xref: /openbmc/linux/kernel/capability.c (revision 6672efbb)
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * linux/kernel/capability.c
4  *
5  * Copyright (C) 1997  Andrew Main <zefram@fysh.org>
6  *
7  * Integrated into 2.1.97+,  Andrew G. Morgan <morgan@kernel.org>
8  * 30 May 2002:	Cleanup, Robert M. Love <rml@tech9.net>
9  */
10 
11 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
12 
13 #include <linux/audit.h>
14 #include <linux/capability.h>
15 #include <linux/mm.h>
16 #include <linux/export.h>
17 #include <linux/security.h>
18 #include <linux/syscalls.h>
19 #include <linux/pid_namespace.h>
20 #include <linux/user_namespace.h>
21 #include <linux/uaccess.h>
22 
23 int file_caps_enabled = 1;
24 
file_caps_disable(char * str)25 static int __init file_caps_disable(char *str)
26 {
27 	file_caps_enabled = 0;
28 	return 1;
29 }
30 __setup("no_file_caps", file_caps_disable);
31 
32 #ifdef CONFIG_MULTIUSER
33 /*
34  * More recent versions of libcap are available from:
35  *
36  *   http://www.kernel.org/pub/linux/libs/security/linux-privs/
37  */
38 
warn_legacy_capability_use(void)39 static void warn_legacy_capability_use(void)
40 {
41 	char name[sizeof(current->comm)];
42 
43 	pr_info_once("warning: `%s' uses 32-bit capabilities (legacy support in use)\n",
44 		     get_task_comm(name, current));
45 }
46 
47 /*
48  * Version 2 capabilities worked fine, but the linux/capability.h file
49  * that accompanied their introduction encouraged their use without
50  * the necessary user-space source code changes. As such, we have
51  * created a version 3 with equivalent functionality to version 2, but
52  * with a header change to protect legacy source code from using
53  * version 2 when it wanted to use version 1. If your system has code
54  * that trips the following warning, it is using version 2 specific
55  * capabilities and may be doing so insecurely.
56  *
57  * The remedy is to either upgrade your version of libcap (to 2.10+,
58  * if the application is linked against it), or recompile your
59  * application with modern kernel headers and this warning will go
60  * away.
61  */
62 
warn_deprecated_v2(void)63 static void warn_deprecated_v2(void)
64 {
65 	char name[sizeof(current->comm)];
66 
67 	pr_info_once("warning: `%s' uses deprecated v2 capabilities in a way that may be insecure\n",
68 		     get_task_comm(name, current));
69 }
70 
71 /*
72  * Version check. Return the number of u32s in each capability flag
73  * array, or a negative value on error.
74  */
cap_validate_magic(cap_user_header_t header,unsigned * tocopy)75 static int cap_validate_magic(cap_user_header_t header, unsigned *tocopy)
76 {
77 	__u32 version;
78 
79 	if (get_user(version, &header->version))
80 		return -EFAULT;
81 
82 	switch (version) {
83 	case _LINUX_CAPABILITY_VERSION_1:
84 		warn_legacy_capability_use();
85 		*tocopy = _LINUX_CAPABILITY_U32S_1;
86 		break;
87 	case _LINUX_CAPABILITY_VERSION_2:
88 		warn_deprecated_v2();
89 		fallthrough;	/* v3 is otherwise equivalent to v2 */
90 	case _LINUX_CAPABILITY_VERSION_3:
91 		*tocopy = _LINUX_CAPABILITY_U32S_3;
92 		break;
93 	default:
94 		if (put_user((u32)_KERNEL_CAPABILITY_VERSION, &header->version))
95 			return -EFAULT;
96 		return -EINVAL;
97 	}
98 
99 	return 0;
100 }
101 
102 /*
103  * The only thing that can change the capabilities of the current
104  * process is the current process. As such, we can't be in this code
105  * at the same time as we are in the process of setting capabilities
106  * in this process. The net result is that we can limit our use of
107  * locks to when we are reading the caps of another process.
108  */
cap_get_target_pid(pid_t pid,kernel_cap_t * pEp,kernel_cap_t * pIp,kernel_cap_t * pPp)109 static inline int cap_get_target_pid(pid_t pid, kernel_cap_t *pEp,
110 				     kernel_cap_t *pIp, kernel_cap_t *pPp)
111 {
112 	int ret;
113 
114 	if (pid && (pid != task_pid_vnr(current))) {
115 		const struct task_struct *target;
116 
117 		rcu_read_lock();
118 
119 		target = find_task_by_vpid(pid);
120 		if (!target)
121 			ret = -ESRCH;
122 		else
123 			ret = security_capget(target, pEp, pIp, pPp);
124 
125 		rcu_read_unlock();
126 	} else
127 		ret = security_capget(current, pEp, pIp, pPp);
128 
129 	return ret;
130 }
131 
132 /**
133  * sys_capget - get the capabilities of a given process.
134  * @header: pointer to struct that contains capability version and
135  *	target pid data
136  * @dataptr: pointer to struct that contains the effective, permitted,
137  *	and inheritable capabilities that are returned
138  *
139  * Returns 0 on success and < 0 on error.
140  */
SYSCALL_DEFINE2(capget,cap_user_header_t,header,cap_user_data_t,dataptr)141 SYSCALL_DEFINE2(capget, cap_user_header_t, header, cap_user_data_t, dataptr)
142 {
143 	int ret = 0;
144 	pid_t pid;
145 	unsigned tocopy;
146 	kernel_cap_t pE, pI, pP;
147 	struct __user_cap_data_struct kdata[2];
148 
149 	ret = cap_validate_magic(header, &tocopy);
150 	if ((dataptr == NULL) || (ret != 0))
151 		return ((dataptr == NULL) && (ret == -EINVAL)) ? 0 : ret;
152 
153 	if (get_user(pid, &header->pid))
154 		return -EFAULT;
155 
156 	if (pid < 0)
157 		return -EINVAL;
158 
159 	ret = cap_get_target_pid(pid, &pE, &pI, &pP);
160 	if (ret)
161 		return ret;
162 
163 	/*
164 	 * Annoying legacy format with 64-bit capabilities exposed
165 	 * as two sets of 32-bit fields, so we need to split the
166 	 * capability values up.
167 	 */
168 	kdata[0].effective   = pE.val; kdata[1].effective   = pE.val >> 32;
169 	kdata[0].permitted   = pP.val; kdata[1].permitted   = pP.val >> 32;
170 	kdata[0].inheritable = pI.val; kdata[1].inheritable = pI.val >> 32;
171 
172 	/*
173 	 * Note, in the case, tocopy < _KERNEL_CAPABILITY_U32S,
174 	 * we silently drop the upper capabilities here. This
175 	 * has the effect of making older libcap
176 	 * implementations implicitly drop upper capability
177 	 * bits when they perform a: capget/modify/capset
178 	 * sequence.
179 	 *
180 	 * This behavior is considered fail-safe
181 	 * behavior. Upgrading the application to a newer
182 	 * version of libcap will enable access to the newer
183 	 * capabilities.
184 	 *
185 	 * An alternative would be to return an error here
186 	 * (-ERANGE), but that causes legacy applications to
187 	 * unexpectedly fail; the capget/modify/capset aborts
188 	 * before modification is attempted and the application
189 	 * fails.
190 	 */
191 	if (copy_to_user(dataptr, kdata, tocopy * sizeof(kdata[0])))
192 		return -EFAULT;
193 
194 	return 0;
195 }
196 
mk_kernel_cap(u32 low,u32 high)197 static kernel_cap_t mk_kernel_cap(u32 low, u32 high)
198 {
199 	return (kernel_cap_t) { (low | ((u64)high << 32)) & CAP_VALID_MASK };
200 }
201 
202 /**
203  * sys_capset - set capabilities for a process or (*) a group of processes
204  * @header: pointer to struct that contains capability version and
205  *	target pid data
206  * @data: pointer to struct that contains the effective, permitted,
207  *	and inheritable capabilities
208  *
209  * Set capabilities for the current process only.  The ability to any other
210  * process(es) has been deprecated and removed.
211  *
212  * The restrictions on setting capabilities are specified as:
213  *
214  * I: any raised capabilities must be a subset of the old permitted
215  * P: any raised capabilities must be a subset of the old permitted
216  * E: must be set to a subset of new permitted
217  *
218  * Returns 0 on success and < 0 on error.
219  */
SYSCALL_DEFINE2(capset,cap_user_header_t,header,const cap_user_data_t,data)220 SYSCALL_DEFINE2(capset, cap_user_header_t, header, const cap_user_data_t, data)
221 {
222 	struct __user_cap_data_struct kdata[2] = { { 0, }, };
223 	unsigned tocopy, copybytes;
224 	kernel_cap_t inheritable, permitted, effective;
225 	struct cred *new;
226 	int ret;
227 	pid_t pid;
228 
229 	ret = cap_validate_magic(header, &tocopy);
230 	if (ret != 0)
231 		return ret;
232 
233 	if (get_user(pid, &header->pid))
234 		return -EFAULT;
235 
236 	/* may only affect current now */
237 	if (pid != 0 && pid != task_pid_vnr(current))
238 		return -EPERM;
239 
240 	copybytes = tocopy * sizeof(struct __user_cap_data_struct);
241 	if (copybytes > sizeof(kdata))
242 		return -EFAULT;
243 
244 	if (copy_from_user(&kdata, data, copybytes))
245 		return -EFAULT;
246 
247 	effective   = mk_kernel_cap(kdata[0].effective,   kdata[1].effective);
248 	permitted   = mk_kernel_cap(kdata[0].permitted,   kdata[1].permitted);
249 	inheritable = mk_kernel_cap(kdata[0].inheritable, kdata[1].inheritable);
250 
251 	new = prepare_creds();
252 	if (!new)
253 		return -ENOMEM;
254 
255 	ret = security_capset(new, current_cred(),
256 			      &effective, &inheritable, &permitted);
257 	if (ret < 0)
258 		goto error;
259 
260 	audit_log_capset(new, current_cred());
261 
262 	return commit_creds(new);
263 
264 error:
265 	abort_creds(new);
266 	return ret;
267 }
268 
269 /**
270  * has_ns_capability - Does a task have a capability in a specific user ns
271  * @t: The task in question
272  * @ns: target user namespace
273  * @cap: The capability to be tested for
274  *
275  * Return true if the specified task has the given superior capability
276  * currently in effect to the specified user namespace, false if not.
277  *
278  * Note that this does not set PF_SUPERPRIV on the task.
279  */
has_ns_capability(struct task_struct * t,struct user_namespace * ns,int cap)280 bool has_ns_capability(struct task_struct *t,
281 		       struct user_namespace *ns, int cap)
282 {
283 	int ret;
284 
285 	rcu_read_lock();
286 	ret = security_capable(__task_cred(t), ns, cap, CAP_OPT_NONE);
287 	rcu_read_unlock();
288 
289 	return (ret == 0);
290 }
291 
292 /**
293  * has_capability - Does a task have a capability in init_user_ns
294  * @t: The task in question
295  * @cap: The capability to be tested for
296  *
297  * Return true if the specified task has the given superior capability
298  * currently in effect to the initial user namespace, false if not.
299  *
300  * Note that this does not set PF_SUPERPRIV on the task.
301  */
has_capability(struct task_struct * t,int cap)302 bool has_capability(struct task_struct *t, int cap)
303 {
304 	return has_ns_capability(t, &init_user_ns, cap);
305 }
306 EXPORT_SYMBOL(has_capability);
307 
308 /**
309  * has_ns_capability_noaudit - Does a task have a capability (unaudited)
310  * in a specific user ns.
311  * @t: The task in question
312  * @ns: target user namespace
313  * @cap: The capability to be tested for
314  *
315  * Return true if the specified task has the given superior capability
316  * currently in effect to the specified user namespace, false if not.
317  * Do not write an audit message for the check.
318  *
319  * Note that this does not set PF_SUPERPRIV on the task.
320  */
has_ns_capability_noaudit(struct task_struct * t,struct user_namespace * ns,int cap)321 bool has_ns_capability_noaudit(struct task_struct *t,
322 			       struct user_namespace *ns, int cap)
323 {
324 	int ret;
325 
326 	rcu_read_lock();
327 	ret = security_capable(__task_cred(t), ns, cap, CAP_OPT_NOAUDIT);
328 	rcu_read_unlock();
329 
330 	return (ret == 0);
331 }
332 
333 /**
334  * has_capability_noaudit - Does a task have a capability (unaudited) in the
335  * initial user ns
336  * @t: The task in question
337  * @cap: The capability to be tested for
338  *
339  * Return true if the specified task has the given superior capability
340  * currently in effect to init_user_ns, false if not.  Don't write an
341  * audit message for the check.
342  *
343  * Note that this does not set PF_SUPERPRIV on the task.
344  */
has_capability_noaudit(struct task_struct * t,int cap)345 bool has_capability_noaudit(struct task_struct *t, int cap)
346 {
347 	return has_ns_capability_noaudit(t, &init_user_ns, cap);
348 }
349 EXPORT_SYMBOL(has_capability_noaudit);
350 
ns_capable_common(struct user_namespace * ns,int cap,unsigned int opts)351 static bool ns_capable_common(struct user_namespace *ns,
352 			      int cap,
353 			      unsigned int opts)
354 {
355 	int capable;
356 
357 	if (unlikely(!cap_valid(cap))) {
358 		pr_crit("capable() called with invalid cap=%u\n", cap);
359 		BUG();
360 	}
361 
362 	capable = security_capable(current_cred(), ns, cap, opts);
363 	if (capable == 0) {
364 		current->flags |= PF_SUPERPRIV;
365 		return true;
366 	}
367 	return false;
368 }
369 
370 /**
371  * ns_capable - Determine if the current task has a superior capability in effect
372  * @ns:  The usernamespace we want the capability in
373  * @cap: The capability to be tested for
374  *
375  * Return true if the current task has the given superior capability currently
376  * available for use, false if not.
377  *
378  * This sets PF_SUPERPRIV on the task if the capability is available on the
379  * assumption that it's about to be used.
380  */
ns_capable(struct user_namespace * ns,int cap)381 bool ns_capable(struct user_namespace *ns, int cap)
382 {
383 	return ns_capable_common(ns, cap, CAP_OPT_NONE);
384 }
385 EXPORT_SYMBOL(ns_capable);
386 
387 /**
388  * ns_capable_noaudit - Determine if the current task has a superior capability
389  * (unaudited) in effect
390  * @ns:  The usernamespace we want the capability in
391  * @cap: The capability to be tested for
392  *
393  * Return true if the current task has the given superior capability currently
394  * available for use, false if not.
395  *
396  * This sets PF_SUPERPRIV on the task if the capability is available on the
397  * assumption that it's about to be used.
398  */
ns_capable_noaudit(struct user_namespace * ns,int cap)399 bool ns_capable_noaudit(struct user_namespace *ns, int cap)
400 {
401 	return ns_capable_common(ns, cap, CAP_OPT_NOAUDIT);
402 }
403 EXPORT_SYMBOL(ns_capable_noaudit);
404 
405 /**
406  * ns_capable_setid - Determine if the current task has a superior capability
407  * in effect, while signalling that this check is being done from within a
408  * setid or setgroups syscall.
409  * @ns:  The usernamespace we want the capability in
410  * @cap: The capability to be tested for
411  *
412  * Return true if the current task has the given superior capability currently
413  * available for use, false if not.
414  *
415  * This sets PF_SUPERPRIV on the task if the capability is available on the
416  * assumption that it's about to be used.
417  */
ns_capable_setid(struct user_namespace * ns,int cap)418 bool ns_capable_setid(struct user_namespace *ns, int cap)
419 {
420 	return ns_capable_common(ns, cap, CAP_OPT_INSETID);
421 }
422 EXPORT_SYMBOL(ns_capable_setid);
423 
424 /**
425  * capable - Determine if the current task has a superior capability in effect
426  * @cap: The capability to be tested for
427  *
428  * Return true if the current task has the given superior capability currently
429  * available for use, false if not.
430  *
431  * This sets PF_SUPERPRIV on the task if the capability is available on the
432  * assumption that it's about to be used.
433  */
capable(int cap)434 bool capable(int cap)
435 {
436 	return ns_capable(&init_user_ns, cap);
437 }
438 EXPORT_SYMBOL(capable);
439 #endif /* CONFIG_MULTIUSER */
440 
441 /**
442  * file_ns_capable - Determine if the file's opener had a capability in effect
443  * @file:  The file we want to check
444  * @ns:  The usernamespace we want the capability in
445  * @cap: The capability to be tested for
446  *
447  * Return true if task that opened the file had a capability in effect
448  * when the file was opened.
449  *
450  * This does not set PF_SUPERPRIV because the caller may not
451  * actually be privileged.
452  */
file_ns_capable(const struct file * file,struct user_namespace * ns,int cap)453 bool file_ns_capable(const struct file *file, struct user_namespace *ns,
454 		     int cap)
455 {
456 
457 	if (WARN_ON_ONCE(!cap_valid(cap)))
458 		return false;
459 
460 	if (security_capable(file->f_cred, ns, cap, CAP_OPT_NONE) == 0)
461 		return true;
462 
463 	return false;
464 }
465 EXPORT_SYMBOL(file_ns_capable);
466 
467 /**
468  * privileged_wrt_inode_uidgid - Do capabilities in the namespace work over the inode?
469  * @ns: The user namespace in question
470  * @idmap: idmap of the mount @inode was found from
471  * @inode: The inode in question
472  *
473  * Return true if the inode uid and gid are within the namespace.
474  */
privileged_wrt_inode_uidgid(struct user_namespace * ns,struct mnt_idmap * idmap,const struct inode * inode)475 bool privileged_wrt_inode_uidgid(struct user_namespace *ns,
476 				 struct mnt_idmap *idmap,
477 				 const struct inode *inode)
478 {
479 	return vfsuid_has_mapping(ns, i_uid_into_vfsuid(idmap, inode)) &&
480 	       vfsgid_has_mapping(ns, i_gid_into_vfsgid(idmap, inode));
481 }
482 
483 /**
484  * capable_wrt_inode_uidgid - Check nsown_capable and uid and gid mapped
485  * @idmap: idmap of the mount @inode was found from
486  * @inode: The inode in question
487  * @cap: The capability in question
488  *
489  * Return true if the current task has the given capability targeted at
490  * its own user namespace and that the given inode's uid and gid are
491  * mapped into the current user namespace.
492  */
capable_wrt_inode_uidgid(struct mnt_idmap * idmap,const struct inode * inode,int cap)493 bool capable_wrt_inode_uidgid(struct mnt_idmap *idmap,
494 			      const struct inode *inode, int cap)
495 {
496 	struct user_namespace *ns = current_user_ns();
497 
498 	return ns_capable(ns, cap) &&
499 	       privileged_wrt_inode_uidgid(ns, idmap, inode);
500 }
501 EXPORT_SYMBOL(capable_wrt_inode_uidgid);
502 
503 /**
504  * ptracer_capable - Determine if the ptracer holds CAP_SYS_PTRACE in the namespace
505  * @tsk: The task that may be ptraced
506  * @ns: The user namespace to search for CAP_SYS_PTRACE in
507  *
508  * Return true if the task that is ptracing the current task had CAP_SYS_PTRACE
509  * in the specified user namespace.
510  */
ptracer_capable(struct task_struct * tsk,struct user_namespace * ns)511 bool ptracer_capable(struct task_struct *tsk, struct user_namespace *ns)
512 {
513 	int ret = 0;  /* An absent tracer adds no restrictions */
514 	const struct cred *cred;
515 
516 	rcu_read_lock();
517 	cred = rcu_dereference(tsk->ptracer_cred);
518 	if (cred)
519 		ret = security_capable(cred, ns, CAP_SYS_PTRACE,
520 				       CAP_OPT_NOAUDIT);
521 	rcu_read_unlock();
522 	return (ret == 0);
523 }
524