linux-kernel - Re: [BUG]: bad usercopy in kvm_stats

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Message-ID: <ZK2ABPwCke32Kh0q@google.com>
Date:   Tue, 11 Jul 2023 09:15:00 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Zheng Zhang <zheng.zhang@...il.ucr.edu>, keescook@...omium.org,
        linux-hardening@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [BUG]: bad usercopy in kvm_stats_read in mm/usercopy.c

On Mon, Jul 10, 2023, Andrew Morton wrote:
> On Sun, 9 Jul 2023 14:32:09 -0700 Zheng Zhang <zheng.zhang@...il.ucr.edu> wrote:
> 
> > Kees, Andrew, and  to whom it may concern:
> > 
> > Hello! We have found a bug in the Linux kernel version 6.2.0 by syzkaller
> > with our own templates. It also produces a POC.
> > Attached is the report, log, and reproducers generated by syzkaller
> > Please let me know if there is any additional information that I can
> > provide to help debug this issue.
> > Thanks!
> 
> Let's cc the kvm mailing list.
> 
> Original email is at
> https://lkml.kernel.org/r/CAC_GQSr3xzZaeZt85k_RCBd5kfiOve8qXo7a81Cq53LuVQ5r=Q@mail.gmail.com

Yeaaaah.  We failed kernel programming 101.  KVM installs file descriptors to
let userspace read VM and vCPU stats, but doesn't grab a reference to the VM to
ensure the VM and its vCPUs are kept alive until the stats fds are closed.  I'll
send a patch.