linux-kernel - Re: [RFC PATCH for 4.18 1/2] rseq: use __u64 for rseq_cs fields, validate abort_ip < TASK

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CA+55aFzH+4=Aeh_P1ptFn5nVm7yFuEGpxUJ0kNB-sUHVOv8rcw@mail.gmail.com>
Date:   Mon, 2 Jul 2018 13:52:36 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Paul McKenney <paulmck@...ux.vnet.ibm.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Andy Lutomirski <luto@...capital.net>,
        Dave Watson <davejwatson@...com>, Paul Turner <pjt@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Russell King - ARM Linux <linux@....linux.org.uk>,
        Ingo Molnar <mingo@...hat.com>, Peter Anvin <hpa@...or.com>,
        Andi Kleen <andi@...stfloor.org>,
        Christoph Lameter <cl@...ux.com>, Ben Maurer <bmaurer@...com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Josh Triplett <josh@...htriplett.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Joel Fernandes <joelaf@...gle.com>
Subject: Re: [RFC PATCH for 4.18 1/2] rseq: use __u64 for rseq_cs fields,
 validate abort_ip < TASK_SIZE

On Mon, Jul 2, 2018 at 1:41 PM Mathieu Desnoyers
<mathieu.desnoyers@...icios.com> wrote:
>
> -       if (copy_from_user(rseq_cs, urseq_cs, sizeof(*rseq_cs)))
> +       if (copy_from_user(rseq_cs, urseq_cs, sizeof(*rseq_cs)) ||
> +           rseq_cs->abort_ip >= TASK_SIZE)
>                 return -EFAULT;

I think the abort_ip check should have the same error value as the
other sanity checks, ie just be of this format:

>         if (rseq_cs->version > 0)
>                 return -EINVAL;

also, I think you should check start_ip to be consistent. You kind of
accidentally do it with the check for

        if (rseq_cs->abort_ip - rseq_cs->start_ip - rseq_cs->post_commit_offset)

but honestly, that has underflow issues already, so I think you want
to basically make the check be

        if (rseq_cs->abort_ip >= TASK_SIZE)
                return -EINVAL;

        if (rseq_cs->start_ip >= rseq_cs->abort_ip)
                return -EINVAL;

which takes care of checkint  start_ip, and also the underflow for the
post_commit_offset check.

If somebody is depending on negative offsets, then that
post_commit_offset logic is already wrong.

> +       usig = (u32 __user *)(unsigned long)(rseq_cs->abort_ip - sizeof(u32));
>         ret = get_user(sig, usig);

That can underflow too, but I guess we can just rely on get_user()
getting it right.

               Linus