1 /*
2  * linux/fs/posix_acl.c
3  *
4  *  Copyright (C) 2002 by Andreas Gruenbacher <a.gruenbacher@computer.org>
5  *
6  *  Fixes from William Schumacher incorporated on 15 March 2001.
7  *     (Reported by Charles Bertsch, <CBertsch@microtest.com>).
8  */
9 
10 /*
11  *  This file contains generic functions for manipulating
12  *  POSIX 1003.1e draft standard 17 ACLs.
13  */
14 
15 #include <linux/kernel.h>
16 #include <linux/slab.h>
17 #include <asm/atomic.h>
18 #include <linux/fs.h>
19 #include <linux/sched.h>
20 #include <linux/posix_acl.h>
21 #include <linux/module.h>
22 
23 #include <linux/errno.h>
24 
25 EXPORT_SYMBOL(posix_acl_init);
26 EXPORT_SYMBOL(posix_acl_alloc);
27 EXPORT_SYMBOL(posix_acl_clone);
28 EXPORT_SYMBOL(posix_acl_valid);
29 EXPORT_SYMBOL(posix_acl_equiv_mode);
30 EXPORT_SYMBOL(posix_acl_from_mode);
31 EXPORT_SYMBOL(posix_acl_create_masq);
32 EXPORT_SYMBOL(posix_acl_chmod_masq);
33 EXPORT_SYMBOL(posix_acl_permission);
34 
35 /*
36  * Init a fresh posix_acl
37  */
38 void
posix_acl_init(struct posix_acl * acl,int count)39 posix_acl_init(struct posix_acl *acl, int count)
40 {
41 	atomic_set(&acl->a_refcount, 1);
42 	acl->a_count = count;
43 }
44 
45 /*
46  * Allocate a new ACL with the specified number of entries.
47  */
48 struct posix_acl *
posix_acl_alloc(int count,gfp_t flags)49 posix_acl_alloc(int count, gfp_t flags)
50 {
51 	const size_t size = sizeof(struct posix_acl) +
52 	                    count * sizeof(struct posix_acl_entry);
53 	struct posix_acl *acl = kmalloc(size, flags);
54 	if (acl)
55 		posix_acl_init(acl, count);
56 	return acl;
57 }
58 
59 /*
60  * Clone an ACL.
61  */
62 struct posix_acl *
posix_acl_clone(const struct posix_acl * acl,gfp_t flags)63 posix_acl_clone(const struct posix_acl *acl, gfp_t flags)
64 {
65 	struct posix_acl *clone = NULL;
66 
67 	if (acl) {
68 		int size = sizeof(struct posix_acl) + acl->a_count *
69 		           sizeof(struct posix_acl_entry);
70 		clone = kmemdup(acl, size, flags);
71 		if (clone)
72 			atomic_set(&clone->a_refcount, 1);
73 	}
74 	return clone;
75 }
76 
77 /*
78  * Check if an acl is valid. Returns 0 if it is, or -E... otherwise.
79  */
80 int
posix_acl_valid(const struct posix_acl * acl)81 posix_acl_valid(const struct posix_acl *acl)
82 {
83 	const struct posix_acl_entry *pa, *pe;
84 	int state = ACL_USER_OBJ;
85 	unsigned int id = 0;  /* keep gcc happy */
86 	int needs_mask = 0;
87 
88 	FOREACH_ACL_ENTRY(pa, acl, pe) {
89 		if (pa->e_perm & ~(ACL_READ|ACL_WRITE|ACL_EXECUTE))
90 			return -EINVAL;
91 		switch (pa->e_tag) {
92 			case ACL_USER_OBJ:
93 				if (state == ACL_USER_OBJ) {
94 					id = 0;
95 					state = ACL_USER;
96 					break;
97 				}
98 				return -EINVAL;
99 
100 			case ACL_USER:
101 				if (state != ACL_USER)
102 					return -EINVAL;
103 				if (pa->e_id == ACL_UNDEFINED_ID ||
104 				    pa->e_id < id)
105 					return -EINVAL;
106 				id = pa->e_id + 1;
107 				needs_mask = 1;
108 				break;
109 
110 			case ACL_GROUP_OBJ:
111 				if (state == ACL_USER) {
112 					id = 0;
113 					state = ACL_GROUP;
114 					break;
115 				}
116 				return -EINVAL;
117 
118 			case ACL_GROUP:
119 				if (state != ACL_GROUP)
120 					return -EINVAL;
121 				if (pa->e_id == ACL_UNDEFINED_ID ||
122 				    pa->e_id < id)
123 					return -EINVAL;
124 				id = pa->e_id + 1;
125 				needs_mask = 1;
126 				break;
127 
128 			case ACL_MASK:
129 				if (state != ACL_GROUP)
130 					return -EINVAL;
131 				state = ACL_OTHER;
132 				break;
133 
134 			case ACL_OTHER:
135 				if (state == ACL_OTHER ||
136 				    (state == ACL_GROUP && !needs_mask)) {
137 					state = 0;
138 					break;
139 				}
140 				return -EINVAL;
141 
142 			default:
143 				return -EINVAL;
144 		}
145 	}
146 	if (state == 0)
147 		return 0;
148 	return -EINVAL;
149 }
150 
151 /*
152  * Returns 0 if the acl can be exactly represented in the traditional
153  * file mode permission bits, or else 1. Returns -E... on error.
154  */
155 int
posix_acl_equiv_mode(const struct posix_acl * acl,mode_t * mode_p)156 posix_acl_equiv_mode(const struct posix_acl *acl, mode_t *mode_p)
157 {
158 	const struct posix_acl_entry *pa, *pe;
159 	mode_t mode = 0;
160 	int not_equiv = 0;
161 
162 	FOREACH_ACL_ENTRY(pa, acl, pe) {
163 		switch (pa->e_tag) {
164 			case ACL_USER_OBJ:
165 				mode |= (pa->e_perm & S_IRWXO) << 6;
166 				break;
167 			case ACL_GROUP_OBJ:
168 				mode |= (pa->e_perm & S_IRWXO) << 3;
169 				break;
170 			case ACL_OTHER:
171 				mode |= pa->e_perm & S_IRWXO;
172 				break;
173 			case ACL_MASK:
174 				mode = (mode & ~S_IRWXG) |
175 				       ((pa->e_perm & S_IRWXO) << 3);
176 				not_equiv = 1;
177 				break;
178 			case ACL_USER:
179 			case ACL_GROUP:
180 				not_equiv = 1;
181 				break;
182 			default:
183 				return -EINVAL;
184 		}
185 	}
186         if (mode_p)
187                 *mode_p = (*mode_p & ~S_IRWXUGO) | mode;
188         return not_equiv;
189 }
190 
191 /*
192  * Create an ACL representing the file mode permission bits of an inode.
193  */
194 struct posix_acl *
posix_acl_from_mode(mode_t mode,gfp_t flags)195 posix_acl_from_mode(mode_t mode, gfp_t flags)
196 {
197 	struct posix_acl *acl = posix_acl_alloc(3, flags);
198 	if (!acl)
199 		return ERR_PTR(-ENOMEM);
200 
201 	acl->a_entries[0].e_tag  = ACL_USER_OBJ;
202 	acl->a_entries[0].e_id   = ACL_UNDEFINED_ID;
203 	acl->a_entries[0].e_perm = (mode & S_IRWXU) >> 6;
204 
205 	acl->a_entries[1].e_tag  = ACL_GROUP_OBJ;
206 	acl->a_entries[1].e_id   = ACL_UNDEFINED_ID;
207 	acl->a_entries[1].e_perm = (mode & S_IRWXG) >> 3;
208 
209 	acl->a_entries[2].e_tag  = ACL_OTHER;
210 	acl->a_entries[2].e_id   = ACL_UNDEFINED_ID;
211 	acl->a_entries[2].e_perm = (mode & S_IRWXO);
212 	return acl;
213 }
214 
215 /*
216  * Return 0 if current is granted want access to the inode
217  * by the acl. Returns -E... otherwise.
218  */
219 int
posix_acl_permission(struct inode * inode,const struct posix_acl * acl,int want)220 posix_acl_permission(struct inode *inode, const struct posix_acl *acl, int want)
221 {
222 	const struct posix_acl_entry *pa, *pe, *mask_obj;
223 	int found = 0;
224 
225 	FOREACH_ACL_ENTRY(pa, acl, pe) {
226                 switch(pa->e_tag) {
227                         case ACL_USER_OBJ:
228 				/* (May have been checked already) */
229 				if (inode->i_uid == current_fsuid())
230                                         goto check_perm;
231                                 break;
232                         case ACL_USER:
233 				if (pa->e_id == current_fsuid())
234                                         goto mask;
235 				break;
236                         case ACL_GROUP_OBJ:
237                                 if (in_group_p(inode->i_gid)) {
238 					found = 1;
239 					if ((pa->e_perm & want) == want)
240 						goto mask;
241                                 }
242 				break;
243                         case ACL_GROUP:
244                                 if (in_group_p(pa->e_id)) {
245 					found = 1;
246 					if ((pa->e_perm & want) == want)
247 						goto mask;
248                                 }
249                                 break;
250                         case ACL_MASK:
251                                 break;
252                         case ACL_OTHER:
253 				if (found)
254 					return -EACCES;
255 				else
256 					goto check_perm;
257 			default:
258 				return -EIO;
259                 }
260         }
261 	return -EIO;
262 
263 mask:
264 	for (mask_obj = pa+1; mask_obj != pe; mask_obj++) {
265 		if (mask_obj->e_tag == ACL_MASK) {
266 			if ((pa->e_perm & mask_obj->e_perm & want) == want)
267 				return 0;
268 			return -EACCES;
269 		}
270 	}
271 
272 check_perm:
273 	if ((pa->e_perm & want) == want)
274 		return 0;
275 	return -EACCES;
276 }
277 
278 /*
279  * Modify acl when creating a new inode. The caller must ensure the acl is
280  * only referenced once.
281  *
282  * mode_p initially must contain the mode parameter to the open() / creat()
283  * system calls. All permissions that are not granted by the acl are removed.
284  * The permissions in the acl are changed to reflect the mode_p parameter.
285  */
286 int
posix_acl_create_masq(struct posix_acl * acl,mode_t * mode_p)287 posix_acl_create_masq(struct posix_acl *acl, mode_t *mode_p)
288 {
289 	struct posix_acl_entry *pa, *pe;
290 	struct posix_acl_entry *group_obj = NULL, *mask_obj = NULL;
291 	mode_t mode = *mode_p;
292 	int not_equiv = 0;
293 
294 	/* assert(atomic_read(acl->a_refcount) == 1); */
295 
296 	FOREACH_ACL_ENTRY(pa, acl, pe) {
297                 switch(pa->e_tag) {
298                         case ACL_USER_OBJ:
299 				pa->e_perm &= (mode >> 6) | ~S_IRWXO;
300 				mode &= (pa->e_perm << 6) | ~S_IRWXU;
301 				break;
302 
303 			case ACL_USER:
304 			case ACL_GROUP:
305 				not_equiv = 1;
306 				break;
307 
308                         case ACL_GROUP_OBJ:
309 				group_obj = pa;
310                                 break;
311 
312                         case ACL_OTHER:
313 				pa->e_perm &= mode | ~S_IRWXO;
314 				mode &= pa->e_perm | ~S_IRWXO;
315                                 break;
316 
317                         case ACL_MASK:
318 				mask_obj = pa;
319 				not_equiv = 1;
320                                 break;
321 
322 			default:
323 				return -EIO;
324                 }
325         }
326 
327 	if (mask_obj) {
328 		mask_obj->e_perm &= (mode >> 3) | ~S_IRWXO;
329 		mode &= (mask_obj->e_perm << 3) | ~S_IRWXG;
330 	} else {
331 		if (!group_obj)
332 			return -EIO;
333 		group_obj->e_perm &= (mode >> 3) | ~S_IRWXO;
334 		mode &= (group_obj->e_perm << 3) | ~S_IRWXG;
335 	}
336 
337 	*mode_p = (*mode_p & ~S_IRWXUGO) | mode;
338         return not_equiv;
339 }
340 
341 /*
342  * Modify the ACL for the chmod syscall.
343  */
344 int
posix_acl_chmod_masq(struct posix_acl * acl,mode_t mode)345 posix_acl_chmod_masq(struct posix_acl *acl, mode_t mode)
346 {
347 	struct posix_acl_entry *group_obj = NULL, *mask_obj = NULL;
348 	struct posix_acl_entry *pa, *pe;
349 
350 	/* assert(atomic_read(acl->a_refcount) == 1); */
351 
352 	FOREACH_ACL_ENTRY(pa, acl, pe) {
353 		switch(pa->e_tag) {
354 			case ACL_USER_OBJ:
355 				pa->e_perm = (mode & S_IRWXU) >> 6;
356 				break;
357 
358 			case ACL_USER:
359 			case ACL_GROUP:
360 				break;
361 
362 			case ACL_GROUP_OBJ:
363 				group_obj = pa;
364 				break;
365 
366 			case ACL_MASK:
367 				mask_obj = pa;
368 				break;
369 
370 			case ACL_OTHER:
371 				pa->e_perm = (mode & S_IRWXO);
372 				break;
373 
374 			default:
375 				return -EIO;
376 		}
377 	}
378 
379 	if (mask_obj) {
380 		mask_obj->e_perm = (mode & S_IRWXG) >> 3;
381 	} else {
382 		if (!group_obj)
383 			return -EIO;
384 		group_obj->e_perm = (mode & S_IRWXG) >> 3;
385 	}
386 
387 	return 0;
388 }
389