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Re: Teaching C (was Re: hexump.c)

From Nobody <nobody@nowhere.com>
Subject Re: Teaching C (was Re: hexump.c)
Date 2011-09-14 22:20 +0100
Message-Id <pan.2011.09.14.21.20.17.797000@nowhere.com>
Newsgroups comp.lang.c
References <j4ducg$lmn$1@speranza.aioe.org> <pan.2011.09.14.12.31.49.174000@nowhere.com> <j4qa4f$4hh$1@speranza.aioe.org> <lnpqj2amz7.fsf@nuthaus.mib.org> <j4r4in$pv2$1@speranza.aioe.org>
Organization Zen Internet

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On Wed, 14 Sep 2011 20:59:03 +0000, Alan Curry wrote:

> I've just done this test on several programs. There were many segfaults.
> Several print an angry message about argv[0] being NULL and then abort!
> It seems to be a "you know exactly what you did and you should be
> ashamed of yourself" type of error.
> 
> Most disturbing are the many setuid programs that segfaulted, including
> passwd, mount, and su.

This isn't necessarily problematic. It's important that setuid programs
consider the security implications, but (intentionally) terminating on
SIGSEGV isn't inherently worse than terminating on SIGABRT (i.e.
explicitly calling abort()).

Where it does become a problem is if a program blindly dereferences
argv[0] when it has gotten itself into a position where it /needs/ to
perform clean-up (e.g. once it has created a lock file).

I've seen one setuid program where the startup sequence involved a long
sequence of sanity checks, and any failure would result in an immediate
_exit(). It wouldn't even risk trying to report errors until the sanity
checks were complete.

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Thread

hexump.c jacob navia <jacob@spamsink.net> - 2011-09-09 22:53 +0200
  Re: hexump.c tea strainer <nospam@nospam.com> - 2011-09-09 21:06 +0000
    Re: hexump.c jacob navia <jacob@spamsink.net> - 2011-09-09 23:57 +0200
    Re: hexump.c NicStevens <nic.stevens@gmail.com> - 2011-09-12 13:22 -0700
  Re: hexump.c Ian Collins <ian-news@hotmail.com> - 2011-09-10 09:18 +1200
    Re: hexump.c jacob navia <jacob@spamsink.net> - 2011-09-09 23:59 +0200
  Re: hexump.c Ike Naar <ike@iceland.freeshell.org> - 2011-09-09 22:29 +0000
    Re: hexump.c jacob navia <jacob@spamsink.net> - 2011-09-10 00:39 +0200
      Re: hexump.c Ike Naar <ike@iceland.freeshell.org> - 2011-09-09 22:53 +0000
        Re: hexump.c jacob navia <jacob@spamsink.net> - 2011-09-10 00:58 +0200
        Re: hexump.c Seebs <usenet-nospam@seebs.net> - 2011-09-13 06:44 +0000
          Re: hexump.c jacob navia <jacob@spamsink.net> - 2011-09-13 10:33 +0200
            Re: hexump.c Fritz Wuehler <fritz@spamexpire-201109.rodent.frell.theremailer.net> - 2011-09-13 18:02 +0200
            Teaching C (was Re: hexump.c) Kenneth Brody <kenbrody@spamcop.net> - 2011-09-13 16:36 -0400
              Re: Teaching C (was Re: hexump.c) jacob navia <jacob@spamsink.net> - 2011-09-13 22:44 +0200
                Re: Teaching C (was Re: hexump.c) Nobody <nobody@nowhere.com> - 2011-09-14 13:31 +0100
                Re: Teaching C (was Re: hexump.c) jacob navia <jacob@spamsink.net> - 2011-09-14 15:27 +0200
                Re: Teaching C (was Re: hexump.c) Richard Damon <news.x.richarddamon@xoxy.net> - 2011-09-14 11:49 -0400
                Re: Teaching C (was Re: hexump.c) Keith Thompson <kst-u@mib.org> - 2011-09-14 13:27 -0700
                Re: Teaching C (was Re: hexump.c) pacman@kosh.dhis.org (Alan Curry) - 2011-09-14 20:59 +0000
                Re: Teaching C (was Re: hexump.c) Nobody <nobody@nowhere.com> - 2011-09-14 22:20 +0100
                Re: Teaching C (was Re: hexump.c) James Kuyper <jameskuyper@verizon.net> - 2011-09-14 17:20 -0400
                Re: Teaching C (was Re: hexump.c) pacman@kosh.dhis.org (Alan Curry) - 2011-09-15 01:51 +0000
                Re: Teaching C (was Re: hexump.c) Keith Thompson <kst-u@mib.org> - 2011-09-14 19:29 -0700
                Re: Teaching C (was Re: hexump.c) Keith Thompson <kst-u@mib.org> - 2011-09-14 19:21 -0700
                Re: Teaching C Ben Pfaff <blp@cs.stanford.edu> - 2011-09-14 19:58 -0700
                Re: Teaching C Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2011-09-14 21:55 -0600
                Re: Teaching C James Kuyper <jameskuyper@verizon.net> - 2011-09-15 06:54 -0400
                Re: Teaching C Keith Thompson <kst-u@mib.org> - 2011-09-15 11:58 -0700
                Re: Teaching C Tim Rentsch <txr@alumni.caltech.edu> - 2012-01-24 12:57 -0800
                Re: Teaching C Nobody <nobody@nowhere.com> - 2011-09-15 14:25 +0100
                Re: Teaching C Seebs <usenet-nospam@seebs.net> - 2011-09-16 22:00 +0000
                Re: Teaching C (was Re: hexump.c) Kenneth Brody <kenbrody@spamcop.net> - 2011-09-14 12:54 -0400
                Re: Teaching C (was Re: hexump.c) James Kuyper <jameskuyper@verizon.net> - 2011-09-14 13:26 -0400
                Re: Teaching C (was Re: hexump.c) jacob navia <jacob@spamsink.net> - 2011-09-14 19:33 +0200
                Re: Teaching C (was Re: hexump.c) jameskuyper <jameskuyper@verizon.net> - 2011-09-14 11:33 -0700
                Re: Teaching C (was Re: hexump.c) jacob navia <jacob@spamsink.net> - 2011-09-14 21:17 +0200
                Re: Teaching C (was Re: hexump.c) Kenneth Brody <kenbrody@spamcop.net> - 2011-09-16 11:47 -0400
                Re: Teaching C (was Re: hexump.c) Seebs <usenet-nospam@seebs.net> - 2011-09-14 20:43 +0000
                Re: Teaching C (was Re: hexump.c) Nobody <nobody@nowhere.com> - 2011-09-14 22:35 +0100
                Re: Teaching C (was Re: hexump.c) gordonb.8a7i1@burditt.org (Gordon Burditt) - 2011-09-14 17:31 -0500
                Re: Teaching C (was Re: hexump.c) jacob navia <jacob@spamsink.net> - 2011-09-14 19:32 +0200
                Re: Teaching C (was Re: hexump.c) Kenneth Brody <kenbrody@spamcop.net> - 2011-09-16 11:27 -0400
                Re: Teaching C (was Re: hexump.c) Malcolm McLean <malcolm.mclean5@btinternet.com> - 2011-09-16 08:49 -0700
                Re: Teaching C (was Re: hexump.c) James Kuyper <jameskuyper@verizon.net> - 2011-09-17 15:04 -0400
            Re: hexump.c Keith Thompson <kst-u@mib.org> - 2011-09-13 20:31 -0700
              Re: hexump.c Malcolm McLean <malcolm.mclean5@btinternet.com> - 2011-09-14 03:22 -0700
              Re: hexump.c "BartC" <bc@freeuk.com> - 2011-09-14 11:40 +0100
                Re: hexump.c jacob navia <jacob@spamsink.net> - 2011-09-14 13:54 +0200
                Re: hexump.c Nobody <nobody@nowhere.com> - 2011-09-14 13:50 +0100
                Re: hexump.c Keith Thompson <kst-u@mib.org> - 2011-09-14 11:35 -0700
                Re: hexump.c Seebs <usenet-nospam@seebs.net> - 2011-09-14 19:12 +0000
                Re: hexump.c John Bode <jfbode1029@gmail.com> - 2011-09-14 15:31 -0700
                Re: hexump.c jacob navia <jacob@spamsink.net> - 2011-09-15 00:59 +0200
                Re: hexump.c Kleuskes & Moos <kleuske@somewhere.else.net> - 2011-09-14 23:14 +0000
                Re: hexump.c John Bode <jfbode1029@gmail.com> - 2011-09-15 08:52 -0700
                Re: hexump.c Jens Gustedt <jens.gustedt@loria.fr> - 2011-09-14 21:22 +0200
                Re: hexump.c jacob navia <jacob@spamsink.net> - 2011-09-14 21:26 +0200
                Re: hexump.c Ian Collins <ian-news@hotmail.com> - 2011-09-15 07:32 +1200
                Re: hexump.c jacob navia <jacob@spamsink.net> - 2011-09-14 21:44 +0200
                Re: hexump.c Keith Thompson <kst-u@mib.org> - 2011-09-14 13:49 -0700
                Re: hexump.c Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2011-09-16 00:50 +0300
                Re: hexump.c Keith Thompson <kst-u@mib.org> - 2011-09-15 18:34 -0700
                Re: hexump.c Keith Thompson <kst-u@mib.org> - 2011-09-14 12:16 -0700
                Hypocrites jacob navia <jacob@spamsink.net> - 2011-09-14 21:40 +0200
                Re: Hypocrites Keith Thompson <kst-u@mib.org> - 2011-09-14 19:11 -0700
                Re: hexump.c Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-09-14 15:05 +0100
                Re: hexump.c Malcolm McLean <malcolm.mclean5@btinternet.com> - 2011-09-14 07:56 -0700
                Re: hexump.c "BartC" <bc@freeuk.com> - 2011-09-14 17:23 +0100
              Re: hexump.c Seebs <usenet-nospam@seebs.net> - 2011-09-14 19:12 +0000
              Re: hexump.c John Bode <jfbode1029@gmail.com> - 2011-09-14 15:24 -0700
      Re: hexump.c gordonb.ik17p@burditt.org (Gordon Burditt) - 2011-09-09 18:16 -0500
        Re: hexump.c Jorgen Grahn <grahn+nntp@snipabacken.se> - 2011-09-12 22:24 +0000
  Re: hexump.c "Morris Keesan" <mkeesan@post.harvard.edu> - 2011-09-09 20:33 -0400
    Re: hexump.c Ian Collins <ian-news@hotmail.com> - 2011-09-10 12:42 +1200
      Re: hexump.c "Morris Keesan" <mkeesan@post.harvard.edu> - 2011-09-10 17:16 -0400
    Re: hexump.c jacob navia <jacob@spamsink.net> - 2011-09-10 10:03 +0200
  Re: hexump.c Nobody <nobody@nowhere.com> - 2011-09-10 10:04 +0100
    Re: hexump.c jacob navia <jacob@spamsink.net> - 2011-09-10 11:41 +0200
      Re: hexump.c pete <pfiland@mindspring.com> - 2011-09-10 05:51 -0400
        Re: hexump.c jacob navia <jacob@spamsink.net> - 2011-09-10 12:38 +0200
          Re: hexump.c Nobody <nobody@nowhere.com> - 2011-09-10 17:53 +0100
  Re: hexump.c jacob navia <jacob@spamsink.net> - 2011-09-10 12:46 +0200
    Re: hexump.c Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-09-10 13:03 +0100
      Re: hexump.c jacob navia <jacob@spamsink.net> - 2011-09-10 15:34 +0200
    Re: hexump.c "Morris Keesan" <mkeesan@post.harvard.edu> - 2011-09-10 17:37 -0400
      Re: hexump.c jacob navia <jacob@spamsink.net> - 2011-09-11 00:10 +0200
        Re: hexump.c Patrick Scheible <kkt@zipcon.net> - 2011-09-10 21:03 -0700
  Re: hexump.c Barry Schwarz <schwarz45@yahoo.com> - 2011-09-11 00:37 -0700
    Re: hexump.c jacob navia <jacob@spamsink.net> - 2011-09-11 13:56 +0200

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