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

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Message-ID: <CAHk-=wiExfaVhUTvKj7hR6DG4C2+oy6usz0Sa6QbPr5EgDH28w@mail.gmail.com>
Date:   Wed, 4 Sep 2019 14:36:48 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Aleksa Sarai <cyphar@...har.com>
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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        Namhyung Kim <namhyung@...nel.org>,
        Aleksa Sarai <asarai@...e.de>,
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Subject: Re: [PATCH v12 10/12] namei: aggressively check for nd->root escape
 on ".." resolution

On Wed, Sep 4, 2019 at 2:35 PM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> On Wed, Sep 4, 2019 at 2:09 PM Linus Torvalds
> <torvalds@...ux-foundation.org> wrote:
> >
> > So you'd have three stages:
> >
> >  1) ".." always returns -EXDEV
> >
> >  2) ".." returns -EXDEV if there was a concurrent rename/mount
> >
> >  3) ".." returns -EXDEV if there was a concurrent rename/mount and we
> > reset the sequence numbers and check if you escaped.
>
> In fact, I wonder if this should return -EAGAIN instead - to say that
> "retrying may work".

And here "this" was meant to be "case 2" - I was moving the quoted
text around and didn't fix my wording, so now it is ambiguous or
implies #3, which would be crazy.

Sorry for the confusion,

            Linus