linux-kernel - Re: [PATCH v6 5/6] binfmt_*: scope path resolution of interpreters

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Message-ID: <CAHk-=wh3dT7=SMjvSZreXSu36Cg7gsfSipLhfTz5ioDKXV5uHg@mail.gmail.com>
Date:   Sun, 12 May 2019 06:44:06 -0400
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Andrew Lutomirski <luto@...nel.org>, Jann Horn <jannh@...gle.com>,
        Aleksa Sarai <cyphar@...har.com>,
        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>,
        Eric Biederman <ebiederm@...ssion.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Christian Brauner <christian@...uner.io>,
        Tycho Andersen <tycho@...ho.ws>,
        David Drysdale <drysdale@...gle.com>,
        Chanho Min <chanho.min@....com>,
        Oleg Nesterov <oleg@...hat.com>, Aleksa Sarai <asarai@...e.de>,
        Linux Containers <containers@...ts.linux-foundation.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        kernel list <linux-kernel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>
Subject: Re: [PATCH v6 5/6] binfmt_*: scope path resolution of interpreters

On Sat, May 11, 2019 at 7:37 PM Andy Lutomirski <luto@...capital.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