From: Ben Hutchings <bhutchings@solarflare•com>
To: Greg Rose <gregory.v.rose@intel•com>
Cc: <netdev@vger•kernel.org>, <davem@davemloft•net>
Subject: Re: [RFC V2 PATCH] rtnetlink: Fix problem with buffer allocation
Date: Tue, 14 Feb 2012 21:13:13 +0000 [thread overview]
Message-ID: <1329253993.2443.30.camel@bwh-desktop> (raw)
In-Reply-To: <20120212191342.1458.70498.stgit@gitlad.jf.intel.com>
Thanks for persisting, Greg.
On Sun, 2012-02-12 at 11:13 -0800, Greg Rose wrote:
> Implement a new nlattr type IFLA_EXT_MASK. The mask is a 32 bit
> value that can be used to indicate to the kernel that certain
> extended ifinfo values are requested by the user application.
> At this time the only mask value created is RTEXT_FILTER_VF to
> indicate that the user wants the ifinfo dump to send information
> about the VFs belonging to the interface.
>
> I have kept the NLM_F_EXT nlmsg_flags bit to indicate to the kernel
> that the extended ifinfo dump filter mask is present. It does not
> act as the filter itself which has changed since the first submission
> of this RFC. Older versions of user applications won't set this
> flag which should fix the problem of some applications not allocating
> a large enough buffer for all the extended interface information.
[...]
> --- a/include/linux/netlink.h
> +++ b/include/linux/netlink.h
> @@ -59,6 +59,7 @@ struct nlmsghdr {
> #define NLM_F_MATCH 0x200 /* return all matching */
> #define NLM_F_ATOMIC 0x400 /* atomic GET */
> #define NLM_F_DUMP (NLM_F_ROOT|NLM_F_MATCH)
> +#define NLM_F_EXT 0x800 /* Get extended interface info such as VFs */
>
> /* Modifiers to NEW request */
> #define NLM_F_REPLACE 0x100 /* Override existing */
> @@ -215,6 +216,7 @@ int netlink_sendskb(struct sock *sk, struct sk_buff *skb);
> #else
> #define NLMSG_GOODSIZE SKB_WITH_OVERHEAD(8192UL)
> #endif
> +#define NLMSG_EXT_GOODSIZE SKB_WITH_OVERHEAD(32768UL)
This will probably do for now, but it would be preferable to really
calculate the maximum size.
I fear this is going to be too small in some cases while resulting in
allocation failures in others (that's an order-4 page allocation!).
Maybe reduce the message size slightly so that the skb data allocation
is within 32K?
[...]
> --- a/net/core/rtnetlink.c
> +++ b/net/core/rtnetlink.c
[...]
> @@ -1055,6 +1059,17 @@ static int rtnl_dump_ifinfo(struct sk_buff *skb, struct netlink_callback *cb)
> rcu_read_lock();
> cb->seq = net->dev_base_seq;
>
> + if (cb->nlh->nlmsg_flags && NLM_F_EXT) {
& not &&
> + struct rtattr *ext_req;
> + u32 *ext_req_data;
> + req = (struct rtnl_req_extended *)cb->nlh;
> + ext_req = (struct rtattr *)&req->ext;
> + if (ext_req->rta_type == IFLA_EXT_MASK) {
> + ext_req_data = RTA_DATA(ext_req);
> + ext_filter_mask = *ext_req_data;
> + }
> + }
We cannot trust a flag to tell us what the length of the message is. We
have to check the value of nlmsg_len (which netlink has already
validated as being within the skb length and >= our declared request
header length). I think that makes the flag redundant.
In fact, I think we should really use nlmsg_parse() here. That might be
overkill when there's only a single valid attribute; I don't know.
[...]
> @@ -1861,12 +1876,12 @@ static int rtnl_getlink(struct sk_buff *skb, struct nlmsghdr* nlh, void *arg)
> if (dev == NULL)
> return -ENODEV;
>
> - nskb = nlmsg_new(if_nlmsg_size(dev), GFP_KERNEL);
> + nskb = nlmsg_new(if_nlmsg_size(dev, 0), GFP_KERNEL);
> if (nskb == NULL)
> return -ENOBUFS;
>
> err = rtnl_fill_ifinfo(nskb, dev, RTM_NEWLINK, NETLINK_CB(skb).pid,
> - nlh->nlmsg_seq, 0, 0);
> + nlh->nlmsg_seq, 0, 0, 0);
> if (err < 0) {
> /* -EMSGSIZE implies BUG in if_nlmsg_size */
> WARN_ON(err == -EMSGSIZE);
It seems like this ought to support IFLA_EXT_MASK as well, though it's
maybe less important ('ip link' doesn't need it).
> @@ -1877,9 +1892,26 @@ static int rtnl_getlink(struct sk_buff *skb, struct nlmsghdr* nlh, void *arg)
> return err;
> }
>
> -static u16 rtnl_calcit(struct sk_buff *skb)
> +static u16 rtnl_calcit(struct sk_buff *skb, struct nlmsghdr *nlh)
> {
> - return min_ifinfo_dump_size;
> + struct rtnl_req_extended *req;
> + u32 ext_filter_mask = 0;
> +
> + if (nlh->nlmsg_flags && NLM_F_EXT) {
> + struct rtattr *ext_req;
> + u32 *ext_req_data;
> + req = (struct rtnl_req_extended *)&nlh;
> + ext_req = (struct rtattr *)&req->ext;
> + if (ext_req->rta_type == IFLA_EXT_MASK) {
> + ext_req_data = RTA_DATA(ext_req);
> + ext_filter_mask = *ext_req_data;
> + }
> + }
[...]
This has the same parsing problem as rtnl_dump_ifinfo().
Ben.
--
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.
next prev parent reply other threads:[~2012-02-14 21:13 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-02-12 19:13 [RFC V2 PATCH] rtnetlink: Fix problem with buffer allocation Greg Rose
2012-02-13 17:28 ` Stephen Hemminger
2012-02-13 18:24 ` Rose, Gregory V
2012-02-14 21:13 ` Ben Hutchings [this message]
2012-02-14 21:27 ` Rose, Gregory V
2012-02-14 21:31 ` David Miller
2012-02-14 21:41 ` Rose, Gregory V
2012-02-14 21:48 ` David Miller
2012-02-14 21:51 ` Rose, Gregory V
2012-02-15 14:08 ` Thomas Graf
2012-02-15 16:32 ` Rose, Gregory V
2012-02-14 21:22 ` David Miller
2012-02-14 21:34 ` Rose, Gregory V
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