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>
diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c
index d5487c8..38d29b1 100644
--- a/net/ipv4/ip_sockglue.c
+++ b/net/ipv4/ip_sockglue.c
@@ -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.
*/
