Looks ok to me too. But I suggest we let David apply the pending patch as is to net, as that code is still wrong, and then post this improvement to net-next later.

///jon

-----Original Message-----
From: Tommi Rantala [mailto:tommi.t.rantala@nokia.com]
Sent: Friday, December 01, 2017 09:03
To: Ying Xue <redacted>; Jon Maloy
[off-list ref]; David S. Miller [off-list ref];
netdev@vger.kernel.org; tipc-discussion@lists.sourceforge.net; linux-
kernel@vger.kernel.org
Subject: Re: [PATCH net v2] tipc: call tipc_rcv() only if bearer is up in
tipc_udp_recv()

On 01.12.2017 15:18, Ying Xue wrote:

quoted

On 11/30/2017 08:32 PM, Tommi Rantala wrote:

quoted

quoted

In my opinion, the real root cause of the issue is because we too
early set a not-yet-initialized bearer instance to ub->bearer
through rcu_assign_pointer(ub->bearer, b) in tipc_udp_enable().
Instead if we assign the bearer pointer at the end of
tipc_udp_enable() where the bearer has been completed the

initialization, the issue would be avoided.

quoted

quoted

Hi, sorry, I fail to see how that helps.

bearer->tolerance is only initialized in tipc_enable_bearer() after
calling m->enable_media() ie. tipc_udp_enable().

So even if we do "rcu_assign_pointer(ub->bearer, b)" later in
tipc_udp_enable(), bearer->tolerance will still be uninitialized, and
the crash can happen.

Sorry, I missed the point that b->tolerance is not uninitialized when
we assign bearer pointer to ub->bearer later.

But in my view the issue happened is because we enable media too early.
So it's better to change the code as belows:

Thanks, looks good to me!

Tested in 4.4 (which does not have b->up), and this fixes the oops also there.

-Tommi

quoted

diff --git a/net/tipc/bearer.c b/net/tipc/bearer.c index

47ec121..ec6f02a 100644

--- a/net/tipc/bearer.c
+++ b/net/tipc/bearer.c

@@ -320,19 +320,18 @@ static int tipc_enable_bearer(struct net *net,

const char *name,

         strcpy(b->name, name);
         b->media = m;
-       res = m->enable_media(net, b, attr);
-       if (res) {
-               pr_warn("Bearer <%s> rejected, enable failure (%d)\n",
-                       name, -res);
-               return -EINVAL;
-       }
-
         b->identity = bearer_id;
         b->tolerance = m->tolerance;
         b->window = m->window;
         b->domain = disc_domain;
         b->net_plane = bearer_id + 'A';
         b->priority = priority;
+       res = m->enable_media(net, b, attr);
+       if (res) {
+               pr_warn("Bearer <%s> rejected, enable failure (%d)\n",
+                       name, -res);
+               return -EINVAL;
+       }
         test_and_set_bit_lock(0, &b->up);