Patch "netlink: do not set cb_running if dump's start() errs" has been added to the 4.9-stable tree

Patch "netlink: do not set cb_running if dump's start() errs" has been added to the 4.9-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    netlink: do not set cb_running if dump's start() errs

to the 4.9-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     netlink-do-not-set-cb_running-if-dump-s-start-errs.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From foo@baz Wed Nov 15 17:24:03 CET 2017
From: "Jason A. Donenfeld" <Jason@zx2c4.com>
Date: Mon, 9 Oct 2017 14:14:51 +0200
Subject: netlink: do not set cb_running if dump's start() errs

From: "Jason A. Donenfeld" <Jason@zx2c4.com>


[ Upstream commit 41c87425a1ac9b633e0fcc78eb1f19640c8fb5a0 ]

It turns out that multiple places can call netlink_dump(), which means
it's still possible to dereference partially initialized values in
dump() that were the result of a faulty returned start().

This fixes the issue by calling start() _before_ setting cb_running to
true, so that there's no chance at all of hitting the dump() function
through any indirect paths.

It also moves the call to start() to be when the mutex is held. This has
the nice side effect of serializing invocations to start(), which is
likely desirable anyway. It also prevents any possible other races that
might come out of this logic.

In testing this with several different pieces of tricky code to trigger
these issues, this commit fixes all avenues that I'm aware of.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Cc: Johannes Berg <johannes@sipsolutions.net>
Reviewed-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/netlink/af_netlink.c |   13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -2207,16 +2207,17 @@ int __netlink_dump_start(struct sock *ss
 	cb->min_dump_alloc = control->min_dump_alloc;
 	cb->skb = skb;
 
+	if (cb->start) {
+		ret = cb->start(cb);
+		if (ret)
+			goto error_unlock;
+	}
+
 	nlk->cb_running = true;
 
 	mutex_unlock(nlk->cb_mutex);
 
-	ret = 0;
-	if (cb->start)
-		ret = cb->start(cb);
-
-	if (!ret)
-		ret = netlink_dump(sk);
+	ret = netlink_dump(sk);
 
 	sock_put(sk);
 


Patches currently in stable-queue which might be from Jason@zx2c4.com are

queue-4.9/netlink-do-not-set-cb_running-if-dump-s-start-errs.patch