linux-kernel - Re: [PATCH] general protection fault in sock_has

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Date:   Thu, 1 Feb 2018 09:18:11 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Paul Moore <paul@...l-moore.com>,
        Mark Salyzyn <salyzyn@...roid.com>
Cc:     Stephen Smalley <sds@...ho.nsa.gov>, linux-kernel@...r.kernel.org,
        Eric Paris <eparis@...isplace.org>,
        James Morris <james.l.morris@...cle.com>,
        "Serge E. Hallyn" <serge@...lyn.com>, selinux@...ho.nsa.gov,
        linux-security-module@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] general protection fault in sock_has_perm

On Wed, Jan 31, 2018 at 04:06:37AM -0500, Paul Moore wrote:
> On Tue, Jan 30, 2018 at 5:46 PM, Greg KH <gregkh@...uxfoundation.org> wrote:
> > On Tue, Jan 30, 2018 at 11:00:04AM -0800, Mark Salyzyn wrote:
> >> On 01/19/2018 09:41 AM, Stephen Smalley wrote:
> >> > If we can't safely dereference the sock in these hooks, then that seems
> >> > to point back to the approach used in my original code, where in
> >> > ancient history I had sock_has_perm() take the socket and use its inode
> >> > i_security field instead of the sock.  commit
> >> > 253bfae6e0ad97554799affa0266052968a45808 switched them to use the sock
> >> > instead.
> >>
> >> Because of the nature of this problem (hard to duplicate, no clear path), I
> >> am understandably not comfortable reverting and submitting for testing in
> >> order to prove this point. It is disruptive because it changes several
> >> subroutine call signatures.
> >>
> >> AFAIK this looks like a user request racing in without reference counting or
> >> RCU grace period in the callers (could be viewed as not an issue with
> >> security code). Effectively fixed in 4.9-stable, but broken in 4.4-stable.
> >>
> >> hygiene, KISS and small, is all I do feel comfortable to submit to
> >> 4.4-stable without pulling in all the infrastructure improvements.
> >>
> >> -- Mark
> >>
> >> ---
> >>  security/selinux/hooks.c | 2 ++
> >>  1 file changed, 2 insertions(+)
> >>
> >> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> >> index 34427384605d..be68992a28cb 100644
> >> --- a/security/selinux/hooks.c
> >> +++ b/security/selinux/hooks.c
> >> @@ -4066,6 +4066,8 @@ static int sock_has_perm(struct task_struct *task,
> >> struct sock *sk, u32 perms)
> >>      struct lsm_network_audit net = {0,};
> >>      u32 tsid = task_sid(task);
> >>
> >> +    if (!sksec)
> >> +        return -EFAULT;
> >>      if (sksec->sid == SECINITSID_KERNEL)
> >>          return 0;
> >>
> >
> > This looks sane to me as a simple 4.4-only fix.  If the SELinux
> > maintainer acks it, I can easily queue this up.
> 
> This revision addresses my concerns with Mark's previous patch.
> 
> Acked-by: Paul Moore <paul@...l-moore.com>

Wonderful!

Mark, can you resend this in a format I can apply it in?

thanks,

greg k-h