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Linux/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 <linux/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 #ifdef CONFIG_MULTIUSER
 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                  * unexpectedly 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         effective.cap[CAP_LAST_U32] &= CAP_LAST_U32_VALID_MASK;
263         permitted.cap[CAP_LAST_U32] &= CAP_LAST_U32_VALID_MASK;
264         inheritable.cap[CAP_LAST_U32] &= CAP_LAST_U32_VALID_MASK;
265 
266         new = prepare_creds();
267         if (!new)
268                 return -ENOMEM;
269 
270         ret = security_capset(new, current_cred(),
271                               &effective, &inheritable, &permitted);
272         if (ret < 0)
273                 goto error;
274 
275         audit_log_capset(new, current_cred());
276 
277         return commit_creds(new);
278 
279 error:
280         abort_creds(new);
281         return ret;
282 }
283 
284 /**
285  * has_ns_capability - Does a task have a capability in a specific user ns
286  * @t: The task in question
287  * @ns: target user namespace
288  * @cap: The capability to be tested for
289  *
290  * Return true if the specified task has the given superior capability
291  * currently in effect to the specified user namespace, false if not.
292  *
293  * Note that this does not set PF_SUPERPRIV on the task.
294  */
295 bool has_ns_capability(struct task_struct *t,
296                        struct user_namespace *ns, int cap)
297 {
298         int ret;
299 
300         rcu_read_lock();
301         ret = security_capable(__task_cred(t), ns, cap);
302         rcu_read_unlock();
303 
304         return (ret == 0);
305 }
306 
307 /**
308  * has_capability - Does a task have a capability in init_user_ns
309  * @t: The task in question
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 initial user namespace, false if not.
314  *
315  * Note that this does not set PF_SUPERPRIV on the task.
316  */
317 bool has_capability(struct task_struct *t, int cap)
318 {
319         return has_ns_capability(t, &init_user_ns, cap);
320 }
321 EXPORT_SYMBOL(has_capability);
322 
323 /**
324  * has_ns_capability_noaudit - Does a task have a capability (unaudited)
325  * in a specific user ns.
326  * @t: The task in question
327  * @ns: target user namespace
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 the specified user namespace, false if not.
332  * Do not write an audit message for the check.
333  *
334  * Note that this does not set PF_SUPERPRIV on the task.
335  */
336 bool has_ns_capability_noaudit(struct task_struct *t,
337                                struct user_namespace *ns, int cap)
338 {
339         int ret;
340 
341         rcu_read_lock();
342         ret = security_capable_noaudit(__task_cred(t), ns, cap);
343         rcu_read_unlock();
344 
345         return (ret == 0);
346 }
347 
348 /**
349  * has_capability_noaudit - Does a task have a capability (unaudited) in the
350  * initial user ns
351  * @t: The task in question
352  * @cap: The capability to be tested for
353  *
354  * Return true if the specified task has the given superior capability
355  * currently in effect to init_user_ns, false if not.  Don't write an
356  * audit message for the check.
357  *
358  * Note that this does not set PF_SUPERPRIV on the task.
359  */
360 bool has_capability_noaudit(struct task_struct *t, int cap)
361 {
362         return has_ns_capability_noaudit(t, &init_user_ns, cap);
363 }
364 
365 static bool ns_capable_common(struct user_namespace *ns, int cap, bool audit)
366 {
367         int capable;
368 
369         if (unlikely(!cap_valid(cap))) {
370                 pr_crit("capable() called with invalid cap=%u\n", cap);
371                 BUG();
372         }
373 
374         capable = audit ? security_capable(current_cred(), ns, cap) :
375                           security_capable_noaudit(current_cred(), ns, cap);
376         if (capable == 0) {
377                 current->flags |= PF_SUPERPRIV;
378                 return true;
379         }
380         return false;
381 }
382 
383 /**
384  * ns_capable - Determine if the current task has a superior capability in effect
385  * @ns:  The usernamespace we want the capability in
386  * @cap: The capability to be tested for
387  *
388  * Return true if the current task has the given superior capability currently
389  * available for use, false if not.
390  *
391  * This sets PF_SUPERPRIV on the task if the capability is available on the
392  * assumption that it's about to be used.
393  */
394 bool ns_capable(struct user_namespace *ns, int cap)
395 {
396         return ns_capable_common(ns, cap, true);
397 }
398 EXPORT_SYMBOL(ns_capable);
399 
400 /**
401  * ns_capable_noaudit - Determine if the current task has a superior capability
402  * (unaudited) in effect
403  * @ns:  The usernamespace we want the capability in
404  * @cap: The capability to be tested for
405  *
406  * Return true if the current task has the given superior capability currently
407  * available for use, false if not.
408  *
409  * This sets PF_SUPERPRIV on the task if the capability is available on the
410  * assumption that it's about to be used.
411  */
412 bool ns_capable_noaudit(struct user_namespace *ns, int cap)
413 {
414         return ns_capable_common(ns, cap, false);
415 }
416 EXPORT_SYMBOL(ns_capable_noaudit);
417 
418 /**
419  * capable - Determine if the current task has a superior capability in effect
420  * @cap: The capability to be tested for
421  *
422  * Return true if the current task has the given superior capability currently
423  * available for use, false if not.
424  *
425  * This sets PF_SUPERPRIV on the task if the capability is available on the
426  * assumption that it's about to be used.
427  */
428 bool capable(int cap)
429 {
430         return ns_capable(&init_user_ns, cap);
431 }
432 EXPORT_SYMBOL(capable);
433 #endif /* CONFIG_MULTIUSER */
434 
435 /**
436  * file_ns_capable - Determine if the file's opener had a capability in effect
437  * @file:  The file we want to check
438  * @ns:  The usernamespace we want the capability in
439  * @cap: The capability to be tested for
440  *
441  * Return true if task that opened the file had a capability in effect
442  * when the file was opened.
443  *
444  * This does not set PF_SUPERPRIV because the caller may not
445  * actually be privileged.
446  */
447 bool file_ns_capable(const struct file *file, struct user_namespace *ns,
448                      int cap)
449 {
450         if (WARN_ON_ONCE(!cap_valid(cap)))
451                 return false;
452 
453         if (security_capable(file->f_cred, ns, cap) == 0)
454                 return true;
455 
456         return false;
457 }
458 EXPORT_SYMBOL(file_ns_capable);
459 
460 /**
461  * privileged_wrt_inode_uidgid - Do capabilities in the namespace work over the inode?
462  * @ns: The user namespace in question
463  * @inode: The inode in question
464  *
465  * Return true if the inode uid and gid are within the namespace.
466  */
467 bool privileged_wrt_inode_uidgid(struct user_namespace *ns, const struct inode *inode)
468 {
469         return kuid_has_mapping(ns, inode->i_uid) &&
470                 kgid_has_mapping(ns, inode->i_gid);
471 }
472 
473 /**
474  * capable_wrt_inode_uidgid - Check nsown_capable and uid and gid mapped
475  * @inode: The inode in question
476  * @cap: The capability in question
477  *
478  * Return true if the current task has the given capability targeted at
479  * its own user namespace and that the given inode's uid and gid are
480  * mapped into the current user namespace.
481  */
482 bool capable_wrt_inode_uidgid(const struct inode *inode, int cap)
483 {
484         struct user_namespace *ns = current_user_ns();
485 
486         return ns_capable(ns, cap) && privileged_wrt_inode_uidgid(ns, inode);
487 }
488 EXPORT_SYMBOL(capable_wrt_inode_uidgid);
489 
490 /**
491  * ptracer_capable - Determine if the ptracer holds CAP_SYS_PTRACE in the namespace
492  * @tsk: The task that may be ptraced
493  * @ns: The user namespace to search for CAP_SYS_PTRACE in
494  *
495  * Return true if the task that is ptracing the current task had CAP_SYS_PTRACE
496  * in the specified user namespace.
497  */
498 bool ptracer_capable(struct task_struct *tsk, struct user_namespace *ns)
499 {
500         int ret = 0;  /* An absent tracer adds no restrictions */
501         const struct cred *cred;
502         rcu_read_lock();
503         cred = rcu_dereference(tsk->ptracer_cred);
504         if (cred)
505                 ret = security_capable_noaudit(cred, ns, CAP_SYS_PTRACE);
506         rcu_read_unlock();
507         return (ret == 0);
508 }
509 

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