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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Sun, 12 May 2019 06:44:06 -0400
Message-ID: <CAHk-=wh3dT7=SMjvSZreXSu36Cg7gsfSipLhfTz5ioDKXV5uHg@mail.gmail.com>
Subject: Re: [PATCH v6 5/6] binfmt_*: scope path resolution of interpreters
To:     Andy Lutomirski <luto@amacapital.net>
Cc:     Andrew Lutomirski <luto@kernel.org>, Jann Horn <jannh@google.com>,
        Aleksa Sarai <cyphar@cyphar.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Jeff Layton <jlayton@kernel.org>,
        "J. Bruce Fields" <bfields@fieldses.org>,
        Arnd Bergmann <arnd@arndb.de>,
        David Howells <dhowells@redhat.com>,
        Eric Biederman <ebiederm@xmission.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Christian Brauner <christian@brauner.io>,
        Tycho Andersen <tycho@tycho.ws>,
        David Drysdale <drysdale@google.com>,
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On Sat, May 11, 2019 at 7:37 PM Andy Lutomirski <luto@amacapital.net> wrote:
>
> I bet this will break something that already exists. An execveat() flag to turn off /proc/self/exe would do the trick, though.

Thinking more about it, I suspect it is (once again) wrong to let the
thing that does the execve() control that bit.

Generally, the less we allow people to affect the lifetime and
environment of a suid executable, the better off we are.

But maybe we could limit /proc/*/exe to at least not honor suid'ness
of the target? Or does chrome/runc depend on that too?

             Linus