security/apparmor/path.c

   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                 if (res && !IS_ERR(res)) {
  87                         /* everything's fine */
  88                         *name = res;
  89                         path_put(&root);
  90                         goto ok;
  91                 }
  92                 path_put(&root);
  93                 connected = 0;
  94         }
  95
  96         res = d_absolute_path(path, buf, buflen);
  97
  98         *name = res;
  99         /* handle error conditions - and still allow a partial path to
 100          * be returned.
 101          */
 102         if (IS_ERR(res)) {
 103                 error = PTR_ERR(res);
 104                 *name = buf;
 105                 goto out;
 106         }
 107         if (!our_mnt(path->mnt))
 108                 connected = 0;
 109
 110 ok:
 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 = -ESTALE;
 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)
 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         return error;
 175 }
 176
 177 /**
 178  * aa_get_name - compute the pathname of a file
 179  * @path: path the file  (NOT NULL)
 180  * @flags: flags controlling path name generation
 181  * @buffer: buffer that aa_get_name() allocated  (NOT NULL)
 182  * @name: Returns - the generated path name if !error (NOT NULL)
 183  *
 184  * @name is a pointer to the beginning of the pathname (which usually differs
 185  * from the beginning of the buffer), or NULL.  If there is an error @name
 186  * may contain a partial or invalid name that can be used for audit purposes,
 187  * but it can not be used for mediation.
 188  *
 189  * We need PATH_IS_DIR to indicate whether the file is a directory or not
 190  * because the file may not yet exist, and so we cannot check the inode's
 191  * file type.
 192  *
 193  * Returns: %0 else error code if could retrieve name
 194  */
 195 int aa_get_name(struct path *path, int flags, char **buffer, const char **name)
 196 {
 197         char *buf, *str = NULL;
 198         int size = 256;
 199         int error;
 200
 201         *name = NULL;
 202         *buffer = NULL;
 203         for (;;) {
 204                 /* freed by caller */
 205                 buf = kmalloc(size, GFP_KERNEL);
 206                 if (!buf)
 207                         return -ENOMEM;
 208
 209                 error = get_name_to_buffer(path, flags, buf, size, &str);
 210                 if (error != -ENAMETOOLONG)
 211                         break;
 212
 213                 kfree(buf);
 214                 size <<= 1;
 215                 if (size > aa_g_path_max)
 216                         return -ENAMETOOLONG;
 217         }
 218         *buffer = buf;
 219         *name = str;
 220
 221         return error;
 222 }