Re: Printing backtrace of postgres processes

On Sun, Nov 22, 2020 at 11:55 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>
> vignesh C <vignesh21@gmail.com> writes:
> > The idea here is to implement & expose pg_print_callstack function,
> > internally what this function does is, the connected backend will send
> > SIGUSR1 signal by setting PMSIGNAL_BACKTRACE_EMIT to the postmaster
> > process. Postmaster process will send a SIGUSR1 signal to the process
> > by setting PROCSIG_BACKTRACE_PRINT if the process has access to
> > ProcSignal. As syslogger process & Stats process don't have access to
> > ProcSignal, multiplexing with SIGUSR1 is not possible for these
> > processes, hence SIGUSR2 signal will be sent for these processes. Once
> > the process receives this signal it will log the backtrace of the
> > process.
>
> Surely this is *utterly* unsafe.  You can't do that sort of stuff in
> a signal handler.
>
> It might be all right to set a flag that would cause the next
> CHECK_FOR_INTERRUPTS to print a backtrace, but I'm not sure
> how useful that really is.
>
> The proposed postmaster.c addition seems quite useless, as there
> is exactly one stack trace it could ever log.
>
> I would like to see some discussion of the security implications
> of such a feature, as well.  ("There aren't any" is the wrong
> answer.)

Hi Hackers,

Any thoughts on the security implication for this feature.

Regards,
Vignesh
EnterpriseDB: http://www.enterprisedb.com