linux-kernel - Re: [PATCH v12 10/12] namei: aggressively check for nd->root escape on ".." resolution

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Message-ID: <20592.1567636276@warthog.procyon.org.uk>
Date:   Wed, 04 Sep 2019 23:31:16 +0100
From:   David Howells <dhowells@...hat.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        Jeff Layton <jlayton@...nel.org>,
        "J. Bruce Fields" <bfields@...ldses.org>,
        Arnd Bergmann <arnd@...db.de>,
        David Howells <dhowells@...hat.com>,
        Shuah Khan <shuah@...nel.org>,
        Shuah Khan <skhan@...uxfoundation.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Christian Brauner <christian@...uner.io>,
        Jann Horn <jannh@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Eric Biederman <ebiederm@...ssion.com>,
        Andy Lutomirski <luto@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Tycho Andersen <tycho@...ho.ws>,
        David Drysdale <drysdale@...gle.com>,
        Chanho Min <chanho.min@....com>,
        Oleg Nesterov <oleg@...hat.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
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Subject: Re: [PATCH v12 10/12] namei: aggressively check for nd->root escape on ".." resolution

Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> > Hinting to userspace to do a retry (with -EAGAIN as you mention in your
> > other mail) wouldn't be a bad thing at all, though you'd almost
> > certainly get quite a few spurious -EAGAINs -- &{mount,rename}_lock are
> > global for the entire machine, after all.
> 
> I'd hope that we have some future (possibly very long-term)
> alternative that is not quite system-global, but yes, right now they
> are.

It ought to be reasonably easy to make them per-sb at least, I think.  We
don't allow cross-super rename, right?

David