path: root/net/ipv4/igmp.c
diff options
authorBenjamin Poirier <bpoirier@suse.com>2016-02-29 15:03:33 -0800
committerDavid S. Miller <davem@davemloft.net>2016-03-03 15:41:07 -0500
commit1837b2e2bcd23137766555a63867e649c0b637f0 (patch)
tree714cbf17e9e82a04b314fa4734f69b115f67918c /net/ipv4/igmp.c
parentfsl/fman: Initialize fman->dev earlier (diff)
mld, igmp: Fix reserved tailroom calculation
The current reserved_tailroom calculation fails to take hlen and tlen into account. skb: [__hlen__|__data____________|__tlen___|__extra__] ^ ^ head skb_end_offset In this representation, hlen + data + tlen is the size passed to alloc_skb. "extra" is the extra space made available in __alloc_skb because of rounding up by kmalloc. We can reorder the representation like so: [__hlen__|__data____________|__extra__|__tlen___] ^ ^ head skb_end_offset The maximum space available for ip headers and payload without fragmentation is min(mtu, data + extra). Therefore, reserved_tailroom = data + extra + tlen - min(mtu, data + extra) = skb_end_offset - hlen - min(mtu, skb_end_offset - hlen - tlen) = skb_tailroom - min(mtu, skb_tailroom - tlen) ; after skb_reserve(hlen) Compare the second line to the current expression: reserved_tailroom = skb_end_offset - min(mtu, skb_end_offset) and we can see that hlen and tlen are not taken into account. The min() in the third line can be expanded into: if mtu < skb_tailroom - tlen: reserved_tailroom = skb_tailroom - mtu else: reserved_tailroom = tlen Depending on hlen, tlen, mtu and the number of multicast address records, the current code may output skbs that have less tailroom than dev->needed_tailroom or it may output more skbs than needed because not all space available is used. Fixes: 4c672e4b ("ipv6: mld: fix add_grhead skb_over_panic for devs with large MTUs") Signed-off-by: Benjamin Poirier <bpoirier@suse.com> Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/ipv4/igmp.c')
1 files changed, 1 insertions, 2 deletions
diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c
index 05e4cba14162..b3086cf27027 100644
--- a/net/ipv4/igmp.c
+++ b/net/ipv4/igmp.c
@@ -356,9 +356,8 @@ static struct sk_buff *igmpv3_newpack(struct net_device *dev, unsigned int mtu)
skb_dst_set(skb, &rt->dst);
skb->dev = dev;
- skb->reserved_tailroom = skb_end_offset(skb) -
- min(mtu, skb_end_offset(skb));
skb_reserve(skb, hlen);
+ skb_tailroom_reserve(skb, mtu, tlen);
pip = ip_hdr(skb);