From: Peter Chang <weasel@cs.stanford.edu>
To: linuxppc-dev@lists.linuxppc.org
Subject: Re: dl-load.c (ld.so) bug??
Date: Mon, 21 Jun 1999 21:36:58 -0700 [thread overview]
Message-ID: <v04205405b394c1fe1645@[209.239.164.131]> (raw)
In-Reply-To: <19990621230921.A20471@drow.res.cmu.edu>
At 23:09 -0400 06.21.1999, Daniel Jacobowitz wrote:
>On Mon, Jun 21, 1999 at 10:48:12PM -0400, Hollis R Blanchard wrote:
> >
> > > No. Electric Fence is designed to catch programming errors, such as
> > > attempting to access memory which was not 'malloc'ed. I have traced this
> > > down extensively a couple of months ago, and found that it does indeed
> > > appear to overrun what it malloced.
> >
> > I have two even simpler test cases for you:
> >
> > int main(void){
> > char *ptr=NULL;
> > free(ptr);
> > }
>
>Well, that one would probably segfault anyway (or at least, is not
>guaranteed not to).
Hmm... the docs taht I have say this:
2 The free function causes the space pointed to by ptr to be
deallocated, that is, made
available for further allocation. If ptr is a null pointer, no action
occurs. Otherwise, if
the argument does not match a pointer earlier returned by the calloc, malloc,or
realloc function, or if the space has been deallocated by a call to
free or realloc,
the behavior is undefined.
> > int main(void){
> > char *ptr = (char *)malloc(100);
> > }
>
>That one's a problem, though :)
Why? Its allocating memory, but never freeing it. Its a leak, but not
accessing things out of bounds. I haven't used ElectricFence, but its
not going to catch a bounds error on this.
> > If this were the case, wouldn't you expect ridiculous levels of
>instability?
>
>Depends entirely on what it overwrote.
Especially, if the malloc (like most) was sub-allocating from an os
allocated block. In this case it might be possible that the block
after the overwritten block was not holding any valid data or at
least wasn't ever given out by malloc/calloc/realloc.
\p
---
sed quis custodiet ipsos custodes
--Juvenal *Satire* VI, 165
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next prev parent reply other threads:[~1999-06-22 4:36 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
1999-06-21 22:52 dl-load.c (ld.so) bug?? Troy Benjegerdes
1999-06-22 0:04 ` Hollis R Blanchard
1999-06-22 1:57 ` Troy Benjegerdes
1999-06-22 2:48 ` Hollis R Blanchard
1999-06-22 3:09 ` Daniel Jacobowitz
1999-06-22 4:36 ` Peter Chang [this message]
1999-06-22 13:52 ` Hollis R Blanchard
[not found] <Pine.LNX.3.96L.990622003119.5237E-100000@unix47.andrew.cmu.edu>
1999-06-22 4:39 ` Peter Chang
[not found] <199906231258.HAA25989@www.cedarnet.org>
1999-06-23 13:17 ` Geert Uytterhoeven
1999-06-23 14:19 ` Hollis R Blanchard
1999-06-23 14:32 ` Kevin Puetz
[not found] <Pine.LNX.4.04.9906211749280.27642-100000@narn.local.drgw.n et>
1999-06-23 14:37 ` Franz Sirl
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