linux-kernel - Re: [kernel-hardening] [RFC V2 4/6] lib: vsprintf: default kptr

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Message-ID: <CA+55aFwqyAzMR6PRYxu90Q2sB_cJ5JcP3ELH-BUGi-m0ti=X1w@mail.gmail.com>
Date:   Wed, 4 Oct 2017 12:23:02 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Jann Horn <jannh@...gle.com>
Cc:     Kees Cook <keescook@...omium.org>,
        "Tobin C. Harding" <me@...in.cc>,
        Greg KH <gregkh@...uxfoundation.org>,
        Petr Mladek <pmladek@...e.com>, Joe Perches <joe@...ches.com>,
        Ian Campbell <ijc@...lion.org.uk>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        William Roberts <william.c.roberts@...el.com>,
        Chris Fries <cfries@...gle.com>,
        Dave Weinstein <olorin@...gle.com>
Subject: Re: [kernel-hardening] [RFC V2 4/6] lib: vsprintf: default
 kptr_restrict to the maximum value

On Wed, Oct 4, 2017 at 12:13 PM, Jann Horn <jannh@...gle.com> wrote:
>
> Actually, /proc/kallsyms uses %pK, which hacks around this issue
> by checking for `euid != uid` in addition to the capability check - so this
> isn't exploitable through a typical setuid program.

Fair enough, you'd have to be a pretty broken suid program to have set
uid to euid before reading some untrusted file descriptor.

I could still imagine happening (hey, the X server used to sendmsg
file descriptors back and forth), but hopefully it's not really
realistic.

                  Linus