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         struct path root, tmp;
  61         char *res;
  62         int connected, error = 0;
  63
  64         /* Get the root we want to resolve too, released below */
  65         if (flags & PATH_CHROOT_REL) {
  66                 /* resolve paths relative to chroot */
  67                 get_fs_root(current->fs, &root);
  68         } else {
  69                 /* resolve paths relative to namespace */
  70                 root.mnt = current->nsproxy->mnt_ns->root;
  71                 root.dentry = root.mnt->mnt_root;
  72                 path_get(&root);
  73         }
  74
  75         spin_lock(&dcache_lock);
  76         tmp = root;
  77         res = __d_path(path, &tmp, buf, buflen);
  78         spin_unlock(&dcache_lock);
  79
  80         *name = res;
  81         /* handle error conditions - and still allow a partial path to
  82          * be returned.
  83          */
  84         if (IS_ERR(res)) {
  85                 error = PTR_ERR(res);
  86                 *name = buf;
  87                 goto out;
  88         }
  89
  90         /* Handle two cases:
  91          * 1. A deleted dentry && profile is not allowing mediation of deleted
  92          * 2. On some filesystems, newly allocated dentries appear to the
  93          *    security_path hooks as a deleted dentry except without an inode
  94          *    allocated.
  95          */
  96         if (d_unlinked(path->dentry) && path->dentry->d_inode &&
  97             !(flags & PATH_MEDIATE_DELETED)) {
  98                         error = -ENOENT;
  99                         goto out;
 100         }
 101
 102         /* Determine if the path is connected to the expected root */
 103         connected = tmp.dentry == root.dentry && tmp.mnt == root.mnt;
 104
 105         /* If the path is not connected,
 106          * check if it is a sysctl and handle specially else remove any
 107          * leading / that __d_path may have returned.
 108          * Unless
 109          *     specifically directed to connect the path,
 110          * OR
 111          *     if in a chroot and doing chroot relative paths and the path
 112          *     resolves to the namespace root (would be connected outside
 113          *     of chroot) and specifically directed to connect paths to
 114          *     namespace root.
 115          */
 116         if (!connected) {
 117                 /* is the disconnect path a sysctl? */
 118                 if (tmp.dentry->d_sb->s_magic == PROC_SUPER_MAGIC &&
 119                     strncmp(*name, "/sys/", 5) == 0) {
 120                         /* TODO: convert over to using a per namespace
 121                          * control instead of hard coded /proc
 122                          */
 123                         error = prepend(name, *name - buf, "/proc", 5);
 124                 } else if (!(flags & PATH_CONNECT_PATH) &&
 125                            !(((flags & CHROOT_NSCONNECT) == CHROOT_NSCONNECT) &&
 126                              (tmp.mnt == current->nsproxy->mnt_ns->root &&
 127                               tmp.dentry == tmp.mnt->mnt_root))) {
 128                         /* disconnected path, don't return pathname starting
 129                          * with '/'
 130                          */
 131                         error = -ESTALE;
 132                         if (*res == '/')
 133                                 *name = res + 1;
 134                 }
 135         }
 136
 137 out:
 138         path_put(&root);
 139
 140         return error;
 141 }
 142
 143 /**
 144  * get_name_to_buffer - get the pathname to a buffer ensure dir / is appended
 145  * @path: path to get name for  (NOT NULL)
 146  * @flags: flags controlling path lookup
 147  * @buffer: buffer to put name in  (NOT NULL)
 148  * @size: size of buffer
 149  * @name: Returns - contains position of path name in @buffer (NOT NULL)
 150  *
 151  * Returns: %0 else error on failure
 152  */
 153 static int get_name_to_buffer(struct path *path, int flags, char *buffer,
 154                               int size, char **name)
 155 {
 156         int adjust = (flags & PATH_IS_DIR) ? 1 : 0;
 157         int error = d_namespace_path(path, buffer, size - adjust, name, flags);
 158
 159         if (!error && (flags & PATH_IS_DIR) && (*name)[1] != '\0')
 160                 /*
 161                  * Append "/" to the pathname.  The root directory is a special
 162                  * case; it already ends in slash.
 163                  */
 164                 strcpy(&buffer[size - 2], "/");
 165
 166         return error;
 167 }
 168
 169 /**
 170  * aa_get_name - compute the pathname of a file
 171  * @path: path the file  (NOT NULL)
 172  * @flags: flags controlling path name generation
 173  * @buffer: buffer that aa_get_name() allocated  (NOT NULL)
 174  * @name: Returns - the generated path name if !error (NOT NULL)
 175  *
 176  * @name is a pointer to the beginning of the pathname (which usually differs
 177  * from the beginning of the buffer), or NULL.  If there is an error @name
 178  * may contain a partial or invalid name that can be used for audit purposes,
 179  * but it can not be used for mediation.
 180  *
 181  * We need PATH_IS_DIR to indicate whether the file is a directory or not
 182  * because the file may not yet exist, and so we cannot check the inode's
 183  * file type.
 184  *
 185  * Returns: %0 else error code if could retrieve name
 186  */
 187 int aa_get_name(struct path *path, int flags, char **buffer, const char **name)
 188 {
 189         char *buf, *str = NULL;
 190         int size = 256;
 191         int error;
 192
 193         *name = NULL;
 194         *buffer = NULL;
 195         for (;;) {
 196                 /* freed by caller */
 197                 buf = kmalloc(size, GFP_KERNEL);
 198                 if (!buf)
 199                         return -ENOMEM;
 200
 201                 error = get_name_to_buffer(path, flags, buf, size, &str);
 202                 if (error != -ENAMETOOLONG)
 203                         break;
 204
 205                 kfree(buf);
 206                 size <<= 1;
 207                 if (size > aa_g_path_max)
 208                         return -ENAMETOOLONG;
 209         }
 210         *buffer = buf;
 211         *name = str;
 212
 213         return error;
 214 }