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 #include <linux/audit.h>
  11 #include <linux/capability.h>
  12 #include <linux/mm.h>
  13 #include <linux/export.h>
  14 #include <linux/security.h>
  15 #include <linux/syscalls.h>
  16 #include <linux/pid_namespace.h>
  17 #include <linux/user_namespace.h>
  18 #include <asm/uaccess.h>
  19
  20 /*
  21  * Leveraged for setting/resetting capabilities
  22  */
  23
  24 const kernel_cap_t __cap_empty_set = CAP_EMPTY_SET;
  25
  26 EXPORT_SYMBOL(__cap_empty_set);
  27
  28 int file_caps_enabled = 1;
  29
  30 static int __init file_caps_disable(char *str)
  31 {
  32         file_caps_enabled = 0;
  33         return 1;
  34 }
  35 __setup("no_file_caps", file_caps_disable);
  36
  37 /*
  38  * More recent versions of libcap are available from:
  39  *
  40  *   http://www.kernel.org/pub/linux/libs/security/linux-privs/
  41  */
  42
  43 static void warn_legacy_capability_use(void)
  44 {
  45         static int warned;
  46         if (!warned) {
  47                 char name[sizeof(current->comm)];
  48
  49                 printk(KERN_INFO "warning: `%s' uses 32-bit capabilities"
  50                        " (legacy support in use)\n",
  51                        get_task_comm(name, current));
  52                 warned = 1;
  53         }
  54 }
  55
  56 /*
  57  * Version 2 capabilities worked fine, but the linux/capability.h file
  58  * that accompanied their introduction encouraged their use without
  59  * the necessary user-space source code changes. As such, we have
  60  * created a version 3 with equivalent functionality to version 2, but
  61  * with a header change to protect legacy source code from using
  62  * version 2 when it wanted to use version 1. If your system has code
  63  * that trips the following warning, it is using version 2 specific
  64  * capabilities and may be doing so insecurely.
  65  *
  66  * The remedy is to either upgrade your version of libcap (to 2.10+,
  67  * if the application is linked against it), or recompile your
  68  * application with modern kernel headers and this warning will go
  69  * away.
  70  */
  71
  72 static void warn_deprecated_v2(void)
  73 {
  74         static int warned;
  75
  76         if (!warned) {
  77                 char name[sizeof(current->comm)];
  78
  79                 printk(KERN_INFO "warning: `%s' uses deprecated v2"
  80                        " capabilities in a way that may be insecure.\n",
  81                        get_task_comm(name, current));
  82                 warned = 1;
  83         }
  84 }
  85
  86 /*
  87  * Version check. Return the number of u32s in each capability flag
  88  * array, or a negative value on error.
  89  */
  90 static int cap_validate_magic(cap_user_header_t header, unsigned *tocopy)
  91 {
  92         __u32 version;
  93
  94         if (get_user(version, &header->version))
  95                 return -EFAULT;
  96
  97         switch (version) {
  98         case _LINUX_CAPABILITY_VERSION_1:
  99                 warn_legacy_capability_use();
 100                 *tocopy = _LINUX_CAPABILITY_U32S_1;
 101                 break;
 102         case _LINUX_CAPABILITY_VERSION_2:
 103                 warn_deprecated_v2();
 104                 /*
 105                  * fall through - v3 is otherwise equivalent to v2.
 106                  */
 107         case _LINUX_CAPABILITY_VERSION_3:
 108                 *tocopy = _LINUX_CAPABILITY_U32S_3;
 109                 break;
 110         default:
 111                 if (put_user((u32)_KERNEL_CAPABILITY_VERSION, &header->version))
 112                         return -EFAULT;
 113                 return -EINVAL;
 114         }
 115
 116         return 0;
 117 }
 118
 119 /*
 120  * The only thing that can change the capabilities of the current
 121  * process is the current process. As such, we can't be in this code
 122  * at the same time as we are in the process of setting capabilities
 123  * in this process. The net result is that we can limit our use of
 124  * locks to when we are reading the caps of another process.
 125  */
 126 static inline int cap_get_target_pid(pid_t pid, kernel_cap_t *pEp,
 127                                      kernel_cap_t *pIp, kernel_cap_t *pPp)
 128 {
 129         int ret;
 130
 131         if (pid && (pid != task_pid_vnr(current))) {
 132                 struct task_struct *target;
 133
 134                 rcu_read_lock();
 135
 136                 target = find_task_by_vpid(pid);
 137                 if (!target)
 138                         ret = -ESRCH;
 139                 else
 140                         ret = security_capget(target, pEp, pIp, pPp);
 141
 142                 rcu_read_unlock();
 143         } else
 144                 ret = security_capget(current, pEp, pIp, pPp);
 145
 146         return ret;
 147 }
 148
 149 /**
 150  * sys_capget - get the capabilities of a given process.
 151  * @header: pointer to struct that contains capability version and
 152  *      target pid data
 153  * @dataptr: pointer to struct that contains the effective, permitted,
 154  *      and inheritable capabilities that are returned
 155  *
 156  * Returns 0 on success and < 0 on error.
 157  */
 158 SYSCALL_DEFINE2(capget, cap_user_header_t, header, cap_user_data_t, dataptr)
 159 {
 160         int ret = 0;
 161         pid_t pid;
 162         unsigned tocopy;
 163         kernel_cap_t pE, pI, pP;
 164
 165         ret = cap_validate_magic(header, &tocopy);
 166         if ((dataptr == NULL) || (ret != 0))
 167                 return ((dataptr == NULL) && (ret == -EINVAL)) ? 0 : ret;
 168
 169         if (get_user(pid, &header->pid))
 170                 return -EFAULT;
 171
 172         if (pid < 0)
 173                 return -EINVAL;
 174
 175         ret = cap_get_target_pid(pid, &pE, &pI, &pP);
 176         if (!ret) {
 177                 struct __user_cap_data_struct kdata[_KERNEL_CAPABILITY_U32S];
 178                 unsigned i;
 179
 180                 for (i = 0; i < tocopy; i++) {
 181                         kdata[i].effective = pE.cap[i];
 182                         kdata[i].permitted = pP.cap[i];
 183                         kdata[i].inheritable = pI.cap[i];
 184                 }
 185
 186                 /*
 187                  * Note, in the case, tocopy < _KERNEL_CAPABILITY_U32S,
 188                  * we silently drop the upper capabilities here. This
 189                  * has the effect of making older libcap
 190                  * implementations implicitly drop upper capability
 191                  * bits when they perform a: capget/modify/capset
 192                  * sequence.
 193                  *
 194                  * This behavior is considered fail-safe
 195                  * behavior. Upgrading the application to a newer
 196                  * version of libcap will enable access to the newer
 197                  * capabilities.
 198                  *
 199                  * An alternative would be to return an error here
 200                  * (-ERANGE), but that causes legacy applications to
 201                  * unexpectidly fail; the capget/modify/capset aborts
 202                  * before modification is attempted and the application
 203                  * fails.
 204                  */
 205                 if (copy_to_user(dataptr, kdata, tocopy
 206                                  * sizeof(struct __user_cap_data_struct))) {
 207                         return -EFAULT;
 208                 }
 209         }
 210
 211         return ret;
 212 }
 213
 214 /**
 215  * sys_capset - set capabilities for a process or (*) a group of processes
 216  * @header: pointer to struct that contains capability version and
 217  *      target pid data
 218  * @data: pointer to struct that contains the effective, permitted,
 219  *      and inheritable capabilities
 220  *
 221  * Set capabilities for the current process only.  The ability to any other
 222  * process(es) has been deprecated and removed.
 223  *
 224  * The restrictions on setting capabilities are specified as:
 225  *
 226  * I: any raised capabilities must be a subset of the old permitted
 227  * P: any raised capabilities must be a subset of the old permitted
 228  * E: must be set to a subset of new permitted
 229  *
 230  * Returns 0 on success and < 0 on error.
 231  */
 232 SYSCALL_DEFINE2(capset, cap_user_header_t, header, const cap_user_data_t, data)
 233 {
 234         struct __user_cap_data_struct kdata[_KERNEL_CAPABILITY_U32S];
 235         unsigned i, tocopy, copybytes;
 236         kernel_cap_t inheritable, permitted, effective;
 237         struct cred *new;
 238         int ret;
 239         pid_t pid;
 240
 241         ret = cap_validate_magic(header, &tocopy);
 242         if (ret != 0)
 243                 return ret;
 244
 245         if (get_user(pid, &header->pid))
 246                 return -EFAULT;
 247
 248         /* may only affect current now */
 249         if (pid != 0 && pid != task_pid_vnr(current))
 250                 return -EPERM;
 251
 252         copybytes = tocopy * sizeof(struct __user_cap_data_struct);
 253         if (copybytes > sizeof(kdata))
 254                 return -EFAULT;
 255
 256         if (copy_from_user(&kdata, data, copybytes))
 257                 return -EFAULT;
 258
 259         for (i = 0; i < tocopy; i++) {
 260                 effective.cap[i] = kdata[i].effective;
 261                 permitted.cap[i] = kdata[i].permitted;
 262                 inheritable.cap[i] = kdata[i].inheritable;
 263         }
 264         while (i < _KERNEL_CAPABILITY_U32S) {
 265                 effective.cap[i] = 0;
 266                 permitted.cap[i] = 0;
 267                 inheritable.cap[i] = 0;
 268                 i++;
 269         }
 270
 271         new = prepare_creds();
 272         if (!new)
 273                 return -ENOMEM;
 274
 275         ret = security_capset(new, current_cred(),
 276                               &effective, &inheritable, &permitted);
 277         if (ret < 0)
 278                 goto error;
 279
 280         audit_log_capset(pid, new, current_cred());
 281
 282         return commit_creds(new);
 283
 284 error:
 285         abort_creds(new);
 286         return ret;
 287 }
 288
 289 /**
 290  * has_capability - Does a task have a capability in init_user_ns
 291  * @t: The task in question
 292  * @cap: The capability to be tested for
 293  *
 294  * Return true if the specified task has the given superior capability
 295  * currently in effect to the initial user namespace, false if not.
 296  *
 297  * Note that this does not set PF_SUPERPRIV on the task.
 298  */
 299 bool has_capability(struct task_struct *t, int cap)
 300 {
 301         int ret = security_real_capable(t, &init_user_ns, cap);
 302
 303         return (ret == 0);
 304 }
 305
 306 /**
 307  * has_capability - Does a task have a capability in a specific user ns
 308  * @t: The task in question
 309  * @ns: target user namespace
 310  * @cap: The capability to be tested for
 311  *
 312  * Return true if the specified task has the given superior capability
 313  * currently in effect to the specified user namespace, false if not.
 314  *
 315  * Note that this does not set PF_SUPERPRIV on the task.
 316  */
 317 bool has_ns_capability(struct task_struct *t,
 318                        struct user_namespace *ns, int cap)
 319 {
 320         int ret = security_real_capable(t, ns, cap);
 321
 322         return (ret == 0);
 323 }
 324
 325 /**
 326  * has_capability_noaudit - Does a task have a capability (unaudited)
 327  * @t: The task in question
 328  * @cap: The capability to be tested for
 329  *
 330  * Return true if the specified task has the given superior capability
 331  * currently in effect to init_user_ns, false if not.  Don't write an
 332  * audit message for the check.
 333  *
 334  * Note that this does not set PF_SUPERPRIV on the task.
 335  */
 336 bool has_capability_noaudit(struct task_struct *t, int cap)
 337 {
 338         int ret = security_real_capable_noaudit(t, &init_user_ns, cap);
 339
 340         return (ret == 0);
 341 }
 342
 343 /**
 344  * capable - Determine if the current task has a superior capability in effect
 345  * @cap: The capability to be tested for
 346  *
 347  * Return true if the current task has the given superior capability currently
 348  * available for use, false if not.
 349  *
 350  * This sets PF_SUPERPRIV on the task if the capability is available on the
 351  * assumption that it's about to be used.
 352  */
 353 bool capable(int cap)
 354 {
 355         return ns_capable(&init_user_ns, cap);
 356 }
 357 EXPORT_SYMBOL(capable);
 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                 printk(KERN_CRIT "capable() called with invalid cap=%u\n", cap);
 374                 BUG();
 375         }
 376
 377         if (security_capable(ns, current_cred(), cap) == 0) {
 378                 current->flags |= PF_SUPERPRIV;
 379                 return true;
 380         }
 381         return false;
 382 }
 383 EXPORT_SYMBOL(ns_capable);
 384
 385 /**
 386  * task_ns_capable - Determine whether current task has a superior
 387  * capability targeted at a specific task's user namespace.
 388  * @t: The task whose user namespace is targeted.
 389  * @cap: The capability in question.
 390  *
 391  *  Return true if it does, false otherwise.
 392  */
 393 bool task_ns_capable(struct task_struct *t, int cap)
 394 {
 395         return ns_capable(task_cred_xxx(t, user)->user_ns, cap);
 396 }
 397 EXPORT_SYMBOL(task_ns_capable);
 398
 399 /**
 400  * nsown_capable - Check superior capability to one's own user_ns
 401  * @cap: The capability in question
 402  *
 403  * Return true if the current task has the given superior capability
 404  * targeted at its own user namespace.
 405  */
 406 bool nsown_capable(int cap)
 407 {
 408         return ns_capable(current_user_ns(), cap);
 409 }