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