[3.11.y.z extended stable] Patch "rtnetlink: Warn when interface's information won't fit in our packet" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    rtnetlink: Warn when interface's information won't fit in our packet

to the linux-3.11.y-queue branch of the 3.11.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.11.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.11.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From b3c0b5d373010a7f92b6d6442b2e38cb9e8e8e30 Mon Sep 17 00:00:00 2001
From: David Gibson <david at gibson.dropbear.id.au>
Date: Thu, 24 Apr 2014 10:22:35 +1000
Subject: rtnetlink: Warn when interface's information won't fit in our packet

commit 973462bbde79bb827824c73b59027a0aed5c9ca6 upstream.

Without IFLA_EXT_MASK specified, the information reported for a single
interface in response to RTM_GETLINK is expected to fit within a netlink
packet of NLMSG_GOODSIZE.

If it doesn't, however, things will go badly wrong,  When listing all
interfaces, netlink_dump() will incorrectly treat -EMSGSIZE on the first
message in a packet as the end of the listing and omit information for
that interface and all subsequent ones.  This can cause getifaddrs(3) to
enter an infinite loop.

This patch won't fix the problem, but it will WARN_ON() making it easier to
track down what's going wrong.

Signed-off-by: David Gibson <david at gibson.dropbear.id.au>
Reviewed-by: Jiri Pirko <jpirko at redhat.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 net/core/rtnetlink.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index 6f73a1094abb..415e33ecd503 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -1048,6 +1048,7 @@ static int rtnl_dump_ifinfo(struct sk_buff *skb, struct netlink_callback *cb)
 	struct hlist_head *head;
 	struct nlattr *tb[IFLA_MAX+1];
 	u32 ext_filter_mask = 0;
+	int err;

 	s_h = cb->args[0];
 	s_idx = cb->args[1];
@@ -1068,11 +1069,17 @@ static int rtnl_dump_ifinfo(struct sk_buff *skb, struct netlink_callback *cb)
 		hlist_for_each_entry_rcu(dev, head, index_hlist) {
 			if (idx < s_idx)
 				goto cont;
-			if (rtnl_fill_ifinfo(skb, dev, RTM_NEWLINK,
-					     NETLINK_CB(cb->skb).portid,
-					     cb->nlh->nlmsg_seq, 0,
-					     NLM_F_MULTI,
-					     ext_filter_mask) <= 0)
+			err = rtnl_fill_ifinfo(skb, dev, RTM_NEWLINK,
+					       NETLINK_CB(cb->skb).portid,
+					       cb->nlh->nlmsg_seq, 0,
+					       NLM_F_MULTI,
+					       ext_filter_mask);
+			/* If we ran out of room on the first message,
+			 * we're in trouble
+			 */
+			WARN_ON((err == -EMSGSIZE) && (skb->len == 0));
+
+			if (err <= 0)
 				goto out;

 			nl_dump_check_consistent(cb, nlmsg_hdr(skb));
--
1.9.1