Re: [BUGS] BUG #1270: stack overflow in thread in fe_getauthname - Mailing list pgsql-hackers

What do people think about using (sizeof(struct passwd) + BUFLEN/2) rather
than BUFLEN for the getpwuid_r size, or (sizeof(struct passwd) + MAXPGPATH*2)?
That would reduce the stack requirements and still be safe, I think.

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Peter Davie wrote:
> Hi Bruce,
> 
> (As I explained to Tom, the situation for me is difficult:
> 
> How can I "fix the app" when the application is a commercial binary which
> provides no means of configuring the stack size for the thread?  I have
> been successfully using PostgreSQL with this application since v7.1 and
> have a happy customer with it.  Now, upgrading the database to v7.4.5
> which is strongly recommended by the development group (due to potentially
> serious bugs) means that the application no longer works!
> )
> 
> Since then I have done some background reading
> <http://www.opengroup.org/onlinepubs/009695399/functions/getpwuid.html>:
> 
> [TSF]  The getpwuid_r() function shall update the passwd structure pointed
> to by pwd and store a pointer to that structure at the location pointed to
> by result. The structure shall contain an entry from the user database
> with a matching uid. Storage referenced by the structure is allocated from
> the memory provided with the buffer parameter, which is bufsize bytes in
> size. The maximum size needed for this buffer can be determined with the
> {_SC_GETPW_R_SIZE_MAX} sysconf() parameter. A NULL pointer shall be
> returned at the location pointed to by result on error or if the requested
> entry is not found.
> 
> On Tru64 UNIX, sysconf(_SC_GETPW_R_SIZE_MAX) returns 1024.
> 
> Thanks
> Peter
> 
> > Tom Lane wrote:
> >> Bruce Momjian <pgman@candle.pha.pa.us> writes:
> >> > Oops.  Yep, that is sloppy programming on our part, perhaps my part if
> >> I
> >> > added those.  Anyway, patch attached and applied. I used the proper
> >> > struct sizes instead of BUFSIZ.
> >>
> >> You just broke it.
> >>
> >> Those buffers are not used to hold struct passwd's, but to hold
> >> multiple character strings to which the struct passwd will point;
> >> any one of which could be long, but particularly the home directory
> >> path.
> >>
> >> My man page for getpwuid_r says that the minimum recommended buffer size
> >> is 1024.
> >>
> >> > This will be in 8.0.
> >>
> >> I think we should revert it entirely.  A small buffer size risks
> >> breaking things unnecessarily, and as I replied earlier, the request
> >> to make libpq run in a less-than-8K stack is not reasonable anyway.
> >
> > Reverted.  I forgot about the requirement to store pointers used by the
> > structure.  I knew that when doing the thread patches but forgot about
> > it.
> >
> > --
> >   Bruce Momjian                        |  http://candle.pha.pa.us
> >   pgman@candle.pha.pa.us               |  (610) 359-1001
> >   +  If your life is a hard drive,     |  13 Roberts Road
> >   +  Christ can be your backup.        |  Newtown Square, Pennsylvania
> > 19073
> >
> 
> 
> -- 
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--  Bruce Momjian                        |  http://candle.pha.pa.us pgman@candle.pha.pa.us               |  (610)
359-1001+  If your life is a hard drive,     |  13 Roberts Road +  Christ can be your backup.        |  Newtown Square,
Pennsylvania19073