Re: failed reading "Smallest x86 ELF Hello World"

[Mark Wielaard <mark at klomp dot org>]

On Wed, 2017-10-04 at 20:55 +0200, Mark Wielaard wrote:
> The first issue is indeed that almost anything that goes wrong when
> setting up the initial Elf handle ends up being described as
> ELF_E_INVALID_FILE. Which is not always the correct error code. So I
> introduced ELF_E_INVALID_ELF which indicates it is bad ELF data being
> encountered and not just the inability to read the data from the file
> descriptor. Also in a couple of cases we didn't explicitly set the
> libelf errno to indicate what really went wrong. I made sure we
> always
> do now.
> 
>   libelf: Add ELF_E_INVALID_ELF error value.
>
> [...]
>
> But while auditing this code it is clear we go out of our way to get
> the section (count) making sure we don't touch any bad data. If there
> is a change we might read anything bad from the (mmapped) file then
> we
> explicitly set the elf->state.elf[64|32].scns.cnt to zero. Which is
> respected throughout libelf whenever we try to touch section headers.
> Except... during the initial read we double check e_shoff is sane and
> error out early. Even though the code right below it explicitly
> doesn't
> use it when scncnt is zero. So we can fix this sanity check.
> 
>   libelf: Don't error out when sanity checking e_shoff if scncnt is
> zero.

I pushed both these commits to master now.

Cheers,

Mark