linux-kernel - Re: [PATCH v5 0/3] close

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Message-ID: <CAHk-=wgTpLOeMjpLOc8hY7KC6Qv+jR-hBacyBSajJ6iUKasmKA@mail.gmail.com>
Date:   Wed, 3 Jun 2020 17:13:36 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Christian Brauner <christian.brauner@...ntu.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Kyle Evans <self@...e-evans.net>,
        Victor Stinner <victor.stinner@...il.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        Florian Weimer <fweimer@...hat.com>,
        Jann Horn <jannh@...gle.com>, Oleg Nesterov <oleg@...hat.com>,
        Arnd Bergmann <arnd@...db.de>, Shuah Khan <shuah@...nel.org>,
        David Howells <dhowells@...hat.com>,
        "Dmitry V. Levin" <ldv@...linux.org>
Subject: Re: [PATCH v5 0/3] close_range()

On Wed, Jun 3, 2020 at 4:24 PM Christian Brauner
<christian.brauner@...ntu.com> wrote:
>
> Ok, here's what I have. Does the below look somewhat sane?

Probably. Needs lots of testing. But this one looks wrong:

> +int __close_range(unsigned fd, unsigned max_fd, unsigned int flags)
>  {
> +               if ((max_fd + 1) >= cur_max)
> +                       max_unshare_fds = fd;

A normal value for "close everything starting at X" would have a
max_fd value of ~0.

So "max_fd+1" would overflow to 0, and then this would never trigger.

Other than that it looks what what I imagine my feverdreams were about.

              Linus