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

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

netlink: do not proceed 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-proceed-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 <[email protected]> know about it.

From: "Jason A. Donenfeld" <[email protected]>
Date: Thu, 28 Sep 2017 00:41:44 +0200
Subject: netlink: do not proceed if dump's start() errs

From: "Jason A. Donenfeld" <[email protected]>

[ Upstream commit fef0035c0f31322d417d1954bba5ab959bf91183 ]

Drivers that use the start method for netlink dumping rely on dumpit not being called if start fails. For example, ila_xlat.c allocates memory and assigns it to cb->args[0] in its start() function. It might fail to do that and return -ENOMEM instead. However, even when returning an error, dumpit will be called, which, in the example above, quickly dereferences the memory in cb->args[0], which will OOPS the kernel. This is but one example of how this goes wrong.

Since start() has always been a function with an int return type, it therefore makes sense to use it properly, rather than ignoring it. This patch thus returns early and does not call dumpit() when start() fails.

---
 net/netlink/af_netlink.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

@@ -2211,10 +2211,13 @@ int __netlink_dump_start(struct sock *ss
 
 	mutex_unlock(nlk->cb_mutex);
 
+	ret = 0;
 	if (cb->start)
-		cb->start(cb);
+		ret = cb->start(cb);
+
+	if (!ret)
+		ret = netlink_dump(sk);
 
-	ret = netlink_dump(sk);
 	sock_put(sk);
 
 	if (ret)

Patches currently in stable-queue which might be from [email protected] are

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