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