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

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Date:   Tue, 30 Jan 2018 23:46:14 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Mark Salyzyn <salyzyn@...roid.com>
Cc:     Stephen Smalley <sds@...ho.nsa.gov>, linux-kernel@...r.kernel.org,
        Paul Moore <paul@...l-moore.com>,
        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 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.

thanks,

greg k-h