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

[Richard Kojedzinszky]

Hi Kees,

Thanks for the quick patch. It seems my binaries start up well, and work 
as expected, as before.

Thanks again for the quick response.

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