[Devel] [PATCH] proc: check vma->vm_file before dereferencing

[Cyrill Gorcunov]

On Mon, Oct 15, 2012 at 02:40:48PM -0700, Andrew Morton wrote:
> On Mon, 15 Oct 2012 19:30:03 +0400
> Stanislav Kinsbursky <skinsbursky at parallels.com> wrote:
> 
> > It can be equal to NULL.
> > 
> 
> Please write better changelogs, so people do not have to ask questions
> such as:
> 
> - Under what conditions does this bug trigger?
> 
> - In which kernel version(s)?
> 
> - Is it a post-3.6 regression?

Andrew, would the following changelog be enough?

The commit 7b540d0646ce122f0ba4520412be91e530719742 switched
proc_map_files_readdir to use @f_mode directly instead of grabbing
@file reference, but same time the test for @vm_file presence was
lost leading to nil dereference. The patch brings the test back.

The all proc_map_files feature is CONFIG_CHECKPOINT_RESTORE wrapped
(which is set to 'n' by default) so the bug doesn't affect regular
kernels.

The regression is 3.7-rc1 only as far as I can tell.