Re: [PATCH v2 02/24] exec: Simplify unshare_files

[Al Viro]

On Mon, Nov 23, 2020 at 10:25:13AM -0800, Linus Torvalds wrote:
> On Mon, Nov 23, 2020 at 9:52 AM Oleg Nesterov <oleg@xxxxxxxxxx> wrote:
> >
> > Can anyone explain why does do_coredump() need unshare_files() at all?
> 
> Hmm. It goes back to 2012, and it's placed just before calling
> "->core_dump()", so I assume some core dumping function messed with
> the file table back when..
> 
> I can't see anything like that currently.
> 
> The alternative is that core-dumping just keeps the file table around
> for a long while, and thus files don't actually close in a timely
> manner. So it might not be a "correctness" issue as much as a latency
> issue.

IIRC, it was "weird architecture hooks might be playing silly buggers
with some per-descriptor information they want in coredumps, better
make sure it can't change under them"; it doesn't cost much and
it reduced the analysis surface nicely.

Had been a while ago, so the memories might be faulty...  Anyway, that
reasoning seems to be applicable right now - rather than keeping an
eye on coredump logics on random architectures that might be looking
at descriptor table in unsafe way, just make sure they have a stable
private table and be done with that.

How much is simplified by not doing it there, anyway?