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