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From:   "Eric W. Biederman" <ebiederm@xmission.com>
To:     Kees Cook <keescook@chromium.org>
Cc:     Sebastian Ott <sebott@redhat.com>,
        Thomas =?utf-8?Q?Wei=C3=9Fschuh?= <linux@weissschuh.net>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Christian Brauner <brauner@kernel.org>,
        Pedro Falcato <pedro.falcato@gmail.com>,
        linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-mm@kvack.org, linux-hardening@vger.kernel.org
References: <20230927033634.make.602-kees@kernel.org>
Date:   Wed, 27 Sep 2023 15:25:21 -0500
In-Reply-To: <20230927033634.make.602-kees@kernel.org> (Kees Cook's message of
        "Tue, 26 Sep 2023 20:42:17 -0700")
Message-ID: <87il7v8itq.fsf@email.froward.int.ebiederm.org>
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Subject: Re: [PATCH v3 0/4] binfmt_elf: Support segments with 0 filesz and
 misaligned starts
Precedence: bulk

Kees Cook <keescook@chromium.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@xmission.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(-)