;
 335
 336         rcu_read_lock();
 337         ret = security_capable_noaudit(__task_cred(t), ns, cap);
 338         rcu_read_unlock();
 339
 340         return (ret == 0);
 341 }
 342
 343 /**
 344  * has_capability_noaudit - Does a task have a capability (unaudited) in the
 345  * initial user ns
 346  * @t: The task in question
 347  * @cap: The capability to be tested for
 348  *
 349  * Return true if the specified task has the given superior capability
 350  * currently in effect to init_user_ns, false if not.  Don't write an
 351  * audit message for the check.
 352  *
 353  * Note that this does not set PF_SUPERPRIV on the task.
 354  */
 355 bool has_capability_noaudit(struct task_struct *t, int cap)
 356 {
 357         return has_ns_capability_noaudit(t, &init_user_ns, cap);
 358 }
 359
 360 /**
 361  * ns_capable - Determine if the current task has a superior capability in effect
 362  * @ns:  The usernamespace we want the capability in
 363  * @cap: The capability to be tested for
 364  *
 365  * Return true if the current task has the given superior capability currently
 366  * available for use, false if not.
 367  *
 368  * This sets PF_SUPERPRIV on the task if the capability is available on the
 369  * assumption that it's about to be used.
 370  */
 371 bool ns_capable(struct user_namespace *ns, int cap)
 372 {
 373         if (unlikely(!cap_valid(cap))) {
 374                 pr_crit("capable() called with invalid cap=%u\n", cap);
 375                 BUG();
 376         }
 377
 378         if (security_capable(current_cred(), ns, cap) == 0) {
 379                 current->flags |= PF_SUPERPRIV;
 380                 return true;
 381         }
 382         return false;
 383 }
 384 EXPORT_SYMBOL(ns_capable);
 385
 386 /**
 387  * file_ns_capable - Determine if the file's opener had a capability in effect
 388  * @file:  The file we want to check
 389  * @ns:  The usernamespace we want the capability in
 390  * @cap: The capability to be tested for
 391  *
 392  * Return true if task that opened the file had a capability in effect
 393  * when the file was opened.
 394  *
 395  * This does not set PF_SUPERPRIV because the caller may not
 396  * actually be privileged.
 397  */
 398 bool file_ns_capable(const struct file *file, struct user_namespace *ns, 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  * inode_capable - Check superior capability over inode
 428  * @inode: The inode in question
 429  * @cap: The capability in question
 430  *
 431  * Return true if the current task has the given superior capability
 432  * targeted at it's own user namespace and that the given inode is owned
 433  * by the current user namespace or a child namespace.
 434  *
 435  * Currently we check to see if an inode is owned by the current
 436  * user namespace by seeing if the inode's owner maps into the
 437  * current user namespace.
 438  *
 439  */
 440 bool inode_capable(const struct inode *inode, int cap)
 441 {
 442         struct user_namespace *ns = current_user_ns();
 443
 444         return ns_capable(ns, cap) && kuid_has_mapping(ns, inode->i_uid);
 445 }
 446 EXPORT_SYMBOL(inode_capable);