Re: KASAN: use-after-scope in ext4_group_desc_csum

[Jan Glauber]

On Fri, Oct 05, 2018 at 05:32:07PM +0200, Dmitry Vyukov wrote:
[...]

> This all makes me think that somebody else has left these 0xf8 in
> shadow before ext4_map_blocks started executing.
> Unfortunately debugging garbage in stack shadow is not completely
> trivial and there is no common recipe. I don't have setup to run arm64
> kernel at the moment. I would try to locate that garbage in stack
> shadow earlier, e.g. calling another function before ext4_map_blocks,
> implementing that function in mm/kasan/kasan.c (non-instrumented
> itself) and then try to scan stack and verify presence of 0xf8
> garbage. If this works out, then try to catch garbage earlier and/or
> try to figure out what function left that garbage (that's possible by
> locating 0x41b58ab3 magic:
> https://bugzilla.kernel.org/show_bug.cgi?id=198435).

Thanks a lot for your analysis! I'll try to debug this further but as
you pointed out it might be difficult to catch who writes beforehand to
that location.

--Jan