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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Wed, 3 Jun 2020 17:13:36 -0700
Message-ID: <CAHk-=wgTpLOeMjpLOc8hY7KC6Qv+jR-hBacyBSajJ6iUKasmKA@mail.gmail.com>
Subject: Re: [PATCH v5 0/3] close_range()
To:     Christian Brauner <christian.brauner@ubuntu.com>
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Kyle Evans <self@kyle-evans.net>,
        Victor Stinner <victor.stinner@gmail.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Linux API <linux-api@vger.kernel.org>,
        Florian Weimer <fweimer@redhat.com>,
        Jann Horn <jannh@google.com>, Oleg Nesterov <oleg@redhat.com>,
        Arnd Bergmann <arnd@arndb.de>, Shuah Khan <shuah@kernel.org>,
        David Howells <dhowells@redhat.com>,
        "Dmitry V. Levin" <ldv@altlinux.org>
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On Wed, Jun 3, 2020 at 4:24 PM Christian Brauner
<christian.brauner@ubuntu.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