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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
parent878e3c1be2dc8a759c18bb280a7390f9ed0bd544 (diff)
downloadlinux-1837b2e2bcd23137766555a63867e649c0b637f0.tar.bz2
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>
-rw-r--r--include/linux/skbuff.h24
-rw-r--r--net/ipv4/igmp.c3
-rw-r--r--net/ipv6/mcast.c3
3 files changed, 26 insertions, 4 deletions
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 4ce9ff7086f4..d3fcd4591ce4 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -1985,6 +1985,30 @@ static inline void skb_reserve(struct sk_buff *skb, int len)
skb->tail += len;
}
+/**
+ * skb_tailroom_reserve - adjust reserved_tailroom
+ * @skb: buffer to alter
+ * @mtu: maximum amount of headlen permitted
+ * @needed_tailroom: minimum amount of reserved_tailroom
+ *
+ * Set reserved_tailroom so that headlen can be as large as possible but
+ * not larger than mtu and tailroom cannot be smaller than
+ * needed_tailroom.
+ * The required headroom should already have been reserved before using
+ * this function.
+ */
+static inline void skb_tailroom_reserve(struct sk_buff *skb, unsigned int mtu,
+ unsigned int needed_tailroom)
+{
+ SKB_LINEAR_ASSERT(skb);
+ if (mtu < skb_tailroom(skb) - needed_tailroom)
+ /* use at most mtu */
+ skb->reserved_tailroom = skb_tailroom(skb) - mtu;
+ else
+ /* use up to all available space */
+ skb->reserved_tailroom = needed_tailroom;
+}
+
#define ENCAP_TYPE_ETHER 0
#define ENCAP_TYPE_IPPROTO 1
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);
skb_reset_network_header(skb);
pip = ip_hdr(skb);
diff --git a/net/ipv6/mcast.c b/net/ipv6/mcast.c
index 5ee56d0a8699..d64ee7e83664 100644
--- a/net/ipv6/mcast.c
+++ b/net/ipv6/mcast.c
@@ -1574,9 +1574,8 @@ static struct sk_buff *mld_newpack(struct inet6_dev *idev, unsigned int mtu)
return NULL;
skb->priority = TC_PRIO_CONTROL;
- skb->reserved_tailroom = skb_end_offset(skb) -
- min(mtu, skb_end_offset(skb));
skb_reserve(skb, hlen);
+ skb_tailroom_reserve(skb, mtu, tlen);
if (__ipv6_get_lladdr(idev, &addr_buf, IFA_F_TENTATIVE)) {
/* <draft-ietf-magma-mld-source-05.txt>: