From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann Subject: Re: [PATCH] binfmt_flat: make load_flat_shared_library() work Date: Wed, 29 May 2019 14:05:21 +0200 Message-ID: References: <20190524201817.16509-1-jannh@google.com> <20190525144304.e2b9475a18a1f78a964c5640@linux-foundation.org> <6956cfe5-90d4-aad4-48e3-66b0ece91fed@linux-m68k.org> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Return-path: In-Reply-To: <6956cfe5-90d4-aad4-48e3-66b0ece91fed@linux-m68k.org> Sender: linux-kernel-owner@vger.kernel.org To: Greg Ungerer Cc: Jann Horn , Andrew Morton , Alexander Viro , linux-fsdevel , kernel list , Kees Cook , Nicolas Pitre , Geert Uytterhoeven , Linux/m68k , Russell King , Linux ARM , Sergei Poselenov List-Id: linux-m68k@vger.kernel.org On Tue, May 28, 2019 at 12:56 PM Greg Ungerer wrote: > On 27/5/19 11:38 pm, Jann Horn wrote: > > On Sat, May 25, 2019 at 11:43 PM Andrew Morton > > wrote: > >> On Fri, 24 May 2019 22:18:17 +0200 Jann Horn wrote: > >>> load_flat_shared_library() is broken: It only calls load_flat_file() if > >>> prepare_binprm() returns zero, but prepare_binprm() returns the number of > >>> bytes read - so this only happens if the file is empty. > >> > >> ouch. > >> > >>> Instead, call into load_flat_file() if the number of bytes read is > >>> non-negative. (Even if the number of bytes is zero - in that case, > >>> load_flat_file() will see nullbytes and return a nice -ENOEXEC.) > >>> > >>> In addition, remove the code related to bprm creds and stop using > >>> prepare_binprm() - this code is loading a library, not a main executable, > >>> and it only actually uses the members "buf", "file" and "filename" of the > >>> linux_binprm struct. Instead, call kernel_read() directly. > >>> > >>> Cc: stable@vger.kernel.org > >>> Fixes: 287980e49ffc ("remove lots of IS_ERR_VALUE abuses") > >>> Signed-off-by: Jann Horn > >>> --- > >>> I only found the bug by looking at the code, I have not verified its > >>> existence at runtime. > >>> Also, this patch is compile-tested only. > >>> It would be nice if someone who works with nommu Linux could have a > >>> look at this patch. > >> > >> 287980e49ffc was three years ago! Has it really been broken for all > >> that time? If so, it seems a good source of freed disk space... > > > > Maybe... but I didn't want to rip it out without having one of the > > maintainers confirm that this really isn't likely to be used anymore. > > I have not used shared libraries on m68k non-mmu setups for > a very long time. At least 10 years I would think. I think Emcraft have a significant customer base running ARM NOMMU Linux, I wonder whether they would have run into this (adding Sergei to Cc). My suspicion is that they use only binfmt-elf-fdpic, not binfmt-flat. The only architectures I see that enable binfmt-flat are sh, xtensa and h8300, but only arch/sh uses CONFIG_BINFMT_SHARED_FLAT for a few machine specific configurations, and I'm in turn fairly sure those machines have not run a recent kernel in many years. The one SH nommu platform likely to have users is j2, and that is probably always used with musl-libc with elf-fdpic (given that Rich Felker maintains both the kernel port and the library). Arnd