Re: readelf [PATCH]

[Sergei Pachkov]

short example whith readelf binary.
The readelf version is 2.13.90 (20021009).

with hexedit open readelf and go to 0x21 position in file.
replace value, 0x61 in my case, with 0xFF and save file.
after little destroy in elf header try launch normal, not changed 
readelf, with option '-a /tmp/readelf'
and see some errors, segfaults and mistakes.

Some programmers try to hide information about section in their 
programms in that way.


Nick Clifton wrote:

> Hi Sergei,
>
>  
>
> > I have found a little bug in "readelf" this weekend.  Sometimes
> > variable called "process_headers" may have NULL value
> >    
>
> err you mean 'section_headers'
>
>  
>
> > and reading its members would fail.  For avoid this problem I have
> > wrote little patch.  In the patch I have add few checks of variable
> > process_headers like this: 
> > if (process_headers != NULL)
> > or
> > if (process_headers == NULL)
> >    
>
> This should not be necessary.  The functions that initialise
> section_headers (either get_32bit_section_headers or
> get_64bit_section_headers) should always return an error code if they
> failed, and this should always be checked.  So the correct fix for the
> bug is to find out where get_{32|64}bit_section_headers() is not
> returning an error code, or where their return values are being
> ignored and to fix these places.
>
> How did you cause readelf to attempt to use section_headers when it
> was not initialised ?
>
>  
>
> > {
> >   PTR mvar;
> > -
> > +  int err;
> > +  int c;
> > +  
> >   if (size == 0)
> >     return NULL;
> >
> > -  if (fseek (file, offset, SEEK_SET))
> > +  err = fseek (file, offset, SEEK_SET);
> > +  Ó = getc(file);
> > +
> > +  if ((Ó == EOF) || (err != 0))
> >    
>
> Note - this appears to be a fix/hack for a completely unrelated
> problem and should not have been included in this patch.
>
> Cheers
>        Nick
>
>
>