linux-hardening - Re: [PATCH v3 0/4] binfmt_elf: Support segments with 0 filesz and misaligned starts

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Date: Wed, 27 Sep 2023 15:25:21 -0500
From: "Eric W. Biederman" <ebiederm@...ssion.com>
To: Kees Cook <keescook@...omium.org>
Cc: Sebastian Ott <sebott@...hat.com>,  Thomas Weißschuh
 <linux@...ssschuh.net>,  Al Viro <viro@...iv.linux.org.uk>,  Christian
 Brauner <brauner@...nel.org>,  Pedro Falcato <pedro.falcato@...il.com>,
  linux-kernel@...r.kernel.org,  linux-fsdevel@...r.kernel.org,
  linux-mm@...ck.org,  linux-hardening@...r.kernel.org
Subject: Re: [PATCH v3 0/4] binfmt_elf: Support segments with 0 filesz and
 misaligned starts

Kees Cook <keescook@...omium.org> writes:

> Hi,
>
> This is the continuation of the work Eric started for handling
> "p_memsz > p_filesz" in arbitrary segments (rather than just the last,
> BSS, segment). I've added the suggested changes:
>
>  - drop unused "elf_bss" variable
>  - report padzero() errors when PROT_WRITE is present
>  - refactor load_elf_interp() to use elf_load()
>
> This passes my quick smoke tests, but I'm still trying to construct some
> more complete tests...

Acked-by: "Eric W. Biederman" <ebiederm@...ssion.com>

You might also consider using elf_load in load_elf_library.

The code in load_elf_library only supports files with a single program
header, and I think is only needed for libc5.

The advantage is that load_elf_library would be using well tested code,
vm_brk would have no callers, and padzero would only be called by
elf_load, and load_elf_library would do little more than just call
load_elf_library.

Eric

>
> -Kees
>
> Eric W. Biederman (1):
>   binfmt_elf: Support segments with 0 filesz and misaligned starts
>
> Kees Cook (3):
>   binfmt_elf: elf_bss no longer used by load_elf_binary()
>   binfmt_elf: Provide prot bits as context for padzero() errors
>   binfmt_elf: Use elf_load() for interpreter
>
>  fs/binfmt_elf.c | 192 ++++++++++++++++++------------------------------
>  1 file changed, 71 insertions(+), 121 deletions(-)