Root/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
26const kernel_cap_t __cap_empty_set = CAP_EMPTY_SET;
27
28EXPORT_SYMBOL(__cap_empty_set);
29
30int file_caps_enabled = 1;
31
32static 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
45static 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
69static 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 */
81static 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 */
117static 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 */
149SYSCALL_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 */
223SYSCALL_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
275error:
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 */
291bool 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 */
313bool 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 */
331bool 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 */
355bool 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 */
371bool 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}
384EXPORT_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 */
398bool 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}
408EXPORT_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 */
420bool capable(int cap)
421{
422    return ns_capable(&init_user_ns, cap);
423}
424EXPORT_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 */
440bool 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}
446EXPORT_SYMBOL(inode_capable);
447

Archive Download this file



interactive