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From:   Paul Moore <paul@paul-moore.com>
Date:   Wed, 31 Jan 2018 04:06:37 -0500
Message-ID: <CAHC9VhTitwf5NLthRMxLdb=QrS+i7fDgVXq3qXkNmAt8ck8V3A@mail.gmail.com>
Subject: Re: [PATCH] general protection fault in sock_has_perm
To:     Greg KH <gregkh@linuxfoundation.org>
Cc:     Mark Salyzyn <salyzyn@android.com>,
        Stephen Smalley <sds@tycho.nsa.gov>,
        linux-kernel@vger.kernel.org, Eric Paris <eparis@parisplace.org>,
        James Morris <james.l.morris@oracle.com>,
        "Serge E. Hallyn" <serge@hallyn.com>, selinux@tycho.nsa.gov,
        linux-security-module@vger.kernel.org, stable@vger.kernel.org
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On Tue, Jan 30, 2018 at 5:46 PM, Greg KH <gregkh@linuxfoundation.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@paul-moore.com>

-- 
paul moore
www.paul-moore.com