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Fix misbehavior in contrib/pg_trgm with an unsatisfiable regex.

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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
This commit is contained in:
Tom Lane
2023-03-11 12:15:41 -05:00
parent 866fd004d9
commit bc436e4a91
3 changed files with 25 additions and 10 deletions
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26
contrib/pg_trgm/trgm_regexp.c
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@ -1929,9 +1929,7 @@ 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,
@ -2003,17 +2001,25 @@ 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 *)