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References: <20240320182607.1472887-1-jcmvbkbc@gmail.com> <202403211004.19F5EE27F@keescook>
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From: Max Filippov <jcmvbkbc@gmail.com>
Date: Fri, 22 Mar 2024 09:39:43 -0700
Message-ID: <CAMo8BfKhk8dk3-n7gx3edZKSZUhCa+GJf4XwFvXr6bYzcwsb-A@mail.gmail.com>
Subject: Re: [PATCH] exec: fix linux_binprm::exec in transfer_args_to_stack()
To: Kees Cook <keescook@chromium.org>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, 
	linux-fsdevel@vger.kernel.org, Eric Biederman <ebiederm@xmission.com>, 
	Alexander Viro <viro@zeniv.linux.org.uk>, Christian Brauner <brauner@kernel.org>, Jan Kara <jack@suse.cz>, 
	Rich Felker <dalias@libc.org>, stable@vger.kernel.org
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On Thu, Mar 21, 2024 at 8:48=E2=80=AFPM Kees Cook <keescook@chromium.org> w=
rote:
> On Thu, Mar 21, 2024 at 12:52:16PM -0700, Max Filippov wrote:
> > On Thu, Mar 21, 2024 at 10:05=E2=80=AFAM Kees Cook <keescook@chromium.o=
rg> wrote:
> > > What's the best way to test this? (Is there a qemu setup I can use to
> > > see the before/after of AT_EXECFN?)
> >
> > I put a readme with the steps to build such system here:
> >   http://jcmvbkbc.org/~dumb/tmp/202403211236/README
> > it uses a prebuilt rootfs image and a 6.8 kernel branch with two
> > patches on top of it: one adds a dts and a defconfig and the other
> > is this fix. The rootfs boots successfully with this fix, but panics
> > if this fix is removed.
>
> Does musl have something like the LD_SHOW_AUXV env variable. With glibc,
> I usually explore auxv like so:
>
> $ LD_SHOW_AUXV=3D1 uname -a | grep EXECFN
> AT_EXECFN:            /usr/bin/uname

I couldn't find anything like that in either musl or uClibc-ng.
So I updated the above rootfs and put the following program
into it as /bin/test-auxv:

#include <stdio.h>
#include <sys/auxv.h>

int main()
{
       unsigned long p =3D getauxval(AT_EXECFN);
       fprintf(stderr, "AT_EXECFN: 0x%lx\n", p);
       if (p)
               fprintf(stderr, "%s\n", (const char *)p);
       return 0;
}

While looking at it I also noticed that /proc/<pid>/auxv is empty
on NOMMU, looks like there will be yet another fix for that.

--=20
Thanks.
-- Max