libpq: fix unlikely memory leak

The attached patch fixes a theoretical memory leak in libpq: if the
second malloc() fails due to OOM, the memory returned by the first
(successful) malloc() will be leaked.

Barring any objections I'll apply this tomorrow.

Per report from EnterpriseDB's Coverity analysis.

-Neil

Neil Conway <neilc(at)samurai(dot)com> writes:
> The attached patch fixes a theoretical memory leak in libpq: if the
> second malloc() fails due to OOM, the memory returned by the first
> (successful) malloc() will be leaked.

Since both allocations are only transient within this routine, there's
a simpler more effective solution, which is to only do one malloc in
the first place:

char *crypt_pwd2;

/* need enough space for 2 MD5 hashes */
if (!(crypt_pwd = malloc(2 * (MD5_PASSWD_LEN + 1))))
{
fprintf(stderr, libpq_gettext("out of memory\n"));
return STATUS_ERROR;
}
crypt_pwd2 = crypt_pwd + (MD5_PASSWD_LEN + 1);

and drop the free(crypt_pwd2) calls.

regards, tom lane

Tom Lane wrote:
> Since both allocations are only transient within this routine, there's
> a simpler more effective solution, which is to only do one malloc in
> the first place

Yeah, true. Attached is a revised patch -- committed to HEAD.

-Neil