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ipv4: Create and use fib_compute_spec_dst() helper.

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The specific destination is the host we direct unicast replies to.
Usually this is the original packet source address, but if we are
responding to a multicast or broadcast packet we have to use something
different.

Specifically we must use the source address we would use if we were to
send a packet to the unicast source of the original packet.

The routing cache precomputes this value, but we want to remove that
precomputation because it creates a hard dependency on the expensive
rpfilter source address validation which we'd like to make cheaper.

There are only three places where this matters:

1) ICMP replies.

2) pktinfo CMSG

3) IP options

Now there will be no real users of rt->rt_spec_dst and we can simply
remove it altogether.

Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
David S. Miller 2012-06-28 03:59:11 -07:00
parent 70e7341673
commit 35ebf65e85
5 changed files with 49 additions and 16 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
include/net/ip_fib.h
View File

@ -230,6 +230,7 @@ extern struct fib_table *fib_get_table(struct net *net, u32 id);
/* Exported by fib_frontend.c */
extern const struct nla_policy rtm_ipv4_policy[];
extern void ip_fib_init(void);
extern __be32 fib_compute_spec_dst(struct sk_buff *skb);
extern int fib_validate_source(struct sk_buff *skb, __be32 src, __be32 dst,
u8 tos, int oif, struct net_device *dev,
__be32 *spec_dst, u32 *itag);

29
net/ipv4/fib_frontend.c
View File

@ -180,6 +180,35 @@ unsigned int inet_dev_addr_type(struct net *net, const struct net_device *dev,
}
EXPORT_SYMBOL(inet_dev_addr_type);
__be32 fib_compute_spec_dst(struct sk_buff *skb)
{
struct net_device *dev = skb->dev;
struct in_device *in_dev;
struct fib_result res;
struct flowi4 fl4;
struct net *net;
if (skb->pkt_type != PACKET_BROADCAST &&
skb->pkt_type != PACKET_MULTICAST)
return ip_hdr(skb)->daddr;
in_dev = __in_dev_get_rcu(dev);
BUG_ON(!in_dev);
fl4.flowi4_oif = 0;
fl4.flowi4_iif = 0;
fl4.daddr = ip_hdr(skb)->saddr;
fl4.saddr = ip_hdr(skb)->daddr;
fl4.flowi4_tos = RT_TOS(ip_hdr(skb)->tos);
fl4.flowi4_scope = RT_SCOPE_UNIVERSE;
fl4.flowi4_mark = IN_DEV_SRC_VMARK(in_dev) ? skb->mark : 0;
net = dev_net(dev);
if (!fib_lookup(net, &fl4, &res))
return FIB_RES_PREFSRC(net, res);
else
return inet_select_addr(dev, 0, RT_SCOPE_UNIVERSE);
}
/* Given (packet source, input interface) and optional (dst, oif, tos):
* - (main) check, that source is valid i.e. not broadcast or our local
* address.

6
net/ipv4/icmp.c
View File

@ -95,6 +95,7 @@
#include <net/checksum.h>
#include <net/xfrm.h>
#include <net/inet_common.h>
#include <net/ip_fib.h>
/*
* Build xmit assembly blocks
@ -333,7 +334,7 @@ static void icmp_reply(struct icmp_bxm *icmp_param, struct sk_buff *skb)
struct flowi4 fl4;
struct sock *sk;
struct inet_sock *inet;
__be32 daddr;
__be32 daddr, saddr;
if (ip_options_echo(&icmp_param->replyopts.opt.opt, skb))
return;
@ -347,6 +348,7 @@ static void icmp_reply(struct icmp_bxm *icmp_param, struct sk_buff *skb)
inet->tos = ip_hdr(skb)->tos;
daddr = ipc.addr = ip_hdr(skb)->saddr;
saddr = fib_compute_spec_dst(skb);
ipc.opt = NULL;
ipc.tx_flags = 0;
if (icmp_param->replyopts.opt.opt.optlen) {
@ -356,7 +358,7 @@ static void icmp_reply(struct icmp_bxm *icmp_param, struct sk_buff *skb)
}
memset(&fl4, 0, sizeof(fl4));
fl4.daddr = daddr;
fl4.saddr = rt->rt_spec_dst;
fl4.saddr = saddr;
fl4.flowi4_tos = RT_TOS(ip_hdr(skb)->tos);
fl4.flowi4_proto = IPPROTO_ICMP;
security_skb_classify_flow(skb, flowi4_to_flowi(&fl4));

22
net/ipv4/ip_options.c
View File

@ -27,6 +27,7 @@
#include <net/icmp.h>
#include <net/route.h>
#include <net/cipso_ipv4.h>
#include <net/ip_fib.h>
/*
* Write options to IP header, record destination address to
@ -104,7 +105,7 @@ int ip_options_echo(struct ip_options *dopt, struct sk_buff *skb)
sptr = skb_network_header(skb);
dptr = dopt->__data;
daddr = skb_rtable(skb)->rt_spec_dst;
daddr = fib_compute_spec_dst(skb);
if (sopt->rr) {
optlen = sptr[sopt->rr+1];
@ -250,15 +251,14 @@ void ip_options_fragment(struct sk_buff *skb)
int ip_options_compile(struct net *net,
struct ip_options *opt, struct sk_buff *skb)
{
int l;
unsigned char *iph;
unsigned char *optptr;
int optlen;
__be32 spec_dst = (__force __be32) 0;
unsigned char *pp_ptr = NULL;
struct rtable *rt = NULL;
unsigned char *optptr;
unsigned char *iph;
int optlen, l;
if (skb != NULL) {
rt = skb_rtable(skb);
spec_dst = fib_compute_spec_dst(skb);
optptr = (unsigned char *)&(ip_hdr(skb)[1]);
} else
optptr = opt->__data;
@ -330,8 +330,8 @@ int ip_options_compile(struct net *net,
pp_ptr = optptr + 2;
goto error;
}
if (rt) {
memcpy(&optptr[optptr[2]-1], &rt->rt_spec_dst, 4);
if (skb) {
memcpy(&optptr[optptr[2]-1], &spec_dst, 4);
opt->is_changed = 1;
}
optptr[2] += 4;
@ -372,8 +372,8 @@ int ip_options_compile(struct net *net,
goto error;
}
opt->ts = optptr - iph;
if (rt) {
memcpy(&optptr[optptr[2]-1], &rt->rt_spec_dst, 4);
if (skb) {
memcpy(&optptr[optptr[2]-1], &spec_dst, 4);
timeptr = &optptr[optptr[2]+3];
}
opt->ts_needaddr = 1;

7
net/ipv4/ip_sockglue.c
View File

@ -40,6 +40,7 @@
#if IS_ENABLED(CONFIG_IPV6)
#include <net/transp_v6.h>
#endif
#include <net/ip_fib.h>
#include <linux/errqueue.h>
#include <asm/uaccess.h>
@ -1019,8 +1020,8 @@ e_inval:
* @sk: socket
* @skb: buffer
*
* To support IP_CMSG_PKTINFO option, we store rt_iif and rt_spec_dst
* in skb->cb[] before dst drop.
* To support IP_CMSG_PKTINFO option, we store rt_iif and specific
* destination in skb->cb[] before dst drop.
* This way, receiver doesnt make cache line misses to read rtable.
*/
void ipv4_pktinfo_prepare(struct sk_buff *skb)
@ -1030,7 +1031,7 @@ void ipv4_pktinfo_prepare(struct sk_buff *skb)
if (rt) {
pktinfo->ipi_ifindex = rt->rt_iif;
pktinfo->ipi_spec_dst.s_addr = rt->rt_spec_dst;
pktinfo->ipi_spec_dst.s_addr = fib_compute_spec_dst(skb);
} else {
pktinfo->ipi_ifindex = 0;
pktinfo->ipi_spec_dst.s_addr = 0;