Re: [Xen-devel] [PATCH v6 08/24] xsplice: Add helper elf routines

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 09.04.16 at 00:10, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 08/04/16 22:26, Konrad Rzeszutek Wilk wrote:
>> On Fri, Apr 08, 2016 at 03:53:44PM +0100, Andrew Cooper wrote:
>>> On 07/04/16 04:49, Konrad Rzeszutek Wilk wrote:
>>>> +    nsym = symtab_sec->sec->sh_size / symtab_sec->sec->sh_entsize;
>>> Has anything checked sh_entsize for being 0 or -1 ?
>> Let me double-check.
> 
> Git grep says elf_resolve_sections() has
> 
>     if ( !elf->symtab->sec->sh_size ||
>          elf->symtab->sec->sh_entsize < sizeof(Elf_Sym) )
>     {
>         dprintk(XENLOG_DEBUG, XSPLICE "%s: Symbol table header is 
> corrupted!\n",
>                 elf->name);
>         return -EINVAL;
>     }
> 
> I would check for !=, rather than <
> 
> Nothing good can come of having sh_entsize being bigger than what we
> expect an Elf_Sym to be.

The whole purpose of recording the section table entry size is such
that the structure could eventually get extended without breaking
existing consumers. Hence != is not what the standard suggests to
be used.

> Also be aware that Elf_Sym.sh_entsize and Ehdr.e_shentsize appear to be
> multiple locations containing the same information.  I would also cross
> check them.

You mean Elf_Section.sh_entsize, which has a completely different
purpose (see e.g. relocation sections).

Jan


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel