linux-kernel - Re: [RFC][PATCH 0/3] exec: Moving unshare_files

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Message-ID: <c7e4a674b86760e7878aa8dc66988f38db235ec3.camel@kernel.org>
Date:   Mon, 17 Sep 2018 12:24:57 -0400
From:   Jeff Layton <jlayton@...nel.org>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     viro@...iv.linux.org.uk, berrange@...hat.com,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Oleg Nesterov <oleg@...hat.com>
Subject: Re: [RFC][PATCH 0/3] exec: Moving unshare_files_struct

On Sun, 2018-09-16 at 19:38 +0200, Eric W. Biederman wrote:
> Paired with Oleg's patch to reduce the number of callers of
> get_files_struct it looks like we can simplify the basic idea of moving
> unshare_files in exec by quite a bit so that in net we have fewer lines
> of code.
> 
> The big simplification from Jeff's verion is that we take advantage
> of calling unshare_files past the point of no return.  Which removes
> the need for cleanup, and restoring ->files.  Which removes the
> need for blocking clone and unshare.
> 
> Oleg's patch to remove get_files_struct from proc means we don't need
> two counts in files_struct.
> 
> Which leaves us with the question of what are the races in fs/exec.c
> with respect to accessing files.  Semantically I don't think we care
> but we do need to be certain the implementation of exec is still robust.
> 
> These patches are still rough and ready and only compile tested but I
> believe they demonstrate what is possible.
> 
> Eric W. Biederman (3):
>       exec: Move unshare_files down to avoid locks being dropped on exec.
>       exec: Simplify unshare_files
>       exec: Remove reset_files_struct
> 
>  fs/coredump.c           |  5 +----
>  fs/exec.c               | 16 +++++-----------
>  fs/file.c               | 12 ------------
>  include/linux/fdtable.h |  3 +--
>  kernel/fork.c           | 12 ++++++------
>  5 files changed, 13 insertions(+), 35 deletions(-)
> 
> Eric

Much better than what I had proposed and I do like that diffstat. You
can add this from me too:

    Reviewed-by: Jeff Layton <jlayton@...nel.org>

Maybe get this into -next soon once it has passed some sanity tests?

Thanks,
-- 
Jeff Layton <jlayton@...nel.org>