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

Sergei Shtylyov
2014-04-23T14:20:17Z

Hello.

On 23-04-2014 11:21, David Gibson 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
[...]
> @@ -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 */

Hm, comment style... multi-line comments in the networking code should
look like this:

/* bla
* bla
*/

> + WARN_ON((err == -EMSGSIZE) && (skb->len == 0));
> +
> + if (err <= 0)

WBR, Sergei