netdev - [PATCH net-next 06/17] netlink: Avoid netlink mmap alloc if msg size exceeds frame size

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Date:	Mon,  6 Jan 2014 16:16:05 -0800
From:	Jesse Gross <jesse@...ira.com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org, dev@...nvswitch.org,
	Thomas Graf <tgraf@...g.ch>,
	Daniel Borkmann <dborkman@...hat.com>,
	Jesse Gross <jesse@...ira.com>
Subject: [PATCH net-next 06/17] netlink: Avoid netlink mmap alloc if msg size exceeds frame size

From: Thomas Graf <tgraf@...g.ch>

An insufficent ring frame size configuration can lead to an
unnecessary skb allocation for every Netlink message. Check frame
size before taking the queue lock and allocating the skb and
re-check with lock to be safe.

Signed-off-by: Thomas Graf <tgraf@...g.ch>
Reviewed-by: Daniel Borkmann <dborkman@...hat.com>
Signed-off-by: Jesse Gross <jesse@...ira.com>
---
 net/netlink/af_netlink.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index bca50b9..6433489 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -1769,6 +1769,9 @@ struct sk_buff *netlink_alloc_skb(struct sock *ssk, unsigned int size,
 	if (ring->pg_vec == NULL)
 		goto out_put;
 
+	if (ring->frame_size - NL_MMAP_HDRLEN < size)
+		goto out_put;
+
 	skb = alloc_skb_head(gfp_mask);
 	if (skb == NULL)
 		goto err1;
@@ -1778,6 +1781,7 @@ struct sk_buff *netlink_alloc_skb(struct sock *ssk, unsigned int size,
 	if (ring->pg_vec == NULL)
 		goto out_free;
 
+	/* check again under lock */
 	maxlen = ring->frame_size - NL_MMAP_HDRLEN;
 	if (maxlen < size)
 		goto out_free;
-- 
1.8.3.2

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