netlink: Avoid netlink mmap alloc if msg size exceeds frame size

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 <[email protected]>
Reviewed-by: Daniel Borkmann <[email protected]>
Signed-off-by: Jesse Gross <[email protected]>

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index bca50b95c182300cbd89f8cfc21b17e9d6e31fe2..64334893c61cc2d0530afa2f28bff044102b183a 100644 (file)
--- 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;