Re: [PATCH] exec: fix linux_binprm::exec in transfer_args_to_stack()

Kees Cook
2024-03-21T17:05:03Z

On Wed, Mar 20, 2024 at 11:26:07AM -0700, Max Filippov wrote:
> In NUMMU kernel the value of linux_binprm::p is the offset inside the
> temporary program arguments array maintained in separate pages in the
> linux_binprm::page. linux_binprm::exec being a copy of linux_binprm::p
> thus must be adjusted when that array is copied to the user stack.
> Without that adjustment the value passed by the NOMMU kernel to the ELF
> program in the AT_EXECFN entry of the aux array doesn't make any sense
> and it may break programs that try to access memory pointed to by that
> entry.
>
> Adjust linux_binprm::exec before the successful return from the
> transfer_args_to_stack().

What's the best way to test this? (Is there a qemu setup I can use to
see the before/after of AT_EXECFN?)

How did you encounter the problem?

>
> Cc: stable@vger.kernel.org
> Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
> ---
> fs/exec.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/fs/exec.c b/fs/exec.c
> index af4fbb61cd53..5ee2545c3e18 100644
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -895,6 +895,7 @@ int transfer_args_to_stack(struct linux_binprm *bprm,
> goto out;
> }
>
> + bprm->exec += *sp_location - MAX_ARG_PAGES * PAGE_SIZE;
> *sp_location = sp;
>
> out:
> --
> 2.39.2
>

--
Kees Cook