Commit 973462bb authored Apr 24, 2014 by David Gibson Committed by David S. Miller Apr 24, 2014

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



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@gibson.dropbear.id.au>
Reviewed-by: Jiri Pirko <jpirko@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent a64d90fd

net/core/rtnetlink.c

+12 −5

Original line number	Diff line number	Diff line
		@@ -1198,6 +1198,7 @@ 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];
		@@ -1218,11 +1219,17 @@ 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,
		err = rtnl_fill_ifinfo(skb, dev, RTM_NEWLINK,
		NETLINK_CB(cb->skb).portid,
		cb->nlh->nlmsg_seq, 0,
		NLM_F_MULTI,
		ext_filter_mask) <= 0)
		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));

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