[postgis-tickets] [PostGIS] #3970: Undefined behaviour in lwcollection.c and lwpoly.c

[PostGIS]

#3970: Undefined behaviour in lwcollection.c and lwpoly.c
-------------------------+---------------------------
  Reporter:  Algunenano  |      Owner:  strk
      Type:  defect      |     Status:  new
  Priority:  medium      |  Milestone:  PostGIS 2.5.0
 Component:  liblwgeom   |    Version:  trunk
Resolution:              |   Keywords:
-------------------------+---------------------------

Comment (by Algunenano):

 In `gserialized_from_lwcollection` it is written as `uint32_t`
 {{{
         /* Write in the number of subgeoms. */
         memcpy(loc, &coll->ngeoms, sizeof(uint32_t));
         loc += sizeof(uint32_t);
 }}}

 Then it's read as an `uint32_t` and implicitly casted to `int` in
 `lwcollection_from_gserialized_buffer`:
 {{{
         ngeoms = gserialized_get_uint32_t(data_ptr);
         collection->ngeoms = ngeoms; /* Zero => empty geometry */
 }}}

 I'm all about changing it to unsigned, but I'd rather use the `uint32_t`
 and be sure it's 4 bytes.

 Since that change (either way) requires a lot of modifications I'd rather
 do it in another ticket. It was being discussed in the mailing list
 (http://lists.osgeo.org/pipermail/postgis-devel/2017-December/026773.html)
 but I don't think anyone is working on it.

--
Ticket URL: <https://trac.osgeo.org/postgis/ticket/3970#comment:2>
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