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

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Message-ID: <99c11fa6-ad9a-830c-467e-6a56e78aecf8@android.com>
Date:   Tue, 30 Jan 2018 11:00:04 -0800
From:   Mark Salyzyn <salyzyn@...roid.com>
To:     Stephen Smalley <sds@...ho.nsa.gov>, linux-kernel@...r.kernel.org
Cc:     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 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;