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

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Date:   Sun, 16 Sep 2018 19:38:55 +0200
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Jeff Layton <jlayton@...nel.org>
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: [RFC][PATCH 0/3] exec: Moving unshare_files_struct

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