Patch "genetlink: fix counting regression on ctrl_dumpfamily()" has been added to the 4.10-stable tree

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

genetlink: fix counting regression on ctrl_dumpfamily()

to the 4.10-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:
genetlink-fix-counting-regression-on-ctrl_dumpfamily.patch
and it can be found in the queue-4.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Stanislaw Gruszka <[email protected]>
Date: Wed, 22 Mar 2017 16:08:33 +0100
Subject: genetlink: fix counting regression on ctrl_dumpfamily()

From: Stanislaw Gruszka <[email protected]>

[ Upstream commit 1d2a6a5e4bf2921531071fcff8538623dce74efa ]

Commit 2ae0f17df1cd ("genetlink: use idr to track families") replaced

	if (++n < fams_to_skip)
		continue;

into:

	if (n++ < fams_to_skip)
		continue;

This subtle change cause that on retry ctrl_dumpfamily() call we omit one family that failed to do ctrl_fill_info() on previous call, because cb->args[0] = n number counts also family that failed to do ctrl_fill_info().

Patch fixes the problem and avoid confusion in the future just decrease n counter when ctrl_fill_info() fail.

User visible problem caused by this bug is failure to get access to some genetlink family i.e. nl80211. However problem is reproducible only if number of registered genetlink families is big enough to cause second call of ctrl_dumpfamily().

---
 net/netlink/genetlink.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

@@ -783,8 +783,10 @@ static int ctrl_dumpfamily(struct sk_buf
 
 		if (ctrl_fill_info(rt, NETLINK_CB(cb->skb).portid,
 				   cb->nlh->nlmsg_seq, NLM_F_MULTI,
-				   skb, CTRL_CMD_NEWFAMILY) < 0)
+				   skb, CTRL_CMD_NEWFAMILY) < 0) {
+			n--;
 			break;
+		}
 	}
 
 	cb->args[0] = n;

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

queue-4.10/genetlink-fix-counting-regression-on-ctrl_dumpfamily.patch