plugins/reflection/reflection.c

   1 /* nbdkit
   2  * Copyright (C) 2017-2019 Red Hat Inc.
   3  *
   4  * Redistribution and use in source and binary forms, with or without
   5  * modification, are permitted provided that the following conditions are
   6  * met:
   7  *
   8  * * Redistributions of source code must retain the above copyright
   9  * notice, this list of conditions and the following disclaimer.
  10  *
  11  * * Redistributions in binary form must reproduce the above copyright
  12  * notice, this list of conditions and the following disclaimer in the
  13  * documentation and/or other materials provided with the distribution.
  14  *
  15  * * Neither the name of Red Hat nor the names of its contributors may be
  16  * used to endorse or promote products derived from this software without
  17  * specific prior written permission.
  18  *
  19  * THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND
  20  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
  21  * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
  22  * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR
  23  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  24  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  25  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
  26  * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
  27  * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
  28  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
  29  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  30  * SUCH DAMAGE.
  31  */
  32
  33 #include <config.h>
  34
  35 #include <stdio.h>
  36 #include <stdlib.h>
  37 #include <string.h>
  38
  39 #if defined(HAVE_GNUTLS) && defined(HAVE_GNUTLS_BASE64_DECODE2)
  40 #include <gnutls/gnutls.h>
  41 #define HAVE_BASE64 1
  42 #endif
  43
  44 #define NBDKIT_API_VERSION 2
  45
  46 #include <nbdkit-plugin.h>
  47
  48 /* The mode. */
  49 enum mode {
  50   MODE_EXPORTNAME,
  51   MODE_BASE64EXPORTNAME,
  52 };
  53 static enum mode mode = MODE_EXPORTNAME;
  54
  55 static int
  56 reflection_config (const char *key, const char *value)
  57 {
  58   if (strcmp (key, "mode") == 0) {
  59     if (strcasecmp (value, "exportname") == 0 ||
  60         strcasecmp (value, "export-name") == 0) {
  61       mode = MODE_EXPORTNAME;
  62     }
  63     else if (strcasecmp (value, "base64exportname") == 0 ||
  64              strcasecmp (value, "base64-export-name") == 0) {
  65 #ifdef HAVE_BASE64
  66       mode = MODE_BASE64EXPORTNAME;
  67 #else
  68       nbdkit_error ("the plugin was compiled without base64 support");
  69       return -1;
  70 #endif
  71     }
  72     else {
  73       nbdkit_error ("unknown mode: '%s'", value);
  74       return -1;
  75     }
  76   }
  77   else {
  78     nbdkit_error ("unknown parameter '%s'", key);
  79     return -1;
  80   }
  81
  82   return 0;
  83 }
  84
  85 #define reflection_config_help \
  86   "mode=exportname|base64exportname  Plugin mode."
  87
  88 /* Provide a way to detect if the base64 feature is supported. */
  89 static void
  90 reflection_dump_plugin (void)
  91 {
  92 #ifdef HAVE_BASE64
  93   printf ("reflection_base64=yes\n");
  94 #endif
  95 }
  96
  97 /* Per-connection handle. */
  98 struct handle {
  99   void *data;                   /* Block device data. */
 100   size_t len;                   /* Length of data in bytes. */
 101 };
 102
 103 static int
 104 decode_base64 (const char *data, size_t len, struct handle *ret)
 105 {
 106 #ifdef HAVE_BASE64
 107   gnutls_datum_t in, out;
 108   int err;
 109
 110   /* For unclear reasons gnutls_base64_decode2 won't handle an empty
 111    * string, even though base64("") == "".
 112    * https://tools.ietf.org/html/rfc4648#section-10
 113    * https://gitlab.com/gnutls/gnutls/issues/834
 114    * So we have to special-case it.
 115    */
 116   if (len == 0) {
 117     ret->data = NULL;
 118     ret->len = 0;
 119     return 0;
 120   }
 121
 122   in.data = (unsigned char *) data;
 123   in.size = len;
 124   err = gnutls_base64_decode2 (&in, &out);
 125   if (err != GNUTLS_E_SUCCESS) {
 126     nbdkit_error ("base64: %s", gnutls_strerror (err));
 127     /* We don't have to free out.data.  I verified that it is freed on
 128      * the error path of gnutls_base64_decode2.
 129      */
 130     return -1;
 131   }
 132
 133   ret->data = out.data;         /* caller frees, eventually */
 134   ret->len = out.size;
 135   return 0;
 136 #else
 137   nbdkit_error ("the plugin was compiled without base64 support");
 138   return -1;
 139 #endif
 140 }
 141
 142 /* Create the per-connection handle.
 143  *
 144  * This is a rather unusual plugin because it has to parse data sent
 145  * by the client.  For security reasons, be careful about:
 146  *
 147  * - Returning more data than is sent by the client.
 148  *
 149  * - Inputs that result in unbounded output.
 150  *
 151  * - Inputs that could hang, crash or exploit the server.
 152  */
 153 static void *
 154 reflection_open (int readonly)
 155 {
 156   const char *export_name;
 157   size_t export_name_len;
 158   struct handle *h;
 159
 160   h = malloc (sizeof *h);
 161   if (h == NULL) {
 162     nbdkit_error ("malloc: %m");
 163     return NULL;
 164   }
 165
 166   switch (mode) {
 167   case MODE_EXPORTNAME:
 168   case MODE_BASE64EXPORTNAME:
 169     export_name = nbdkit_export_name ();
 170     if (export_name == NULL) {
 171       free (h);
 172       return NULL;
 173     }
 174     export_name_len = strlen (export_name);
 175
 176     if (mode == MODE_EXPORTNAME) {
 177       h->len = export_name_len;
 178       h->data = strdup (export_name);
 179       if (h->data == NULL) {
 180         nbdkit_error ("strdup: %m");
 181         free (h);
 182         return NULL;
 183       }
 184       return h;
 185     }
 186     else /* mode == MODE_BASE64EXPORTNAME */ {
 187       if (decode_base64 (export_name, export_name_len, h) == -1) {
 188         free (h);
 189         return NULL;
 190       }
 191       return h;
 192     }
 193
 194   default:
 195     abort ();
 196   }
 197 }
 198
 199 /* Close the per-connection handle. */
 200 static void
 201 reflection_close (void *handle)
 202 {
 203   struct handle *h = handle;
 204
 205   free (h->data);
 206   free (h);
 207 }
 208
 209 #define THREAD_MODEL NBDKIT_THREAD_MODEL_PARALLEL
 210
 211 /* Get the disk size. */
 212 static int64_t
 213 reflection_get_size (void *handle)
 214 {
 215   struct handle *h = handle;
 216
 217   return (int64_t) h->len;
 218 }
 219
 220 /* Read-only plugin so multi-conn is safe. */
 221 static int
 222 reflection_can_multi_conn (void *handle)
 223 {
 224   return 1;
 225 }
 226
 227 /* Cache. */
 228 static int
 229 reflection_can_cache (void *handle)
 230 {
 231   /* Everything is already in memory, returning this without
 232    * implementing .cache lets nbdkit do the correct no-op.
 233    */
 234   return NBDKIT_CACHE_NATIVE;
 235 }
 236
 237 /* Read data. */
 238 static int
 239 reflection_pread (void *handle, void *buf, uint32_t count, uint64_t offset,
 240                   uint32_t flags)
 241 {
 242   struct handle *h = handle;
 243
 244   memcpy (buf, h->data + offset, count);
 245   return 0;
 246 }
 247
 248 static struct nbdkit_plugin plugin = {
 249   .name              = "reflection",
 250   .version           = PACKAGE_VERSION,
 251   .config            = reflection_config,
 252   .config_help       = reflection_config_help,
 253   .dump_plugin       = reflection_dump_plugin,
 254   .magic_config_key  = "mode",
 255   .open              = reflection_open,
 256   .close             = reflection_close,
 257   .get_size          = reflection_get_size,
 258   .can_multi_conn    = reflection_can_multi_conn,
 259   .can_cache         = reflection_can_cache,
 260   .pread             = reflection_pread,
 261   /* In this plugin, errno is preserved properly along error return
 262    * paths from failed system calls.
 263    */
 264   .errno_is_preserved = 1,
 265 };
 266
 267 NBDKIT_REGISTER_PLUGIN(plugin)