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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 
26 const kernel_cap_t __cap_empty_set = CAP_EMPTY_SET;
27 EXPORT_SYMBOL(__cap_empty_set);
28 
29 int file_caps_enabled = 1;
30 
file_caps_disable(char * str)31 static int __init file_caps_disable(char *str)
32 {
33 	file_caps_enabled = 0;
34 	return 1;
35 }
36 __setup("no_file_caps", file_caps_disable);
37 
38 #ifdef CONFIG_MULTIUSER
39 /*
40  * More recent versions of libcap are available from:
41  *
42  *   http://www.kernel.org/pub/linux/libs/security/linux-privs/
43  */
44 
warn_legacy_capability_use(void)45 static 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 
warn_deprecated_v2(void)69 static 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  */
cap_validate_magic(cap_user_header_t header,unsigned * tocopy)81 static 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  */
cap_get_target_pid(pid_t pid,kernel_cap_t * pEp,kernel_cap_t * pIp,kernel_cap_t * pPp)117 static 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  */
SYSCALL_DEFINE2(capget,cap_user_header_t,header,cap_user_data_t,dataptr)149 SYSCALL_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 		 * unexpectedly 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  */
SYSCALL_DEFINE2(capset,cap_user_header_t,header,const cap_user_data_t,data)223 SYSCALL_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 	effective.cap[CAP_LAST_U32] &= CAP_LAST_U32_VALID_MASK;
263 	permitted.cap[CAP_LAST_U32] &= CAP_LAST_U32_VALID_MASK;
264 	inheritable.cap[CAP_LAST_U32] &= CAP_LAST_U32_VALID_MASK;
265 
266 	new = prepare_creds();
267 	if (!new)
268 		return -ENOMEM;
269 
270 	ret = security_capset(new, current_cred(),
271 			      &effective, &inheritable, &permitted);
272 	if (ret < 0)
273 		goto error;
274 
275 	audit_log_capset(new, current_cred());
276 
277 	return commit_creds(new);
278 
279 error:
280 	abort_creds(new);
281 	return ret;
282 }
283 
284 /**
285  * has_ns_capability - Does a task have a capability in a specific user ns
286  * @t: The task in question
287  * @ns: target user namespace
288  * @cap: The capability to be tested for
289  *
290  * Return true if the specified task has the given superior capability
291  * currently in effect to the specified user namespace, false if not.
292  *
293  * Note that this does not set PF_SUPERPRIV on the task.
294  */
has_ns_capability(struct task_struct * t,struct user_namespace * ns,int cap)295 bool has_ns_capability(struct task_struct *t,
296 		       struct user_namespace *ns, int cap)
297 {
298 	int ret;
299 
300 	rcu_read_lock();
301 	ret = security_capable(__task_cred(t), ns, cap);
302 	rcu_read_unlock();
303 
304 	return (ret == 0);
305 }
306 
307 /**
308  * has_capability - Does a task have a capability in init_user_ns
309  * @t: The task in question
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 initial user namespace, false if not.
314  *
315  * Note that this does not set PF_SUPERPRIV on the task.
316  */
has_capability(struct task_struct * t,int cap)317 bool has_capability(struct task_struct *t, int cap)
318 {
319 	return has_ns_capability(t, &init_user_ns, cap);
320 }
321 
322 /**
323  * has_ns_capability_noaudit - Does a task have a capability (unaudited)
324  * in a specific user ns.
325  * @t: The task in question
326  * @ns: target user namespace
327  * @cap: The capability to be tested for
328  *
329  * Return true if the specified task has the given superior capability
330  * currently in effect to the specified user namespace, false if not.
331  * Do not write an audit message for the check.
332  *
333  * Note that this does not set PF_SUPERPRIV on the task.
334  */
has_ns_capability_noaudit(struct task_struct * t,struct user_namespace * ns,int cap)335 bool has_ns_capability_noaudit(struct task_struct *t,
336 			       struct user_namespace *ns, int cap)
337 {
338 	int ret;
339 
340 	rcu_read_lock();
341 	ret = security_capable_noaudit(__task_cred(t), ns, cap);
342 	rcu_read_unlock();
343 
344 	return (ret == 0);
345 }
346 
347 /**
348  * has_capability_noaudit - Does a task have a capability (unaudited) in the
349  * initial user ns
350  * @t: The task in question
351  * @cap: The capability to be tested for
352  *
353  * Return true if the specified task has the given superior capability
354  * currently in effect to init_user_ns, false if not.  Don't write an
355  * audit message for the check.
356  *
357  * Note that this does not set PF_SUPERPRIV on the task.
358  */
has_capability_noaudit(struct task_struct * t,int cap)359 bool has_capability_noaudit(struct task_struct *t, int cap)
360 {
361 	return has_ns_capability_noaudit(t, &init_user_ns, cap);
362 }
363 
ns_capable_common(struct user_namespace * ns,int cap,bool audit)364 static bool ns_capable_common(struct user_namespace *ns, int cap, bool audit)
365 {
366 	int capable;
367 
368 	if (unlikely(!cap_valid(cap))) {
369 		pr_crit("capable() called with invalid cap=%u\n", cap);
370 		BUG();
371 	}
372 
373 	capable = audit ? security_capable(current_cred(), ns, cap) :
374 			  security_capable_noaudit(current_cred(), ns, cap);
375 	if (capable == 0) {
376 		current->flags |= PF_SUPERPRIV;
377 		return true;
378 	}
379 	return false;
380 }
381 
382 /**
383  * ns_capable - Determine if the current task has a superior capability in effect
384  * @ns:  The usernamespace we want the capability in
385  * @cap: The capability to be tested for
386  *
387  * Return true if the current task has the given superior capability currently
388  * available for use, false if not.
389  *
390  * This sets PF_SUPERPRIV on the task if the capability is available on the
391  * assumption that it's about to be used.
392  */
ns_capable(struct user_namespace * ns,int cap)393 bool ns_capable(struct user_namespace *ns, int cap)
394 {
395 	return ns_capable_common(ns, cap, true);
396 }
397 EXPORT_SYMBOL(ns_capable);
398 
399 /**
400  * ns_capable_noaudit - Determine if the current task has a superior capability
401  * (unaudited) in effect
402  * @ns:  The usernamespace we want the capability in
403  * @cap: The capability to be tested for
404  *
405  * Return true if the current task has the given superior capability currently
406  * available for use, false if not.
407  *
408  * This sets PF_SUPERPRIV on the task if the capability is available on the
409  * assumption that it's about to be used.
410  */
ns_capable_noaudit(struct user_namespace * ns,int cap)411 bool ns_capable_noaudit(struct user_namespace *ns, int cap)
412 {
413 	return ns_capable_common(ns, cap, false);
414 }
415 EXPORT_SYMBOL(ns_capable_noaudit);
416 
417 /**
418  * capable - Determine if the current task has a superior capability in effect
419  * @cap: The capability to be tested for
420  *
421  * Return true if the current task has the given superior capability currently
422  * available for use, false if not.
423  *
424  * This sets PF_SUPERPRIV on the task if the capability is available on the
425  * assumption that it's about to be used.
426  */
capable(int cap)427 bool capable(int cap)
428 {
429 	return ns_capable(&init_user_ns, cap);
430 }
431 EXPORT_SYMBOL(capable);
432 #endif /* CONFIG_MULTIUSER */
433 
434 /**
435  * file_ns_capable - Determine if the file's opener had a capability in effect
436  * @file:  The file we want to check
437  * @ns:  The usernamespace we want the capability in
438  * @cap: The capability to be tested for
439  *
440  * Return true if task that opened the file had a capability in effect
441  * when the file was opened.
442  *
443  * This does not set PF_SUPERPRIV because the caller may not
444  * actually be privileged.
445  */
file_ns_capable(const struct file * file,struct user_namespace * ns,int cap)446 bool file_ns_capable(const struct file *file, struct user_namespace *ns,
447 		     int cap)
448 {
449 	if (WARN_ON_ONCE(!cap_valid(cap)))
450 		return false;
451 
452 	if (security_capable(file->f_cred, ns, cap) == 0)
453 		return true;
454 
455 	return false;
456 }
457 EXPORT_SYMBOL(file_ns_capable);
458 
459 /**
460  * privileged_wrt_inode_uidgid - Do capabilities in the namespace work over the inode?
461  * @ns: The user namespace in question
462  * @inode: The inode in question
463  *
464  * Return true if the inode uid and gid are within the namespace.
465  */
privileged_wrt_inode_uidgid(struct user_namespace * ns,const struct inode * inode)466 bool privileged_wrt_inode_uidgid(struct user_namespace *ns, const struct inode *inode)
467 {
468 	return kuid_has_mapping(ns, inode->i_uid) &&
469 		kgid_has_mapping(ns, inode->i_gid);
470 }
471 
472 /**
473  * capable_wrt_inode_uidgid - Check nsown_capable and uid and gid mapped
474  * @inode: The inode in question
475  * @cap: The capability in question
476  *
477  * Return true if the current task has the given capability targeted at
478  * its own user namespace and that the given inode's uid and gid are
479  * mapped into the current user namespace.
480  */
capable_wrt_inode_uidgid(const struct inode * inode,int cap)481 bool capable_wrt_inode_uidgid(const struct inode *inode, int cap)
482 {
483 	struct user_namespace *ns = current_user_ns();
484 
485 	return ns_capable(ns, cap) && privileged_wrt_inode_uidgid(ns, inode);
486 }
487 EXPORT_SYMBOL(capable_wrt_inode_uidgid);
488 
489 /**
490  * ptracer_capable - Determine if the ptracer holds CAP_SYS_PTRACE in the namespace
491  * @tsk: The task that may be ptraced
492  * @ns: The user namespace to search for CAP_SYS_PTRACE in
493  *
494  * Return true if the task that is ptracing the current task had CAP_SYS_PTRACE
495  * in the specified user namespace.
496  */
ptracer_capable(struct task_struct * tsk,struct user_namespace * ns)497 bool ptracer_capable(struct task_struct *tsk, struct user_namespace *ns)
498 {
499 	int ret = 0;  /* An absent tracer adds no restrictions */
500 	const struct cred *cred;
501 	rcu_read_lock();
502 	cred = rcu_dereference(tsk->ptracer_cred);
503 	if (cred)
504 		ret = security_capable_noaudit(cred, ns, CAP_SYS_PTRACE);
505 	rcu_read_unlock();
506 	return (ret == 0);
507 }
508