Re: [PATCH] Fix out-of-bouds access (src/common/wchar.c)

Em qua., 16 de fev. de 2022 às 00:12, Kyotaro Horiguchi <
horikyota(dot)ntt(at)gmail(dot)com> escreveu:

> At Tue, 15 Feb 2022 09:17:34 -0300, Ranier Vilela <ranier(dot)vf(at)gmail(dot)com>
> wrote in
> > Per Coverity.
>
> Thanks for the source:)
>
> > Like the function pg_encoding_max_length_sql
> > (src/backend/utils/mb/mbutils.c)
> > Only assertion is insufficient to avoid accessing array out-of-bounds.
> >
> > This bug is live according Coverity at function: pg_verify_mbstr_len
> > (src/backend/utils/mb/mbutils.c)
> > CID 1469870 (#1 of 1): Out-of-bounds access (OVERRUN)7. overrun-call:
> > Overrunning
> > callee's array of size 42 by passing argument src_encoding (which
> evaluates
> > to 63) in call to pg_verify_mbstr_len. [show details
> > <
> https://scan6.scan.coverity.com/eventId=32693869-7&modelId=32693869-0&fileInstanceId=131415642&filePath=%2Fdll%2Fpostgres%2Fpostgres%2Fsrc%2Fbackend%2Futils%2Fmb%2Fmbutils.c&fileStart=1546&fileEnd=1605
> >
>
> It returns 400..
>
> > ]
> > 633 retval = pg_verify_mbstr_len(src_encoding, src_str, len,
> false);
> > 634
> >
> > Trivial patch attached.
>
> Mmm? If the assert doesn't work, there should be inconcsistency
> between pg_enc and pg_wchar_table. But AFAICS they are consistent.
>
The consistency is between pg_encname_tbl and pc_enc, and AFAICS are
consistent.

>
> The patch:
> pg_encoding_max_length(int encoding)
> {
> - Assert(PG_VALID_ENCODING(encoding));
> -
> - return pg_wchar_table[encoding].maxmblen;
> + if (PG_VALID_ENCODING(encoding))
> + return pg_wchar_table[encoding].maxmblen;
> + else
> + return -1;
>
> Returning -1 for invalid encoding is, I think, flat wrong.
>
Ok, if -1 is wrong, what should the value of return if
somebody calling this function like:
pg_encoding_max_length(63);

Of course, with patch applied, because with original code
has memory corruption, if built and run without DEBUG.

regards,
Ranier Vilela