From feb91a02ccb09661507f170b2a444aec94f307f9 Mon Sep 17 00:00:00 2001 From: Daniel Borkmann Date: Wed, 5 Nov 2014 20:27:38 +0100 Subject: [PATCH] ipv6: mld: fix add_grhead skb_over_panic for devs with large MTUs It has been reported that generating an MLD listener report on devices with large MTUs (e.g. 9000) and a high number of IPv6 addresses can trigger a skb_over_panic(): skbuff: skb_over_panic: text:ffffffff80612a5d len:3776 put:20 head:ffff88046d751000 data:ffff88046d751010 tail:0xed0 end:0xec0 dev:port1 ------------[ cut here ]------------ kernel BUG at net/core/skbuff.c:100! invalid opcode: 0000 [#1] SMP Modules linked in: ixgbe(O) CPU: 3 PID: 0 Comm: swapper/3 Tainted: G O 3.14.23+ #4 [...] Call Trace: [] ? skb_put+0x3a/0x3b [] ? add_grhead+0x45/0x8e [] ? add_grec+0x394/0x3d4 [] ? mld_ifc_timer_expire+0x195/0x20d [] ? mld_dad_timer_expire+0x45/0x45 [] ? call_timer_fn.isra.29+0x12/0x68 [] ? run_timer_softirq+0x163/0x182 [] ? __do_softirq+0xe0/0x21d [] ? irq_exit+0x4e/0xd3 [] ? smp_apic_timer_interrupt+0x3b/0x46 [] ? apic_timer_interrupt+0x6a/0x70 mld_newpack() skb allocations are usually requested with dev->mtu in size, since commit 72e09ad107e7 ("ipv6: avoid high order allocations") we have changed the limit in order to be less likely to fail. However, in MLD/IGMP code, we have some rather ugly AVAILABLE(skb) macros, which determine if we may end up doing an skb_put() for adding another record. To avoid possible fragmentation, we check the skb's tailroom as skb->dev->mtu - skb->len, which is a wrong assumption as the actual max allocation size can be much smaller. The IGMP case doesn't have this issue as commit 57e1ab6eaddc ("igmp: refine skb allocations") stores the allocation size in the cb[]. Set a reserved_tailroom to make it fit into the MTU and use skb_availroom() helper instead. This also allows to get rid of igmp_skb_size(). Reported-by: Wei Liu Fixes: 72e09ad107e7 ("ipv6: avoid high order allocations") Signed-off-by: Daniel Borkmann Cc: Eric Dumazet Cc: Hannes Frederic Sowa Cc: David L Stevens Acked-by: Eric Dumazet Acked-by: Hannes Frederic Sowa Signed-off-by: David S. Miller --- net/ipv4/igmp.c | 11 +++++------ net/ipv6/mcast.c | 9 +++++---- 2 files changed, 10 insertions(+), 10 deletions(-) diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c index fb70e3e..bb15d0e 100644 --- a/net/ipv4/igmp.c +++ b/net/ipv4/igmp.c @@ -318,9 +318,7 @@ igmp_scount(struct ip_mc_list *pmc, int type, int gdeleted, int sdeleted) return scount; } -#define igmp_skb_size(skb) (*(unsigned int *)((skb)->cb)) - -static struct sk_buff *igmpv3_newpack(struct net_device *dev, int size) +static struct sk_buff *igmpv3_newpack(struct net_device *dev, unsigned int mtu) { struct sk_buff *skb; struct rtable *rt; @@ -330,6 +328,7 @@ static struct sk_buff *igmpv3_newpack(struct net_device *dev, int size) struct flowi4 fl4; int hlen = LL_RESERVED_SPACE(dev); int tlen = dev->needed_tailroom; + unsigned int size = mtu; while (1) { skb = alloc_skb(size + hlen + tlen, @@ -341,7 +340,6 @@ static struct sk_buff *igmpv3_newpack(struct net_device *dev, int size) return NULL; } skb->priority = TC_PRIO_CONTROL; - igmp_skb_size(skb) = size; rt = ip_route_output_ports(net, &fl4, NULL, IGMPV3_ALL_MCR, 0, 0, 0, @@ -354,6 +352,8 @@ static struct sk_buff *igmpv3_newpack(struct net_device *dev, int size) 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_reset_network_header(skb); @@ -423,8 +423,7 @@ static struct sk_buff *add_grhead(struct sk_buff *skb, struct ip_mc_list *pmc, return skb; } -#define AVAILABLE(skb) ((skb) ? ((skb)->dev ? igmp_skb_size(skb) - (skb)->len : \ - skb_tailroom(skb)) : 0) +#define AVAILABLE(skb) ((skb) ? skb_availroom(skb) : 0) static struct sk_buff *add_grec(struct sk_buff *skb, struct ip_mc_list *pmc, int type, int gdeleted, int sdeleted) diff --git a/net/ipv6/mcast.c b/net/ipv6/mcast.c index 9648de2..ed2c4e4 100644 --- a/net/ipv6/mcast.c +++ b/net/ipv6/mcast.c @@ -1550,7 +1550,7 @@ static void ip6_mc_hdr(struct sock *sk, struct sk_buff *skb, hdr->daddr = *daddr; } -static struct sk_buff *mld_newpack(struct inet6_dev *idev, int size) +static struct sk_buff *mld_newpack(struct inet6_dev *idev, unsigned int mtu) { struct net_device *dev = idev->dev; struct net *net = dev_net(dev); @@ -1561,13 +1561,13 @@ static struct sk_buff *mld_newpack(struct inet6_dev *idev, int size) const struct in6_addr *saddr; int hlen = LL_RESERVED_SPACE(dev); int tlen = dev->needed_tailroom; + unsigned int size = mtu + hlen + tlen; int err; u8 ra[8] = { IPPROTO_ICMPV6, 0, IPV6_TLV_ROUTERALERT, 2, 0, 0, IPV6_TLV_PADN, 0 }; /* we assume size > sizeof(ra) here */ - size += hlen + tlen; /* limit our allocations to order-0 page */ size = min_t(int, size, SKB_MAX_ORDER(0, 0)); skb = sock_alloc_send_skb(sk, size, 1, &err); @@ -1576,6 +1576,8 @@ static struct sk_buff *mld_newpack(struct inet6_dev *idev, int size) return NULL; skb->priority = TC_PRIO_CONTROL; + skb->reserved_tailroom = skb_end_offset(skb) - + min(mtu, skb_end_offset(skb)); skb_reserve(skb, hlen); if (__ipv6_get_lladdr(idev, &addr_buf, IFA_F_TENTATIVE)) { @@ -1690,8 +1692,7 @@ static struct sk_buff *add_grhead(struct sk_buff *skb, struct ifmcaddr6 *pmc, return skb; } -#define AVAILABLE(skb) ((skb) ? ((skb)->dev ? (skb)->dev->mtu - (skb)->len : \ - skb_tailroom(skb)) : 0) +#define AVAILABLE(skb) ((skb) ? skb_availroom(skb) : 0) static struct sk_buff *add_grec(struct sk_buff *skb, struct ifmcaddr6 *pmc, int type, int gdeleted, int sdeleted, int crsend) -- 2.7.4