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Linux/security/apparmor/path.c

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  1 /*
  2  * AppArmor security module
  3  *
  4  * This file contains AppArmor function for pathnames
  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 <linux/magic.h>
 16 #include <linux/mount.h>
 17 #include <linux/namei.h>
 18 #include <linux/nsproxy.h>
 19 #include <linux/path.h>
 20 #include <linux/sched.h>
 21 #include <linux/slab.h>
 22 #include <linux/fs_struct.h>
 23 
 24 #include "include/apparmor.h"
 25 #include "include/path.h"
 26 #include "include/policy.h"
 27 
 28 
 29 /* modified from dcache.c */
 30 static int prepend(char **buffer, int buflen, const char *str, int namelen)
 31 {
 32         buflen -= namelen;
 33         if (buflen < 0)
 34                 return -ENAMETOOLONG;
 35         *buffer -= namelen;
 36         memcpy(*buffer, str, namelen);
 37         return 0;
 38 }
 39 
 40 #define CHROOT_NSCONNECT (PATH_CHROOT_REL | PATH_CHROOT_NSCONNECT)
 41 
 42 /**
 43  * d_namespace_path - lookup a name associated with a given path
 44  * @path: path to lookup  (NOT NULL)
 45  * @buf:  buffer to store path to  (NOT NULL)
 46  * @buflen: length of @buf
 47  * @name: Returns - pointer for start of path name with in @buf (NOT NULL)
 48  * @flags: flags controlling path lookup
 49  *
 50  * Handle path name lookup.
 51  *
 52  * Returns: %0 else error code if path lookup fails
 53  *          When no error the path name is returned in @name which points to
 54  *          to a position in @buf
 55  */
 56 static int d_namespace_path(struct path *path, char *buf, int buflen,
 57                             char **name, int flags)
 58 {
 59         char *res;
 60         int error = 0;
 61         int connected = 1;
 62 
 63         if (path->mnt->mnt_flags & MNT_INTERNAL) {
 64                 /* it's not mounted anywhere */
 65                 res = dentry_path(path->dentry, buf, buflen);
 66                 *name = res;
 67                 if (IS_ERR(res)) {
 68                         *name = buf;
 69                         return PTR_ERR(res);
 70                 }
 71                 if (path->dentry->d_sb->s_magic == PROC_SUPER_MAGIC &&
 72                     strncmp(*name, "/sys/", 5) == 0) {
 73                         /* TODO: convert over to using a per namespace
 74                          * control instead of hard coded /proc
 75                          */
 76                         return prepend(name, *name - buf, "/proc", 5);
 77                 }
 78                 return 0;
 79         }
 80 
 81         /* resolve paths relative to chroot?*/
 82         if (flags & PATH_CHROOT_REL) {
 83                 struct path root;
 84                 get_fs_root(current->fs, &root);
 85                 res = __d_path(path, &root, buf, buflen);
 86                 path_put(&root);
 87         } else {
 88                 res = d_absolute_path(path, buf, buflen);
 89                 if (!our_mnt(path->mnt))
 90                         connected = 0;
 91         }
 92 
 93         /* handle error conditions - and still allow a partial path to
 94          * be returned.
 95          */
 96         if (!res || IS_ERR(res)) {
 97                 if (PTR_ERR(res) == -ENAMETOOLONG)
 98                         return -ENAMETOOLONG;
 99                 connected = 0;
100                 res = dentry_path_raw(path->dentry, buf, buflen);
101                 if (IS_ERR(res)) {
102                         error = PTR_ERR(res);
103                         *name = buf;
104                         goto out;
105                 };
106         } else if (!our_mnt(path->mnt))
107                 connected = 0;
108 
109         *name = res;
110 
111         /* Handle two cases:
112          * 1. A deleted dentry && profile is not allowing mediation of deleted
113          * 2. On some filesystems, newly allocated dentries appear to the
114          *    security_path hooks as a deleted dentry except without an inode
115          *    allocated.
116          */
117         if (d_unlinked(path->dentry) && path->dentry->d_inode &&
118             !(flags & PATH_MEDIATE_DELETED)) {
119                         error = -ENOENT;
120                         goto out;
121         }
122 
123         /* If the path is not connected to the expected root,
124          * check if it is a sysctl and handle specially else remove any
125          * leading / that __d_path may have returned.
126          * Unless
127          *     specifically directed to connect the path,
128          * OR
129          *     if in a chroot and doing chroot relative paths and the path
130          *     resolves to the namespace root (would be connected outside
131          *     of chroot) and specifically directed to connect paths to
132          *     namespace root.
133          */
134         if (!connected) {
135                 if (!(flags & PATH_CONNECT_PATH) &&
136                            !(((flags & CHROOT_NSCONNECT) == CHROOT_NSCONNECT) &&
137                              our_mnt(path->mnt))) {
138                         /* disconnected path, don't return pathname starting
139                          * with '/'
140                          */
141                         error = -EACCES;
142                         if (*res == '/')
143                                 *name = res + 1;
144                 }
145         }
146 
147 out:
148         return error;
149 }
150 
151 /**
152  * get_name_to_buffer - get the pathname to a buffer ensure dir / is appended
153  * @path: path to get name for  (NOT NULL)
154  * @flags: flags controlling path lookup
155  * @buffer: buffer to put name in  (NOT NULL)
156  * @size: size of buffer
157  * @name: Returns - contains position of path name in @buffer (NOT NULL)
158  *
159  * Returns: %0 else error on failure
160  */
161 static int get_name_to_buffer(struct path *path, int flags, char *buffer,
162                               int size, char **name, const char **info)
163 {
164         int adjust = (flags & PATH_IS_DIR) ? 1 : 0;
165         int error = d_namespace_path(path, buffer, size - adjust, name, flags);
166 
167         if (!error && (flags & PATH_IS_DIR) && (*name)[1] != '\0')
168                 /*
169                  * Append "/" to the pathname.  The root directory is a special
170                  * case; it already ends in slash.
171                  */
172                 strcpy(&buffer[size - 2], "/");
173 
174         if (info && error) {
175                 if (error == -ENOENT)
176                         *info = "Failed name lookup - deleted entry";
177                 else if (error == -EACCES)
178                         *info = "Failed name lookup - disconnected path";
179                 else if (error == -ENAMETOOLONG)
180                         *info = "Failed name lookup - name too long";
181                 else
182                         *info = "Failed name lookup";
183         }
184 
185         return error;
186 }
187 
188 /**
189  * aa_path_name - compute the pathname of a file
190  * @path: path the file  (NOT NULL)
191  * @flags: flags controlling path name generation
192  * @buffer: buffer that aa_get_name() allocated  (NOT NULL)
193  * @name: Returns - the generated path name if !error (NOT NULL)
194  * @info: Returns - information on why the path lookup failed (MAYBE NULL)
195  *
196  * @name is a pointer to the beginning of the pathname (which usually differs
197  * from the beginning of the buffer), or NULL.  If there is an error @name
198  * may contain a partial or invalid name that can be used for audit purposes,
199  * but it can not be used for mediation.
200  *
201  * We need PATH_IS_DIR to indicate whether the file is a directory or not
202  * because the file may not yet exist, and so we cannot check the inode's
203  * file type.
204  *
205  * Returns: %0 else error code if could retrieve name
206  */
207 int aa_path_name(struct path *path, int flags, char **buffer, const char **name,
208                  const char **info)
209 {
210         char *buf, *str = NULL;
211         int size = 256;
212         int error;
213 
214         *name = NULL;
215         *buffer = NULL;
216         for (;;) {
217                 /* freed by caller */
218                 buf = kmalloc(size, GFP_KERNEL);
219                 if (!buf)
220                         return -ENOMEM;
221 
222                 error = get_name_to_buffer(path, flags, buf, size, &str, info);
223                 if (error != -ENAMETOOLONG)
224                         break;
225 
226                 kfree(buf);
227                 size <<= 1;
228                 if (size > aa_g_path_max)
229                         return -ENAMETOOLONG;
230                 *info = NULL;
231         }
232         *buffer = buf;
233         *name = str;
234 
235         return error;
236 }
237 

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