diff options
| author | Benjamin Poirier <bpoirier@suse.com> | 2016-02-29 15:03:33 -0800 |
|---|---|---|
| committer | Sasha Levin <sasha.levin@oracle.com> | 2016-07-10 23:07:00 -0400 |
| commit | fda740f68c700b1da33a512ec8005d86f275265a (patch) | |
| tree | d3714f7757985ef2e19b0490d3b6305f5f751b1d /net/ipv4 | |
| parent | 67eab3249eacc0861cf57f6d929e66bf78159379 (diff) | |
mld, igmp: Fix reserved tailroom calculation
[ Upstream commit 1837b2e2bcd23137766555a63867e649c0b637f0 ]
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>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
Diffstat (limited to 'net/ipv4')
| -rw-r--r-- | net/ipv4/igmp.c | 3 |
1 files changed, 1 insertions, 2 deletions
diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c index a3a697f5ffba..218abf9fb1ed 100644 --- a/net/ipv4/igmp.c +++ b/net/ipv4/igmp.c @@ -353,9 +353,8 @@ 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); skb_reset_network_header(skb); pip = ip_hdr(skb); |