xref: /linux/security/apparmor/file.c (revision 827634added7f38b7d724cab1dccdb2b004c13c3)
1 /*
2  * AppArmor security module
3  *
4  * This file contains AppArmor mediation of files
5  *
6  * Copyright (C) 1998-2008 Novell/SUSE
7  * Copyright 2009-2010 Canonical Ltd.
8  *
9  * This program is free software; you can redistribute it and/or
10  * modify it under the terms of the GNU General Public License as
11  * published by the Free Software Foundation, version 2 of the
12  * License.
13  */
14 
15 #include "include/apparmor.h"
16 #include "include/audit.h"
17 #include "include/file.h"
18 #include "include/match.h"
19 #include "include/path.h"
20 #include "include/policy.h"
21 
22 struct file_perms nullperms;
23 
24 
25 /**
26  * audit_file_mask - convert mask to permission string
27  * @buffer: buffer to write string to (NOT NULL)
28  * @mask: permission mask to convert
29  */
30 static void audit_file_mask(struct audit_buffer *ab, u32 mask)
31 {
32 	char str[10];
33 
34 	char *m = str;
35 
36 	if (mask & AA_EXEC_MMAP)
37 		*m++ = 'm';
38 	if (mask & (MAY_READ | AA_MAY_META_READ))
39 		*m++ = 'r';
40 	if (mask & (MAY_WRITE | AA_MAY_META_WRITE | AA_MAY_CHMOD |
41 		    AA_MAY_CHOWN))
42 		*m++ = 'w';
43 	else if (mask & MAY_APPEND)
44 		*m++ = 'a';
45 	if (mask & AA_MAY_CREATE)
46 		*m++ = 'c';
47 	if (mask & AA_MAY_DELETE)
48 		*m++ = 'd';
49 	if (mask & AA_MAY_LINK)
50 		*m++ = 'l';
51 	if (mask & AA_MAY_LOCK)
52 		*m++ = 'k';
53 	if (mask & MAY_EXEC)
54 		*m++ = 'x';
55 	*m = '\0';
56 
57 	audit_log_string(ab, str);
58 }
59 
60 /**
61  * file_audit_cb - call back for file specific audit fields
62  * @ab: audit_buffer  (NOT NULL)
63  * @va: audit struct to audit values of  (NOT NULL)
64  */
65 static void file_audit_cb(struct audit_buffer *ab, void *va)
66 {
67 	struct common_audit_data *sa = va;
68 	kuid_t fsuid = current_fsuid();
69 
70 	if (sa->aad->fs.request & AA_AUDIT_FILE_MASK) {
71 		audit_log_format(ab, " requested_mask=");
72 		audit_file_mask(ab, sa->aad->fs.request);
73 	}
74 	if (sa->aad->fs.denied & AA_AUDIT_FILE_MASK) {
75 		audit_log_format(ab, " denied_mask=");
76 		audit_file_mask(ab, sa->aad->fs.denied);
77 	}
78 	if (sa->aad->fs.request & AA_AUDIT_FILE_MASK) {
79 		audit_log_format(ab, " fsuid=%d",
80 				 from_kuid(&init_user_ns, fsuid));
81 		audit_log_format(ab, " ouid=%d",
82 				 from_kuid(&init_user_ns, sa->aad->fs.ouid));
83 	}
84 
85 	if (sa->aad->fs.target) {
86 		audit_log_format(ab, " target=");
87 		audit_log_untrustedstring(ab, sa->aad->fs.target);
88 	}
89 }
90 
91 /**
92  * aa_audit_file - handle the auditing of file operations
93  * @profile: the profile being enforced  (NOT NULL)
94  * @perms: the permissions computed for the request (NOT NULL)
95  * @gfp: allocation flags
96  * @op: operation being mediated
97  * @request: permissions requested
98  * @name: name of object being mediated (MAYBE NULL)
99  * @target: name of target (MAYBE NULL)
100  * @ouid: object uid
101  * @info: extra information message (MAYBE NULL)
102  * @error: 0 if operation allowed else failure error code
103  *
104  * Returns: %0 or error on failure
105  */
106 int aa_audit_file(struct aa_profile *profile, struct file_perms *perms,
107 		  gfp_t gfp, int op, u32 request, const char *name,
108 		  const char *target, kuid_t ouid, const char *info, int error)
109 {
110 	int type = AUDIT_APPARMOR_AUTO;
111 	struct common_audit_data sa;
112 	struct apparmor_audit_data aad = {0,};
113 	sa.type = LSM_AUDIT_DATA_NONE;
114 	sa.aad = &aad;
115 	aad.op = op,
116 	aad.fs.request = request;
117 	aad.name = name;
118 	aad.fs.target = target;
119 	aad.fs.ouid = ouid;
120 	aad.info = info;
121 	aad.error = error;
122 
123 	if (likely(!sa.aad->error)) {
124 		u32 mask = perms->audit;
125 
126 		if (unlikely(AUDIT_MODE(profile) == AUDIT_ALL))
127 			mask = 0xffff;
128 
129 		/* mask off perms that are not being force audited */
130 		sa.aad->fs.request &= mask;
131 
132 		if (likely(!sa.aad->fs.request))
133 			return 0;
134 		type = AUDIT_APPARMOR_AUDIT;
135 	} else {
136 		/* only report permissions that were denied */
137 		sa.aad->fs.request = sa.aad->fs.request & ~perms->allow;
138 
139 		if (sa.aad->fs.request & perms->kill)
140 			type = AUDIT_APPARMOR_KILL;
141 
142 		/* quiet known rejects, assumes quiet and kill do not overlap */
143 		if ((sa.aad->fs.request & perms->quiet) &&
144 		    AUDIT_MODE(profile) != AUDIT_NOQUIET &&
145 		    AUDIT_MODE(profile) != AUDIT_ALL)
146 			sa.aad->fs.request &= ~perms->quiet;
147 
148 		if (!sa.aad->fs.request)
149 			return COMPLAIN_MODE(profile) ? 0 : sa.aad->error;
150 	}
151 
152 	sa.aad->fs.denied = sa.aad->fs.request & ~perms->allow;
153 	return aa_audit(type, profile, gfp, &sa, file_audit_cb);
154 }
155 
156 /**
157  * map_old_perms - map old file perms layout to the new layout
158  * @old: permission set in old mapping
159  *
160  * Returns: new permission mapping
161  */
162 static u32 map_old_perms(u32 old)
163 {
164 	u32 new = old & 0xf;
165 	if (old & MAY_READ)
166 		new |= AA_MAY_META_READ;
167 	if (old & MAY_WRITE)
168 		new |= AA_MAY_META_WRITE | AA_MAY_CREATE | AA_MAY_DELETE |
169 			AA_MAY_CHMOD | AA_MAY_CHOWN;
170 	if (old & 0x10)
171 		new |= AA_MAY_LINK;
172 	/* the old mapping lock and link_subset flags where overlaid
173 	 * and use was determined by part of a pair that they were in
174 	 */
175 	if (old & 0x20)
176 		new |= AA_MAY_LOCK | AA_LINK_SUBSET;
177 	if (old & 0x40)	/* AA_EXEC_MMAP */
178 		new |= AA_EXEC_MMAP;
179 
180 	return new;
181 }
182 
183 /**
184  * compute_perms - convert dfa compressed perms to internal perms
185  * @dfa: dfa to compute perms for   (NOT NULL)
186  * @state: state in dfa
187  * @cond:  conditions to consider  (NOT NULL)
188  *
189  * TODO: convert from dfa + state to permission entry, do computation conversion
190  *       at load time.
191  *
192  * Returns: computed permission set
193  */
194 static struct file_perms compute_perms(struct aa_dfa *dfa, unsigned int state,
195 				       struct path_cond *cond)
196 {
197 	struct file_perms perms;
198 
199 	/* FIXME: change over to new dfa format
200 	 * currently file perms are encoded in the dfa, new format
201 	 * splits the permissions from the dfa.  This mapping can be
202 	 * done at profile load
203 	 */
204 	perms.kill = 0;
205 
206 	if (uid_eq(current_fsuid(), cond->uid)) {
207 		perms.allow = map_old_perms(dfa_user_allow(dfa, state));
208 		perms.audit = map_old_perms(dfa_user_audit(dfa, state));
209 		perms.quiet = map_old_perms(dfa_user_quiet(dfa, state));
210 		perms.xindex = dfa_user_xindex(dfa, state);
211 	} else {
212 		perms.allow = map_old_perms(dfa_other_allow(dfa, state));
213 		perms.audit = map_old_perms(dfa_other_audit(dfa, state));
214 		perms.quiet = map_old_perms(dfa_other_quiet(dfa, state));
215 		perms.xindex = dfa_other_xindex(dfa, state);
216 	}
217 	perms.allow |= AA_MAY_META_READ;
218 
219 	/* change_profile wasn't determined by ownership in old mapping */
220 	if (ACCEPT_TABLE(dfa)[state] & 0x80000000)
221 		perms.allow |= AA_MAY_CHANGE_PROFILE;
222 	if (ACCEPT_TABLE(dfa)[state] & 0x40000000)
223 		perms.allow |= AA_MAY_ONEXEC;
224 
225 	return perms;
226 }
227 
228 /**
229  * aa_str_perms - find permission that match @name
230  * @dfa: to match against  (MAYBE NULL)
231  * @state: state to start matching in
232  * @name: string to match against dfa  (NOT NULL)
233  * @cond: conditions to consider for permission set computation  (NOT NULL)
234  * @perms: Returns - the permissions found when matching @name
235  *
236  * Returns: the final state in @dfa when beginning @start and walking @name
237  */
238 unsigned int aa_str_perms(struct aa_dfa *dfa, unsigned int start,
239 			  const char *name, struct path_cond *cond,
240 			  struct file_perms *perms)
241 {
242 	unsigned int state;
243 	if (!dfa) {
244 		*perms = nullperms;
245 		return DFA_NOMATCH;
246 	}
247 
248 	state = aa_dfa_match(dfa, start, name);
249 	*perms = compute_perms(dfa, state, cond);
250 
251 	return state;
252 }
253 
254 /**
255  * is_deleted - test if a file has been completely unlinked
256  * @dentry: dentry of file to test for deletion  (NOT NULL)
257  *
258  * Returns: %1 if deleted else %0
259  */
260 static inline bool is_deleted(struct dentry *dentry)
261 {
262 	if (d_unlinked(dentry) && d_backing_inode(dentry)->i_nlink == 0)
263 		return 1;
264 	return 0;
265 }
266 
267 /**
268  * aa_path_perm - do permissions check & audit for @path
269  * @op: operation being checked
270  * @profile: profile being enforced  (NOT NULL)
271  * @path: path to check permissions of  (NOT NULL)
272  * @flags: any additional path flags beyond what the profile specifies
273  * @request: requested permissions
274  * @cond: conditional info for this request  (NOT NULL)
275  *
276  * Returns: %0 else error if access denied or other error
277  */
278 int aa_path_perm(int op, struct aa_profile *profile, struct path *path,
279 		 int flags, u32 request, struct path_cond *cond)
280 {
281 	char *buffer = NULL;
282 	struct file_perms perms = {};
283 	const char *name, *info = NULL;
284 	int error;
285 
286 	flags |= profile->path_flags | (S_ISDIR(cond->mode) ? PATH_IS_DIR : 0);
287 	error = aa_path_name(path, flags, &buffer, &name, &info);
288 	if (error) {
289 		if (error == -ENOENT && is_deleted(path->dentry)) {
290 			/* Access to open files that are deleted are
291 			 * give a pass (implicit delegation)
292 			 */
293 			error = 0;
294 			info = NULL;
295 			perms.allow = request;
296 		}
297 	} else {
298 		aa_str_perms(profile->file.dfa, profile->file.start, name, cond,
299 			     &perms);
300 		if (request & ~perms.allow)
301 			error = -EACCES;
302 	}
303 	error = aa_audit_file(profile, &perms, GFP_KERNEL, op, request, name,
304 			      NULL, cond->uid, info, error);
305 	kfree(buffer);
306 
307 	return error;
308 }
309 
310 /**
311  * xindex_is_subset - helper for aa_path_link
312  * @link: link permission set
313  * @target: target permission set
314  *
315  * test target x permissions are equal OR a subset of link x permissions
316  * this is done as part of the subset test, where a hardlink must have
317  * a subset of permissions that the target has.
318  *
319  * Returns: %1 if subset else %0
320  */
321 static inline bool xindex_is_subset(u32 link, u32 target)
322 {
323 	if (((link & ~AA_X_UNSAFE) != (target & ~AA_X_UNSAFE)) ||
324 	    ((link & AA_X_UNSAFE) && !(target & AA_X_UNSAFE)))
325 		return 0;
326 
327 	return 1;
328 }
329 
330 /**
331  * aa_path_link - Handle hard link permission check
332  * @profile: the profile being enforced  (NOT NULL)
333  * @old_dentry: the target dentry  (NOT NULL)
334  * @new_dir: directory the new link will be created in  (NOT NULL)
335  * @new_dentry: the link being created  (NOT NULL)
336  *
337  * Handle the permission test for a link & target pair.  Permission
338  * is encoded as a pair where the link permission is determined
339  * first, and if allowed, the target is tested.  The target test
340  * is done from the point of the link match (not start of DFA)
341  * making the target permission dependent on the link permission match.
342  *
343  * The subset test if required forces that permissions granted
344  * on link are a subset of the permission granted to target.
345  *
346  * Returns: %0 if allowed else error
347  */
348 int aa_path_link(struct aa_profile *profile, struct dentry *old_dentry,
349 		 struct path *new_dir, struct dentry *new_dentry)
350 {
351 	struct path link = { new_dir->mnt, new_dentry };
352 	struct path target = { new_dir->mnt, old_dentry };
353 	struct path_cond cond = {
354 		d_backing_inode(old_dentry)->i_uid,
355 		d_backing_inode(old_dentry)->i_mode
356 	};
357 	char *buffer = NULL, *buffer2 = NULL;
358 	const char *lname, *tname = NULL, *info = NULL;
359 	struct file_perms lperms, perms;
360 	u32 request = AA_MAY_LINK;
361 	unsigned int state;
362 	int error;
363 
364 	lperms = nullperms;
365 
366 	/* buffer freed below, lname is pointer in buffer */
367 	error = aa_path_name(&link, profile->path_flags, &buffer, &lname,
368 			     &info);
369 	if (error)
370 		goto audit;
371 
372 	/* buffer2 freed below, tname is pointer in buffer2 */
373 	error = aa_path_name(&target, profile->path_flags, &buffer2, &tname,
374 			     &info);
375 	if (error)
376 		goto audit;
377 
378 	error = -EACCES;
379 	/* aa_str_perms - handles the case of the dfa being NULL */
380 	state = aa_str_perms(profile->file.dfa, profile->file.start, lname,
381 			     &cond, &lperms);
382 
383 	if (!(lperms.allow & AA_MAY_LINK))
384 		goto audit;
385 
386 	/* test to see if target can be paired with link */
387 	state = aa_dfa_null_transition(profile->file.dfa, state);
388 	aa_str_perms(profile->file.dfa, state, tname, &cond, &perms);
389 
390 	/* force audit/quiet masks for link are stored in the second entry
391 	 * in the link pair.
392 	 */
393 	lperms.audit = perms.audit;
394 	lperms.quiet = perms.quiet;
395 	lperms.kill = perms.kill;
396 
397 	if (!(perms.allow & AA_MAY_LINK)) {
398 		info = "target restricted";
399 		goto audit;
400 	}
401 
402 	/* done if link subset test is not required */
403 	if (!(perms.allow & AA_LINK_SUBSET))
404 		goto done_tests;
405 
406 	/* Do link perm subset test requiring allowed permission on link are a
407 	 * subset of the allowed permissions on target.
408 	 */
409 	aa_str_perms(profile->file.dfa, profile->file.start, tname, &cond,
410 		     &perms);
411 
412 	/* AA_MAY_LINK is not considered in the subset test */
413 	request = lperms.allow & ~AA_MAY_LINK;
414 	lperms.allow &= perms.allow | AA_MAY_LINK;
415 
416 	request |= AA_AUDIT_FILE_MASK & (lperms.allow & ~perms.allow);
417 	if (request & ~lperms.allow) {
418 		goto audit;
419 	} else if ((lperms.allow & MAY_EXEC) &&
420 		   !xindex_is_subset(lperms.xindex, perms.xindex)) {
421 		lperms.allow &= ~MAY_EXEC;
422 		request |= MAY_EXEC;
423 		info = "link not subset of target";
424 		goto audit;
425 	}
426 
427 done_tests:
428 	error = 0;
429 
430 audit:
431 	error = aa_audit_file(profile, &lperms, GFP_KERNEL, OP_LINK, request,
432 			      lname, tname, cond.uid, info, error);
433 	kfree(buffer);
434 	kfree(buffer2);
435 
436 	return error;
437 }
438 
439 /**
440  * aa_file_perm - do permission revalidation check & audit for @file
441  * @op: operation being checked
442  * @profile: profile being enforced   (NOT NULL)
443  * @file: file to revalidate access permissions on  (NOT NULL)
444  * @request: requested permissions
445  *
446  * Returns: %0 if access allowed else error
447  */
448 int aa_file_perm(int op, struct aa_profile *profile, struct file *file,
449 		 u32 request)
450 {
451 	struct path_cond cond = {
452 		.uid = file_inode(file)->i_uid,
453 		.mode = file_inode(file)->i_mode
454 	};
455 
456 	return aa_path_perm(op, profile, &file->f_path, PATH_DELEGATE_DELETED,
457 			    request, &cond);
458 }
459