Re: [PATCH] proc: Fix uninitialized byte read in get_mm_cmdline()

[Jakub Jankowski]

On 2019-07-12, Alexey Izbyshev wrote:

> On 7/12/19 8:46 PM, Alexey Dobriyan wrote:
> > The proper fix to all /proc/*/cmdline problems is to revert
> >
> > 	f5b65348fd77839b50e79bc0a5e536832ea52d8d
> > 	proc: fix missing final NUL in get_mm_cmdline() rewrite
> >
> > 	5ab8271899658042fabc5ae7e6a99066a210bc0e
> > 	fs/proc: simplify and clarify get_mm_cmdline() function
> Should this be interpreted as an actual suggestion to revert the patches,
> fix the conflicts, test and submit them, or is this more like thinking out
> loud? In the former case, will it be OK for long term branches?
>
> get_mm_cmdline() does seem easier to read for me before 5ab8271899658042.
> But it also has different semantics in corner cases, for example:
>
> - If there is no NUL at arg_end-1, it reads only the first string in
> the combined arg/env block, and doesn't terminate it with NUL.
>
> - If there is any problem with access_remote_vm() or copy_to_user(),
> it returns -EFAULT even if some data were copied to userspace.
>
> On the other hand, 5ab8271899658042 was merged not too long ago (about a year),
> so it's possible that the current semantics isn't heavily relied upon.

I posted this (corner?) case ~3 months ago, unfortunately it wasn't picked 
up by anyone: https://lkml.org/lkml/2019/4/5/825
You can treat it as another datapoint in this discussion.


Regards,
 Jakub

--
Jakub Jankowski|shasta@xxxxxxxxxxx|https://toxcorp.com/