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Further tweak memory management for regex DFAs.

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Coverity is still unhappy after commit 190c79884, and after looking
closer I think it might be onto something.  The callers of newdfa()
typically drop out if v->err has been set nonzero, which newdfa()
is faithfully doing if it fails.  However, what if v->err was already
nonzero before we entered newdfa()?  Then newdfa() could succeed and
the caller would promptly leak its result.

I don't think this scenario can actually happen, but the predicate
"v->err is always zero when newdfa() is called" seems difficult to be
entirely sure of; there's a good deal of code that potentially could
get that wrong.

It seems better to adjust the callers to directly check for a null
result instead of relying on ISERR() tests.  This is slightly cheaper
than the previous coding anyway.

Lacking evidence that there's any real bug, no back-patch.
This commit is contained in:
Tom Lane 2021-03-08 16:32:29 -05:00
parent 8a812e5106
commit 6c20bdb2a2
2 changed files with 10 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
src/backend/regex/rege_dfa.c
View File

@ -604,6 +604,8 @@ lastcold(struct vars *v,
/* /*
* newdfa - set up a fresh DFA * newdfa - set up a fresh DFA
*
* Returns NULL (and sets v->err) on failure.
*/ */
static struct dfa * static struct dfa *
newdfa(struct vars *v, newdfa(struct vars *v,

18
src/backend/regex/regexec.c
View File

@ -351,7 +351,7 @@ getsubdfa(struct vars *v,
if (d == NULL) if (d == NULL)
{ {
d = newdfa(v, &t->cnfa, &v->g->cmap, DOMALLOC); d = newdfa(v, &t->cnfa, &v->g->cmap, DOMALLOC);
if (ISERR()) if (d == NULL)
return NULL; return NULL;
/* set up additional info if this is a backref node */ /* set up additional info if this is a backref node */
if (t->op == 'b') if (t->op == 'b')
@ -381,8 +381,6 @@ getladfa(struct vars *v,
struct subre *sub = &v->g->lacons[n]; struct subre *sub = &v->g->lacons[n];
v->ladfas[n] = newdfa(v, &sub->cnfa, &v->g->cmap, DOMALLOC); v->ladfas[n] = newdfa(v, &sub->cnfa, &v->g->cmap, DOMALLOC);
if (ISERR())
return NULL;
/* a LACON can't contain a backref, so nothing else to do */ /* a LACON can't contain a backref, so nothing else to do */
} }
return v->ladfas[n]; return v->ladfas[n];
@ -408,8 +406,8 @@ find(struct vars *v,
/* first, a shot with the search RE */ /* first, a shot with the search RE */
s = newdfa(v, &v->g->search, cm, &v->dfa1); s = newdfa(v, &v->g->search, cm, &v->dfa1);
assert(!(ISERR() && s != NULL)); if (s == NULL)
NOERR(); return v->err;
MDEBUG(("\nsearch at %ld\n", LOFF(v->start))); MDEBUG(("\nsearch at %ld\n", LOFF(v->start)));
cold = NULL; cold = NULL;
close = shortest(v, s, v->search_start, v->search_start, v->stop, close = shortest(v, s, v->search_start, v->search_start, v->stop,
@ -436,8 +434,8 @@ find(struct vars *v,
cold = NULL; cold = NULL;
MDEBUG(("between %ld and %ld\n", LOFF(open), LOFF(close))); MDEBUG(("between %ld and %ld\n", LOFF(open), LOFF(close)));
d = newdfa(v, cnfa, cm, &v->dfa1); d = newdfa(v, cnfa, cm, &v->dfa1);
assert(!(ISERR() && d != NULL)); if (d == NULL)
NOERR(); return v->err;
for (begin = open; begin <= close; begin++) for (begin = open; begin <= close; begin++)
{ {
MDEBUG(("\nfind trying at %ld\n", LOFF(begin))); MDEBUG(("\nfind trying at %ld\n", LOFF(begin)));
@ -493,11 +491,11 @@ cfind(struct vars *v,
int ret; int ret;
s = newdfa(v, &v->g->search, cm, &v->dfa1); s = newdfa(v, &v->g->search, cm, &v->dfa1);
NOERR(); if (s == NULL)
return v->err;
d = newdfa(v, cnfa, cm, &v->dfa2); d = newdfa(v, cnfa, cm, &v->dfa2);
if (ISERR()) if (d == NULL)
{ {
assert(d == NULL);
freedfa(s); freedfa(s);
return v->err; return v->err;
} }