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