Fix misbehavior in contrib/pg_trgm with an unsatisfiable regex.

If the regex compiler can see that a regex is unsatisfiable
(for example, '$foo') then it may emit an NFA having no arcs.
pg_trgm's packGraph function did the wrong thing in this case;
it would access off the end of a work array, and with bad luck
could produce a corrupted output data structure causing more
problems later.  This could end with wrong answers or crashes
in queries using a pg_trgm GIN or GiST index with such a regex.

Fix by not trying to de-duplicate if there aren't at least 2 arcs.

Per bug #17830 from Alexander Lakhin.  Back-patch to all supported
branches.

Discussion: https://postgr.es/m/17830-57ff5f89bdb02b09@postgresql.org

diff --git a/contrib/pg_trgm/expected/pg_word_trgm.out b/contrib/pg_trgm/expected/pg_word_trgm.out
index 936d489390e401cb09824191b077f55671112f6c..c66a67f30efd44d061ce5972305d07f5bf84c230 100644 (file)
--- a/contrib/pg_trgm/expected/pg_word_trgm.out
+++ b/contrib/pg_trgm/expected/pg_word_trgm.out
@@ -1044,3 +1044,9 @@ select t,word_similarity('Kabankala',t) as sml from test_trgm2 where t %> 'Kaban
  Waikala                          |      0.3
 (89 rows)
 
+-- test unsatisfiable pattern
+select * from test_trgm2 where t ~ '.*$x';
+ t 
+---
+(0 rows)
+

diff --git a/contrib/pg_trgm/sql/pg_word_trgm.sql b/contrib/pg_trgm/sql/pg_word_trgm.sql
index d9fa1c55e5e7995791bcd0694f5a184ecdca4d67..d2ada49133a80c3477693f1dd4810367a55e4235 100644 (file)
--- a/contrib/pg_trgm/sql/pg_word_trgm.sql
+++ b/contrib/pg_trgm/sql/pg_word_trgm.sql
@@ -43,3 +43,6 @@ select t,word_similarity('Baykal',t) as sml from test_trgm2 where 'Baykal' <% t
 select t,word_similarity('Kabankala',t) as sml from test_trgm2 where 'Kabankala' <% t order by sml desc, t;
 select t,word_similarity('Baykal',t) as sml from test_trgm2 where t %> 'Baykal' order by sml desc, t;
 select t,word_similarity('Kabankala',t) as sml from test_trgm2 where t %> 'Kabankala' order by sml desc, t;
+
+-- test unsatisfiable pattern
+select * from test_trgm2 where t ~ '.*$x';

diff --git a/contrib/pg_trgm/trgm_regexp.c b/contrib/pg_trgm/trgm_regexp.c
index 9a00564ae4fc9ade3e2acb58c6b2ae55294144d6..06cd3db67beeded09ca70df0731ad965b450f381 100644 (file)
--- a/contrib/pg_trgm/trgm_regexp.c
+++ b/contrib/pg_trgm/trgm_regexp.c
@@ -1947,9 +1947,7 @@ packGraph(TrgmNFA *trgmNFA, MemoryContext rcontext)
                                arcsCount;
        HASH_SEQ_STATUS scan_status;
        TrgmState  *state;
-       TrgmPackArcInfo *arcs,
-                          *p1,
-                          *p2;
+       TrgmPackArcInfo *arcs;
        TrgmPackedArc *packedArcs;
        TrgmPackedGraph *result;
        int                     i,
@@ -2021,17 +2019,25 @@ packGraph(TrgmNFA *trgmNFA, MemoryContext rcontext)
        qsort(arcs, arcIndex, sizeof(TrgmPackArcInfo), packArcInfoCmp);
 
        /* We could have duplicates because states were merged. Remove them. */
-       /* p1 is probe point, p2 is last known non-duplicate. */
-       p2 = arcs;
-       for (p1 = arcs + 1; p1 < arcs + arcIndex; p1++)
+       if (arcIndex > 1)
        {
-               if (packArcInfoCmp(p1, p2) > 0)
+               /* p1 is probe point, p2 is last known non-duplicate. */
+               TrgmPackArcInfo *p1,
+                                  *p2;
+
+               p2 = arcs;
+               for (p1 = arcs + 1; p1 < arcs + arcIndex; p1++)
                {
-                       p2++;
-                       *p2 = *p1;
+                       if (packArcInfoCmp(p1, p2) > 0)
+                       {
+                               p2++;
+                               *p2 = *p1;
+                       }
                }
+               arcsCount = (p2 - arcs) + 1;
        }
-       arcsCount = (p2 - arcs) + 1;
+       else
+               arcsCount = arcIndex;
 
        /* Create packed representation */
        result = (TrgmPackedGraph *)