[PATCH] rtnetlink: Fix message size calculation for link messages

[PATCH] rtnetlink: Fix message size calculation for link messages

[Thomas Graf]

nlmsg_total_size() calculates the length of a netlink message
including header and alignment. nla_total_size() calculates the
space an individual attribute consumes which was meant to be used
in this context.

Also, ensure to account for the attribute header for the
IFLA_INFO_XSTATS attribute as implementations of get_xstats_size()
seem to assume that we do so.

The addition of two message headers minus the missing attribute
header resulted in a calculated message size that was larger than
required. Therefore we never risked running out of skb tailroom.

Signed-off-by: Thomas Graf <tgraf@infradead.org>
Cc: Patrick McHardy <kaber@trash.net>

Index: net-2.6/net/core/rtnetlink.c
===================================================================
--- net-2.6.orig/net/core/rtnetlink.c
+++ net-2.6/net/core/rtnetlink.c
@@ -347,16 +347,17 @@ static size_t rtnl_link_get_size(const s
 	if (!ops)
 		return 0;
 
-	size = nlmsg_total_size(sizeof(struct nlattr)) + /* IFLA_LINKINFO */
-	       nlmsg_total_size(strlen(ops->kind) + 1);	 /* IFLA_INFO_KIND */
+	size = nla_total_size(sizeof(struct nlattr)) + /* IFLA_LINKINFO */
+	       nla_total_size(strlen(ops->kind) + 1);  /* IFLA_INFO_KIND */
 
 	if (ops->get_size)
 		/* IFLA_INFO_DATA + nested data */
-		size += nlmsg_total_size(sizeof(struct nlattr)) +
+		size += nla_total_size(sizeof(struct nlattr)) +
 			ops->get_size(dev);
 
 	if (ops->get_xstats_size)
-		size += ops->get_xstats_size(dev);	/* IFLA_INFO_XSTATS */
+		/* IFLA_INFO_XSTATS */
+		size += nla_total_size(ops->get_xstats_size(dev));
 
 	return size;
 }

Re: [PATCH] rtnetlink: Fix message size calculation for link messages

[Patrick McHardy]

On 12.11.2010 02:47, Thomas Graf wrote:
> nlmsg_total_size() calculates the length of a netlink message
> including header and alignment. nla_total_size() calculates the
> space an individual attribute consumes which was meant to be used
> in this context.
> 
> Also, ensure to account for the attribute header for the
> IFLA_INFO_XSTATS attribute as implementations of get_xstats_size()
> seem to assume that we do so.
> 
> The addition of two message headers minus the missing attribute
> header resulted in a calculated message size that was larger than
> required. Therefore we never risked running out of skb tailroom.
> 
> Signed-off-by: Thomas Graf <tgraf@infradead.org>
> Cc: Patrick McHardy <kaber@trash.net>

Looks good to me, thanks Thomas.

Acked-by: Patrick McHardy <kaber@trash.net>

Re: [PATCH] rtnetlink: Fix message size calculation for link messages

[David Miller]

From: Patrick McHardy <kaber@trash.net>
Date: Fri, 12 Nov 2010 08:43:46 +0100

> On 12.11.2010 02:47, Thomas Graf wrote:
>> nlmsg_total_size() calculates the length of a netlink message
>> including header and alignment. nla_total_size() calculates the
>> space an individual attribute consumes which was meant to be used
>> in this context.
>> 
>> Also, ensure to account for the attribute header for the
>> IFLA_INFO_XSTATS attribute as implementations of get_xstats_size()
>> seem to assume that we do so.
>> 
>> The addition of two message headers minus the missing attribute
>> header resulted in a calculated message size that was larger than
>> required. Therefore we never risked running out of skb tailroom.
>> 
>> Signed-off-by: Thomas Graf <tgraf@infradead.org>
>> Cc: Patrick McHardy <kaber@trash.net>
> 
> Looks good to me, thanks Thomas.
> 
> Acked-by: Patrick McHardy <kaber@trash.net>

Applied, thanks.