Re: [PATCH] binfmt_elf: Do not move brk for INTERP-less ET_EXEC

[Richard Kojedzinszky]

Hi,

Thanks for the fix, again. I am not familiar with the code here, I 
suspect the intent was to fix or improve something. That happens 
sometimes, that things get broken. I am happy that I could report it, 
and it got fixed quickly.

Thanks again,
Richard


2019-09-26 20:37 idÅpontban Kees Cook ezt Ãrta:
> On Thu, Sep 26, 2019 at 08:26:12PM +0200, Richard Kojedzinszky wrote:
> > Thanks for the quick patch. It seems my binaries start up well, and 
> > work as
> > expected, as before.
> >
> > Thanks again for the quick response.
>
> Awesome; thanks for the testing (and sorry for the breakage)! :)
>
> -Kees
>
> > Regards,
> > Richard Kojedzinszky
> >
> > 2019-09-26 19:15 idÅpontban Kees Cook ezt Ãrta:
> > > When brk was moved for binaries without an interpreter, it should have
> > > been limited to ET_DYN only. In other words, the special case was an
> > > ET_DYN that lacks an INTERP, not just an executable that lacks INTERP.
> > > The bug manifested for giant static executables, where the brk would end
> > > up in the middle of the text area on 32-bit architectures.
> > >
> > > Reported-by: Richard Kojedzinszky <richard@xxxxxxxxx>
> > > Fixes: bbdc6076d2e5 ("binfmt_elf: move brk out of mmap when doing
> > > direct loader exec")
> > > Cc: stable@xxxxxxxxxxxxxxx
> > > Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> > > ---
> > > Richard, are you able to test this? I'm able to run the gitea binary
> > > with this change, and my INTERP-less ET_DYN tests (from the original
> > > bug) continue to pass as well.
> > > ---
> > >  fs/binfmt_elf.c | 3 ++-
> > >  1 file changed, 2 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
> > > index cec3b4146440..ad4c6b1d5074 100644
> > > --- a/fs/binfmt_elf.c
> > > +++ b/fs/binfmt_elf.c
> > > @@ -1121,7 +1121,8 @@ static int load_elf_binary(struct linux_binprm
> > > *bprm)
> > >  		 * (since it grows up, and may collide early with the stack
> > >  		 * growing down), and into the unused ELF_ET_DYN_BASE region.
> > >  		 */
> > > -		if (IS_ENABLED(CONFIG_ARCH_HAS_ELF_RANDOMIZE) && !interpreter)
> > > +		if (IS_ENABLED(CONFIG_ARCH_HAS_ELF_RANDOMIZE) &&
> > > +		    loc->elf_ex.e_type == ET_DYN && !interpreter)
> > >  			current->mm->brk = current->mm->start_brk =
> > >  				ELF_ET_DYN_BASE;
> > >
> > > --
> > > 2.17.1