On Mon, 27 May 2019, 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.
Last time I played with this, I couldn't figure out the toolchain to
produce shared libs. Only static executables worked fine. If I recall,
existing binfmt_flat distros don't use shared libs either.
For shared lib support on no-MMU target, binfmt_elf_fdpic is a much
saner choice.
Nicolas
