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ipv4: guard IP_MINTTL with a static key 

RFC 5082 IP_MINTTL option is rarely used on hosts.

Add a static key to remove from TCP fast path useless code,
and potential cache line miss to fetch inet_sk(sk)->min_ttl

Note that once ip4_min_ttl static key has been enabled,
it stays enabled until next boot.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Eric Dumazet 2021-10-25 09:48:24 -07:00 committed by Jakub Kicinski
parent 14834c4f4e
commit 020e71a3cf
3 changed files with 20 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
include/net/ip.h
View File

@ -24,6 +24,7 @@
#include <linux/skbuff.h>
#include <linux/jhash.h>
#include <linux/sockptr.h>
#include <linux/static_key.h>
#include <net/inet_sock.h>
#include <net/route.h>
@ -750,6 +751,7 @@ void ip_cmsg_recv_offset(struct msghdr *msg, struct sock *sk,
struct sk_buff *skb, int tlen, int offset);
int ip_cmsg_send(struct sock *sk, struct msghdr *msg,
struct ipcm_cookie *ipc, bool allow_ipv6);
DECLARE_STATIC_KEY_FALSE(ip4_min_ttl);
int ip_setsockopt(struct sock *sk, int level, int optname, sockptr_t optval,
unsigned int optlen);
int ip_getsockopt(struct sock *sk, int level, int optname, char __user *optval,

6
net/ipv4/ip_sockglue.c
View File

@ -886,6 +886,8 @@ static int compat_ip_mcast_join_leave(struct sock *sk, int optname,
return ip_mc_leave_group(sk, &mreq);
}
DEFINE_STATIC_KEY_FALSE(ip4_min_ttl);
static int do_ip_setsockopt(struct sock *sk, int level, int optname,
sockptr_t optval, unsigned int optlen)
{
@ -1352,6 +1354,10 @@ static int do_ip_setsockopt(struct sock *sk, int level, int optname,
goto e_inval;
if (val < 0 || val > 255)
goto e_inval;
if (val)
static_branch_enable(&ip4_min_ttl);
/* tcp_v4_err() and tcp_v4_rcv() might read min_ttl
* while we are changint it.
*/

4
net/ipv4/tcp_ipv4.c
View File

@ -508,11 +508,13 @@ int tcp_v4_err(struct sk_buff *skb, u32 info)
if (sk->sk_state == TCP_CLOSE)
goto out;
if (static_branch_unlikely(&ip4_min_ttl)) {
/* min_ttl can be changed concurrently from do_ip_setsockopt() */
if (unlikely(iph->ttl < READ_ONCE(inet_sk(sk)->min_ttl))) {
__NET_INC_STATS(net, LINUX_MIB_TCPMINTTLDROP);
goto out;
}
}
tp = tcp_sk(sk);
/* XXX (TFO) - tp->snd_una should be ISN (tcp_create_openreq_child() */
@ -2070,11 +2072,13 @@ process:
}
}
if (static_branch_unlikely(&ip4_min_ttl)) {
/* min_ttl can be changed concurrently from do_ip_setsockopt() */
if (unlikely(iph->ttl < READ_ONCE(inet_sk(sk)->min_ttl))) {
__NET_INC_STATS(net, LINUX_MIB_TCPMINTTLDROP);
goto discard_and_relse;
}
}
if (!xfrm4_policy_check(sk, XFRM_POLICY_IN, skb))
goto discard_and_relse;