[postgis-tickets] [PostGIS] #3971: bias in kmeans

[PostGIS]

#3971: bias in kmeans
----------------------+---------------------------
  Reporter:  tilt     |      Owner:  pramsey
      Type:  defect   |     Status:  closed
  Priority:  medium   |  Milestone:  PostGIS 2.4.3
 Component:  postgis  |    Version:  2.4.x
Resolution:  fixed    |   Keywords:
----------------------+---------------------------

Comment (by Algunenano):

 Hi,

 I'm hitting a heap-buffer-overflow error because of these changes
 {{{
     ==1977==ERROR: AddressSanitizer: heap-buffer-overflow on address
 0x61f000002900 at pc 0x7f9825df18cd bp 0x7fff856d5be0 sp 0x7fff856d5bd0
     READ of size 8 at 0x61f000002900 thread T0
         #0 0x7f9825df18cc in lwkmeans_pt_distance
 /home/raul/dev/public/postgis/liblwgeom/lwkmeans.c:13
         #1 0x7f9825df27f0 in lwgeom_cluster_2d_kmeans
 /home/raul/dev/public/postgis/liblwgeom/lwkmeans.c:173
         #2 0x557ad2966598 in test_kmeans
 /home/raul/dev/public/postgis/liblwgeom/cunit/cu_algorithm.c:1339
         #3 0x7f9825881087 in run_single_test /tmp/yaourt-tmp-raul/aur-
 cunit/src/CUnit-2.1-3/CUnit/Sources/Framework/TestRun.c:991
         #4 0x7f98258812bd in run_single_suite /tmp/yaourt-tmp-raul/aur-
 cunit/src/CUnit-2.1-3/CUnit/Sources/Framework/TestRun.c:876
         #5 0x7f9825881736 in CU_run_all_tests /tmp/yaourt-tmp-raul/aur-
 cunit/src/CUnit-2.1-3/CUnit/Sources/Framework/TestRun.c:367
         #6 0x557ad29bf35c in main
 /home/raul/dev/public/postgis/liblwgeom/cunit/cu_tester.c:173
         #7 0x7f982519af49 in __libc_start_main
 (/usr/lib/libc.so.6+0x20f49)
         #8 0x557ad295c999 in _start
 (/home/raul/dev/public/postgis/liblwgeom/cunit/.libs/lt-cu_tester+0x3b999)

 }}}


 It appears it's passing a `void **` instead of a `void *`, so I've tried
 to fix it by changing the line to:
 {{{
 distances[j] += config.distance_method(config.objs[j],
 (Pointer)&centers_raw[i-1]);
 }}}
 But that reduces the cluster number from 12 to 7 so it doesn't pass the
 test.

--
Ticket URL: <https://trac.osgeo.org/postgis/ticket/3971#comment:12>
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