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

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