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dmg: prevent chunk buffer overflow (CVE-2014-0145) 

Both compressed and uncompressed I/O is buffered.  dmg_open() calculates
the maximum buffer size needed from the metadata in the image file.

There is currently a buffer overflow since ->lengths[] is accounted
against the maximum compressed buffer size but actually uses the
uncompressed buffer:

  switch (s->types[chunk]) {
  case 1: /* copy */
      ret = bdrv_pread(bs->file, s->offsets[chunk],
                       s->uncompressed_chunk, s->lengths[chunk]);

We must account against the maximum uncompressed buffer size for type=1
chunks.

This patch fixes the maximum buffer size calculation to take into
account the chunk type.  It is critical that we update the correct
maximum since there are two buffers ->compressed_chunk and
->uncompressed_chunk.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2014-03-26 13:06:00 +01:00
parent 686d7148ec
commit f0dce23475
1 changed files with 33 additions and 6 deletions
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39
block/dmg.c
View File

@ -100,6 +100,37 @@ static int read_uint32(BlockDriverState *bs, int64_t offset, uint32_t *result)
return 0;
}
/* Increase max chunk sizes, if necessary. This function is used to calculate
* the buffer sizes needed for compressed/uncompressed chunk I/O.
*/
static void update_max_chunk_size(BDRVDMGState *s, uint32_t chunk,
uint32_t *max_compressed_size,
uint32_t *max_sectors_per_chunk)
{
uint32_t compressed_size = 0;
uint32_t uncompressed_sectors = 0;
switch (s->types[chunk]) {
case 0x80000005: /* zlib compressed */
compressed_size = s->lengths[chunk];
uncompressed_sectors = s->sectorcounts[chunk];
break;
case 1: /* copy */
uncompressed_sectors = (s->lengths[chunk] + 511) / 512;
break;
case 2: /* zero */
uncompressed_sectors = s->sectorcounts[chunk];
break;
}
if (compressed_size > *max_compressed_size) {
*max_compressed_size = compressed_size;
}
if (uncompressed_sectors > *max_sectors_per_chunk) {
*max_sectors_per_chunk = uncompressed_sectors;
}
}
static int dmg_open(BlockDriverState *bs, QDict *options, int flags,
Error **errp)
{
@ -245,12 +276,8 @@ static int dmg_open(BlockDriverState *bs, QDict *options, int flags,
goto fail;
}
if (s->lengths[i] > max_compressed_size) {
max_compressed_size = s->lengths[i];
}
if (s->sectorcounts[i] > max_sectors_per_chunk) {
max_sectors_per_chunk = s->sectorcounts[i];
}
update_max_chunk_size(s, i, &max_compressed_size,
&max_sectors_per_chunk);
}
s->n_chunks += chunk_count;
}