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#include <linux/audit.h>
11#include <linux/capability.h>
12#include <linux/mm.h>
13#include <linux/module.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
24const kernel_cap_t __cap_empty_set = CAP_EMPTY_SET;
25
26EXPORT_SYMBOL(__cap_empty_set);
27
28int file_caps_enabled = 1;
29
30static 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
43static 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
72static 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 */
90static 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 */
126static 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 */
158SYSCALL_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 */
232SYSCALL_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
284error:
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 */
299bool 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 */
317bool 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 */
336bool 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 */
353bool capable(int cap)
354{
355    return ns_capable(&init_user_ns, cap);
356}
357EXPORT_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 */
370bool 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}
383EXPORT_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 */
393bool task_ns_capable(struct task_struct *t, int cap)
394{
395    return ns_capable(task_cred_xxx(t, user)->user_ns, cap);
396}
397EXPORT_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 */
406bool nsown_capable(int cap)
407{
408    return ns_capable(current_user_ns(), cap);
409}
410

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