Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <87h7wujhmz.fsf@x220.int.ebiederm.org> <87sgga6ze4.fsf@x220.int.ebiederm.org>
 <87v9l4zyla.fsf_-_@x220.int.ebiederm.org> <87eerszyim.fsf_-_@x220.int.ebiederm.org>
 <ee83587b-8a1c-3c4f-cc0f-7bc98afabae1@I-love.SAKURA.ne.jp>
In-Reply-To: <ee83587b-8a1c-3c4f-cc0f-7bc98afabae1@I-love.SAKURA.ne.jp>
From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Sun, 10 May 2020 12:38:20 -0700
Message-ID: <CAHk-=wgQ2ovXMW=5ZHCpowkE1PwPQSL7oV4YXzBxd6eqNRXxnQ@mail.gmail.com>
Subject: Re: [PATCH 3/5] exec: Remove recursion from search_binary_handler
To:     Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc:     "Eric W. Biederman" <ebiederm@xmission.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Oleg Nesterov <oleg@redhat.com>, Jann Horn <jannh@google.com>,
        Kees Cook <keescook@chromium.org>,
        Greg Ungerer <gerg@linux-m68k.org>,
        Rob Landley <rob@landley.net>,
        Bernd Edlinger <bernd.edlinger@hotmail.de>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Casey Schaufler <casey@schaufler-ca.com>,
        LSM List <linux-security-module@vger.kernel.org>,
        James Morris <jmorris@namei.org>,
        "Serge E. Hallyn" <serge@hallyn.com>,
        Andy Lutomirski <luto@amacapital.net>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Sat, May 9, 2020 at 9:30 PM Tetsuo Handa
<penguin-kernel@i-love.sakura.ne.jp> wrote:
>
> Wouldn't this change cause
>
>         if (fd_binary > 0)
>                 ksys_close(fd_binary);
>         bprm->interp_flags = 0;
>         bprm->interp_data = 0;
>
> not to be called when "Search for the interpreter" failed?

Good catch. We seem to have some subtle magic wrt the fd_binary file
descriptor, which depends on the recursive behavior.

I'm not seeing how to fix it cleanly with the "turn it into a loop".
Basically, that binfmt_misc use-case isn't really a tail-call.

Eric, ideas?

                 Linus