1 /* Credentials management - see Documentation/security/credentials.rst
2  *
3  * Copyright (C) 2008 Red Hat, Inc. All Rights Reserved.
4  * Written by David Howells (dhowells@redhat.com)
5  *
6  * This program is free software; you can redistribute it and/or
7  * modify it under the terms of the GNU General Public Licence
8  * as published by the Free Software Foundation; either version
9  * 2 of the Licence, or (at your option) any later version.
10  */
11 
12 #ifndef _LINUX_CRED_H
13 #define _LINUX_CRED_H
14 
15 #include <linux/capability.h>
16 #include <linux/init.h>
17 #include <linux/key.h>
18 #include <linux/selinux.h>
19 #include <linux/atomic.h>
20 #include <linux/uidgid.h>
21 #include <linux/sched.h>
22 #include <linux/sched/user.h>
23 
24 struct cred;
25 struct inode;
26 
27 /*
28  * COW Supplementary groups list
29  */
30 struct group_info {
31 	atomic_t	usage;
32 	int		ngroups;
33 	kgid_t		gid[0];
34 } __randomize_layout;
35 
36 /**
37  * get_group_info - Get a reference to a group info structure
38  * @group_info: The group info to reference
39  *
40  * This gets a reference to a set of supplementary groups.
41  *
42  * If the caller is accessing a task's credentials, they must hold the RCU read
43  * lock when reading.
44  */
get_group_info(struct group_info * gi)45 static inline struct group_info *get_group_info(struct group_info *gi)
46 {
47 	atomic_inc(&gi->usage);
48 	return gi;
49 }
50 
51 /**
52  * put_group_info - Release a reference to a group info structure
53  * @group_info: The group info to release
54  */
55 #define put_group_info(group_info)			\
56 do {							\
57 	if (atomic_dec_and_test(&(group_info)->usage))	\
58 		groups_free(group_info);		\
59 } while (0)
60 
61 extern struct group_info init_groups;
62 #ifdef CONFIG_MULTIUSER
63 extern struct group_info *groups_alloc(int);
64 extern void groups_free(struct group_info *);
65 
66 extern int in_group_p(kgid_t);
67 extern int in_egroup_p(kgid_t);
68 extern int groups_search(const struct group_info *, kgid_t);
69 
70 extern int set_current_groups(struct group_info *);
71 extern void set_groups(struct cred *, struct group_info *);
72 extern bool may_setgroups(void);
73 extern void groups_sort(struct group_info *);
74 #else
groups_free(struct group_info * group_info)75 static inline void groups_free(struct group_info *group_info)
76 {
77 }
78 
in_group_p(kgid_t grp)79 static inline int in_group_p(kgid_t grp)
80 {
81         return 1;
82 }
in_egroup_p(kgid_t grp)83 static inline int in_egroup_p(kgid_t grp)
84 {
85         return 1;
86 }
groups_search(const struct group_info * group_info,kgid_t grp)87 static inline int groups_search(const struct group_info *group_info, kgid_t grp)
88 {
89 	return 1;
90 }
91 #endif
92 
93 /*
94  * The security context of a task
95  *
96  * The parts of the context break down into two categories:
97  *
98  *  (1) The objective context of a task.  These parts are used when some other
99  *	task is attempting to affect this one.
100  *
101  *  (2) The subjective context.  These details are used when the task is acting
102  *	upon another object, be that a file, a task, a key or whatever.
103  *
104  * Note that some members of this structure belong to both categories - the
105  * LSM security pointer for instance.
106  *
107  * A task has two security pointers.  task->real_cred points to the objective
108  * context that defines that task's actual details.  The objective part of this
109  * context is used whenever that task is acted upon.
110  *
111  * task->cred points to the subjective context that defines the details of how
112  * that task is going to act upon another object.  This may be overridden
113  * temporarily to point to another security context, but normally points to the
114  * same context as task->real_cred.
115  */
116 struct cred {
117 	atomic_t	usage;
118 #ifdef CONFIG_DEBUG_CREDENTIALS
119 	atomic_t	subscribers;	/* number of processes subscribed */
120 	void		*put_addr;
121 	unsigned	magic;
122 #define CRED_MAGIC	0x43736564
123 #define CRED_MAGIC_DEAD	0x44656144
124 #endif
125 	kuid_t		uid;		/* real UID of the task */
126 	kgid_t		gid;		/* real GID of the task */
127 	kuid_t		suid;		/* saved UID of the task */
128 	kgid_t		sgid;		/* saved GID of the task */
129 	kuid_t		euid;		/* effective UID of the task */
130 	kgid_t		egid;		/* effective GID of the task */
131 	kuid_t		fsuid;		/* UID for VFS ops */
132 	kgid_t		fsgid;		/* GID for VFS ops */
133 	unsigned	securebits;	/* SUID-less security management */
134 	kernel_cap_t	cap_inheritable; /* caps our children can inherit */
135 	kernel_cap_t	cap_permitted;	/* caps we're permitted */
136 	kernel_cap_t	cap_effective;	/* caps we can actually use */
137 	kernel_cap_t	cap_bset;	/* capability bounding set */
138 	kernel_cap_t	cap_ambient;	/* Ambient capability set */
139 #ifdef CONFIG_KEYS
140 	unsigned char	jit_keyring;	/* default keyring to attach requested
141 					 * keys to */
142 	struct key __rcu *session_keyring; /* keyring inherited over fork */
143 	struct key	*process_keyring; /* keyring private to this process */
144 	struct key	*thread_keyring; /* keyring private to this thread */
145 	struct key	*request_key_auth; /* assumed request_key authority */
146 #endif
147 #ifdef CONFIG_SECURITY
148 	void		*security;	/* subjective LSM security */
149 #endif
150 	struct user_struct *user;	/* real user ID subscription */
151 	struct user_namespace *user_ns; /* user_ns the caps and keyrings are relative to. */
152 	struct group_info *group_info;	/* supplementary groups for euid/fsgid */
153 	struct rcu_head	rcu;		/* RCU deletion hook */
154 } __randomize_layout;
155 
156 extern void __put_cred(struct cred *);
157 extern void exit_creds(struct task_struct *);
158 extern int copy_creds(struct task_struct *, unsigned long);
159 extern const struct cred *get_task_cred(struct task_struct *);
160 extern struct cred *cred_alloc_blank(void);
161 extern struct cred *prepare_creds(void);
162 extern struct cred *prepare_exec_creds(void);
163 extern int commit_creds(struct cred *);
164 extern void abort_creds(struct cred *);
165 extern const struct cred *override_creds(const struct cred *);
166 extern void revert_creds(const struct cred *);
167 extern struct cred *prepare_kernel_cred(struct task_struct *);
168 extern int change_create_files_as(struct cred *, struct inode *);
169 extern int set_security_override(struct cred *, u32);
170 extern int set_security_override_from_ctx(struct cred *, const char *);
171 extern int set_create_files_as(struct cred *, struct inode *);
172 extern void __init cred_init(void);
173 
174 /*
175  * check for validity of credentials
176  */
177 #ifdef CONFIG_DEBUG_CREDENTIALS
178 extern void __invalid_creds(const struct cred *, const char *, unsigned);
179 extern void __validate_process_creds(struct task_struct *,
180 				     const char *, unsigned);
181 
182 extern bool creds_are_invalid(const struct cred *cred);
183 
__validate_creds(const struct cred * cred,const char * file,unsigned line)184 static inline void __validate_creds(const struct cred *cred,
185 				    const char *file, unsigned line)
186 {
187 	if (unlikely(creds_are_invalid(cred)))
188 		__invalid_creds(cred, file, line);
189 }
190 
191 #define validate_creds(cred)				\
192 do {							\
193 	__validate_creds((cred), __FILE__, __LINE__);	\
194 } while(0)
195 
196 #define validate_process_creds()				\
197 do {								\
198 	__validate_process_creds(current, __FILE__, __LINE__);	\
199 } while(0)
200 
201 extern void validate_creds_for_do_exit(struct task_struct *);
202 #else
validate_creds(const struct cred * cred)203 static inline void validate_creds(const struct cred *cred)
204 {
205 }
validate_creds_for_do_exit(struct task_struct * tsk)206 static inline void validate_creds_for_do_exit(struct task_struct *tsk)
207 {
208 }
validate_process_creds(void)209 static inline void validate_process_creds(void)
210 {
211 }
212 #endif
213 
cap_ambient_invariant_ok(const struct cred * cred)214 static inline bool cap_ambient_invariant_ok(const struct cred *cred)
215 {
216 	return cap_issubset(cred->cap_ambient,
217 			    cap_intersect(cred->cap_permitted,
218 					  cred->cap_inheritable));
219 }
220 
221 /**
222  * get_new_cred - Get a reference on a new set of credentials
223  * @cred: The new credentials to reference
224  *
225  * Get a reference on the specified set of new credentials.  The caller must
226  * release the reference.
227  */
get_new_cred(struct cred * cred)228 static inline struct cred *get_new_cred(struct cred *cred)
229 {
230 	atomic_inc(&cred->usage);
231 	return cred;
232 }
233 
234 /**
235  * get_cred - Get a reference on a set of credentials
236  * @cred: The credentials to reference
237  *
238  * Get a reference on the specified set of credentials.  The caller must
239  * release the reference.
240  *
241  * This is used to deal with a committed set of credentials.  Although the
242  * pointer is const, this will temporarily discard the const and increment the
243  * usage count.  The purpose of this is to attempt to catch at compile time the
244  * accidental alteration of a set of credentials that should be considered
245  * immutable.
246  */
get_cred(const struct cred * cred)247 static inline const struct cred *get_cred(const struct cred *cred)
248 {
249 	struct cred *nonconst_cred = (struct cred *) cred;
250 	validate_creds(cred);
251 	return get_new_cred(nonconst_cred);
252 }
253 
254 /**
255  * put_cred - Release a reference to a set of credentials
256  * @cred: The credentials to release
257  *
258  * Release a reference to a set of credentials, deleting them when the last ref
259  * is released.
260  *
261  * This takes a const pointer to a set of credentials because the credentials
262  * on task_struct are attached by const pointers to prevent accidental
263  * alteration of otherwise immutable credential sets.
264  */
put_cred(const struct cred * _cred)265 static inline void put_cred(const struct cred *_cred)
266 {
267 	struct cred *cred = (struct cred *) _cred;
268 
269 	validate_creds(cred);
270 	if (atomic_dec_and_test(&(cred)->usage))
271 		__put_cred(cred);
272 }
273 
274 /**
275  * current_cred - Access the current task's subjective credentials
276  *
277  * Access the subjective credentials of the current task.  RCU-safe,
278  * since nobody else can modify it.
279  */
280 #define current_cred() \
281 	rcu_dereference_protected(current->cred, 1)
282 
283 /**
284  * current_real_cred - Access the current task's objective credentials
285  *
286  * Access the objective credentials of the current task.  RCU-safe,
287  * since nobody else can modify it.
288  */
289 #define current_real_cred() \
290 	rcu_dereference_protected(current->real_cred, 1)
291 
292 /**
293  * __task_cred - Access a task's objective credentials
294  * @task: The task to query
295  *
296  * Access the objective credentials of a task.  The caller must hold the RCU
297  * readlock.
298  *
299  * The result of this function should not be passed directly to get_cred();
300  * rather get_task_cred() should be used instead.
301  */
302 #define __task_cred(task)	\
303 	rcu_dereference((task)->real_cred)
304 
305 /**
306  * get_current_cred - Get the current task's subjective credentials
307  *
308  * Get the subjective credentials of the current task, pinning them so that
309  * they can't go away.  Accessing the current task's credentials directly is
310  * not permitted.
311  */
312 #define get_current_cred()				\
313 	(get_cred(current_cred()))
314 
315 /**
316  * get_current_user - Get the current task's user_struct
317  *
318  * Get the user record of the current task, pinning it so that it can't go
319  * away.
320  */
321 #define get_current_user()				\
322 ({							\
323 	struct user_struct *__u;			\
324 	const struct cred *__cred;			\
325 	__cred = current_cred();			\
326 	__u = get_uid(__cred->user);			\
327 	__u;						\
328 })
329 
330 /**
331  * get_current_groups - Get the current task's supplementary group list
332  *
333  * Get the supplementary group list of the current task, pinning it so that it
334  * can't go away.
335  */
336 #define get_current_groups()				\
337 ({							\
338 	struct group_info *__groups;			\
339 	const struct cred *__cred;			\
340 	__cred = current_cred();			\
341 	__groups = get_group_info(__cred->group_info);	\
342 	__groups;					\
343 })
344 
345 #define task_cred_xxx(task, xxx)			\
346 ({							\
347 	__typeof__(((struct cred *)NULL)->xxx) ___val;	\
348 	rcu_read_lock();				\
349 	___val = __task_cred((task))->xxx;		\
350 	rcu_read_unlock();				\
351 	___val;						\
352 })
353 
354 #define task_uid(task)		(task_cred_xxx((task), uid))
355 #define task_euid(task)		(task_cred_xxx((task), euid))
356 
357 #define current_cred_xxx(xxx)			\
358 ({						\
359 	current_cred()->xxx;			\
360 })
361 
362 #define current_uid()		(current_cred_xxx(uid))
363 #define current_gid()		(current_cred_xxx(gid))
364 #define current_euid()		(current_cred_xxx(euid))
365 #define current_egid()		(current_cred_xxx(egid))
366 #define current_suid()		(current_cred_xxx(suid))
367 #define current_sgid()		(current_cred_xxx(sgid))
368 #define current_fsuid() 	(current_cred_xxx(fsuid))
369 #define current_fsgid() 	(current_cred_xxx(fsgid))
370 #define current_cap()		(current_cred_xxx(cap_effective))
371 #define current_user()		(current_cred_xxx(user))
372 #define current_security()	(current_cred_xxx(security))
373 
374 extern struct user_namespace init_user_ns;
375 #ifdef CONFIG_USER_NS
376 #define current_user_ns()	(current_cred_xxx(user_ns))
377 #else
current_user_ns(void)378 static inline struct user_namespace *current_user_ns(void)
379 {
380 	return &init_user_ns;
381 }
382 #endif
383 
384 
385 #define current_uid_gid(_uid, _gid)		\
386 do {						\
387 	const struct cred *__cred;		\
388 	__cred = current_cred();		\
389 	*(_uid) = __cred->uid;			\
390 	*(_gid) = __cred->gid;			\
391 } while(0)
392 
393 #define current_euid_egid(_euid, _egid)		\
394 do {						\
395 	const struct cred *__cred;		\
396 	__cred = current_cred();		\
397 	*(_euid) = __cred->euid;		\
398 	*(_egid) = __cred->egid;		\
399 } while(0)
400 
401 #define current_fsuid_fsgid(_fsuid, _fsgid)	\
402 do {						\
403 	const struct cred *__cred;		\
404 	__cred = current_cred();		\
405 	*(_fsuid) = __cred->fsuid;		\
406 	*(_fsgid) = __cred->fsgid;		\
407 } while(0)
408 
409 #endif /* _LINUX_CRED_H */
410