Fix recently-exposed portability issue in regex optimization. fixempties() counts the number of in-arcs in the regex NFA and then allocates an array of that many arc pointers. If the NFA contains no arcs, this amounts to malloc(0) for which some platforms return NULL. The code mistakenly treats that as indicating out-of-memory. Thus, we can get a bogus "out of memory" failure for some unsatisfiable regexes.
This happens only in v15 and earlier, since bea3d7e38 switched to using palloc() rather than bare malloc(). And at least of the platforms in the buildfarm, only AIX seems to return NULL. So the impact is pretty narrow. But I don't especially want to ship code that is failing its own regression tests, so let's fix this for this week's releases. A quick code survey says that there is only the one place in src/backend/regex/ that is at risk of doing malloc(0), so we'll just band-aid that place. A more future-proof fix could be to install a malloc() wrapper similar to pg_malloc(). But this code seems unlikely to change much more in the affected branches, so that's probably overkill. The only known test case for this involves a complemented character class in a bracket expression, for example [^\s\S], and we didn't support that in v13. So it may be that the problem is unreachable in v13. But I'm not 100% sure of that, so patch v13 too. Discussion: https://postgr.es/m/661fd81b-f069-8f30-1a41-e195c5744...@gmail.com Branch ------ REL_15_STABLE Details ------- https://git.postgresql.org/pg/commitdiff/6ab39c02747c33173e5e33291e66cebbdbc75d82 Modified Files -------------- src/backend/regex/regc_nfa.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
