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storagefile: Fix backing format \0 check 

From qemu.git docs/interop/qcow2.txt

  == String header extensions ==

  Some header extensions (such as the backing file format name and
  the external data file name) are just a single string. In this case,
  the header extension length is the string length and the string is
  not '\0' terminated. (The header extension padding can make it look
  like a string is '\0' terminated, but neither is padding always
  necessary nor is there a guarantee that zero bytes are used
  for padding.)

So we shouldn't be checking for a \0 byte at the end of the backing
format section. I think in practice there always is a \0 but we
shouldn't depend on that.

Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Signed-off-by: Cole Robinson <crobinso@redhat.com>
This commit is contained in:
Cole Robinson 2019-10-04 19:41:36 -04:00
parent c87784be89
commit 9f0d364755
1 changed files with 12 additions and 6 deletions
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18
src/util/virstoragefile.c
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@ -503,15 +503,21 @@ qcow2GetExtensions(const char *buf,
break;
switch (magic) {
case QCOW2_HDR_EXTENSION_END:
goto done;
case QCOW2_HDR_EXTENSION_BACKING_FORMAT: {
VIR_AUTOFREE(char *) tmp = NULL;
if (VIR_ALLOC_N(tmp, len + 1) < 0)
return -1;
memcpy(tmp, buf + offset, len);
tmp[len] = '\0';
case QCOW2_HDR_EXTENSION_BACKING_FORMAT:
if (buf[offset+len] != '\0')
break;
*backingFormat = virStorageFileFormatTypeFromString(buf+offset);
*backingFormat = virStorageFileFormatTypeFromString(tmp);
if (*backingFormat <= VIR_STORAGE_FILE_NONE)
return -1;
break;
}
case QCOW2_HDR_EXTENSION_END:
goto done;
}
offset += len;