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

David Gibson
2014-04-23T11:42:36Z

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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?

--
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

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