Re: fix for palloc() of user-supplied length

Hello again,

*any* comment on this at all?

thanks,
-s

----- Original Message -----
From: "Serguei Mokhov" <sa_mokho(at)alcor(dot)concordia(dot)ca>
Sent: September 02, 2002 4:11 AM

> Hello,
>
> ----- Original Message -----
> From: "Bruce Momjian" <pgman(at)candle(dot)pha(dot)pa(dot)us>
> Sent: September 02, 2002 1:05 AM
>
> > Would someone submit a patch for this?
>
> Attached please find an attempt to fix the volunerability issue below.
>
> Affected files are:
>
> /src/include/libpq/libpq.h
> /src/include/libpq/pqformat.h
> /src/backend/libpq/pqformat.c
> /src/backend/libpq/pqcomm.c
> /src/backend/libpq/auth.c
>
> "Briefly" the changes:
>
> Main victims for the change were pq_getstring() and pq_getstr()
> (which calls the former) in pqformat.c and pqcomm.c. pq_getstring() is the one reading
> until \0 and might possibly render the system run out of memory.
>
> Changing pq_getstring() alone would break a lot code, so I
> added a two more functions: pq_getstring_common() and
> pq_getstring_bounded(). The former is a big part of what used to be
> pq_getstring() and the latter is a copy of the new pq_getstring()
> with the string length check. Creating pq_getstring_common()
> was suggested by its reuse in pq_getstring() and pq_getstring_bounded()
> avoiding code duplication.
>
> Similar changes were done for pq_getstr(). Its common code converting
> to MULTIBYTE was placed in pq_getstr_multibyte() and pq_getstr() and
> (newly added) pq_getstr_bounded() both call it before returning a result.
>
> WRT above, two places in auth.c were changed to call pq_getstr_bounded()
> instead of pq_getstr() on password read. I'm not sure if
> there are other places where that might be needed...
>
> Might look ugly for some, but looks like a not-so-bad solution
> to me. If I'm completely wrong, I'd like to have some guidance then :)
> Please review with care. I'm off to bed.
>
> Thanks,
> -s
>
> PS: The patch also fixes a typo in the be-secure.c comment :)
>
> > Tom Lane wrote:
> > > Neil Conway <neilc(at)samurai(dot)com> writes:
> > > > (2) The length supplied by the user is completely ignored by
> > > > the code, and it simply reads the input until it sees a
> > > > NULL terminator (read the comments in the code about 10
> > > > lines down.) Therefore, any sanity checking on the length
> > > > specified by the user is a waste of time.
> > >
> > > Agreed; the fact that the protocol requires a length word at all is just
> > > a hangover from the past. We can read the length word and forget it.
> > >
> > > I wonder though if it'd be worthwhile to limit the length of the string
> > > that we are willing to read from the client in the second step. We are
> > > at this point dealing with an unauthenticated user, so we should be
> > > untrusting. And I think Sir Mordred has a point: forcing a backend to
> > > allocate a lot of memory can be a form of DoS attack.
> > >
> > > regards, tom lane