Re: [PATCH 1/2] rtnetlink: Warn when interface's information won't fit in our packet

Jiri Pirko
2014-04-23T11:51:37Z

Wed, Apr 23, 2014 at 01:41:20PM CEST, david@gibson.dropbear.id.au wrote:
>On Wed, Apr 23, 2014 at 11:09:05AM +0200, Jiri Pirko wrote:
>> Wed, Apr 23, 2014 at 09:21:04AM CEST, david@gibson.dropbear.id.au wrote:
>> >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>
>> >---
>> > net/core/rtnetlink.c | 16 +++++++++++-----
>> > 1 file changed, 11 insertions(+), 5 deletions(-)
>> >
>> >diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
>> >index d4ff417..5331db2 100644
>> >--- a/net/core/rtnetlink.c
>> >+++ b/net/core/rtnetlink.c
>> >@@ -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 +1219,16 @@ 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)
>> if (err)
>
><= 0 was what the original version had. Why do you think it should be
>changed to != 0?

You are right. I misread rtnl_fill_ifinfo.

>
>--
>David Gibson | I'll have my music baroque, and my code
>david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
> | _way_ _around_!
>http://www.ozlabs.org/~dgibson