Hello Arnd, all, On Wed, 2019-05-29 at 14:05 +0200, Arnd Bergmann wrote:
On Tue, May 28, 2019 at 12:56 PM Greg Ungerer <gerg@xxxxxxxxxxxxxx> wrote:On 27/5/19 11:38 pm, Jann Horn wrote:On Sat, May 25, 2019 at 11:43 PM Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:On Fri, 24 May 2019 22:18:17 +0200 Jann Horn <jannh@xxxxxxxxxx> 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@xxxxxxxxxxxxxxx Fixes: 287980e49ffc ("remove lots of IS_ERR_VALUE abuses") Signed-off-by: Jann Horn <jannh@xxxxxxxxxx> --- 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.
We use both, acutally, but all-static. We don't support shared libraries with bFLT or ELF FDPIC. Kind regards, Sergei
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
