net: change accept_ra_min_rtr_lft to affect all RA lifetimes

accept_ra_min_rtr_lft only considered the lifetime of the default route
and discarded entire RAs accordingly.

This change renames accept_ra_min_rtr_lft to accept_ra_min_lft, and
applies the value to individual RA sections; in particular, router
lifetime, PIO preferred lifetime, and RIO lifetime. If any of those
lifetimes are lower than the configured value, the specific RA section
is ignored.

In order for the sysctl to be useful to Android, it should really apply
to all lifetimes in the RA, since that is what determines the minimum
frequency at which RAs must be processed by the kernel. Android uses
hardware offloads to drop RAs for a fraction of the minimum of all
lifetimes present in the RA (some networks have very frequent RAs (5s)
with high lifetimes (2h)). Despite this, we have encountered networks
that set the router lifetime to 30s which results in very frequent CPU
wakeups. Instead of disabling IPv6 (and dropping IPv6 ethertype in the
WiFi firmware) entirely on such networks, it seems better to ignore the
misconfigured routers while still processing RAs from other IPv6 routers
on the same network (i.e. to support IoT applications).

The previous implementation dropped the entire RA based on router
lifetime. This turned out to be hard to expand to the other lifetimes
present in the RA in a consistent manner; dropping the entire RA based
on RIO/PIO lifetimes would essentially require parsing the whole thing
twice.

Fixes: 1671bcfd76fd ("net: add sysctl accept_ra_min_rtr_lft")
Cc: Lorenzo Colitti <lorenzo@google.com>
Signed-off-by: Patrick Rohr <prohr@google.com>
Reviewed-by: Maciej Żenczykowski <maze@google.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://lore.kernel.org/r/20230726230701.919212-1-prohr@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 11 insertions, 16 deletions

diff --git a/net/ipv6/ndisc.c b/net/ipv6/ndisc.c
index 95750fbf6782..c394799be38f 100644
--- a/net/ipv6/ndisc.c
+++ b/net/ipv6/ndisc.c
@@ -1276,8 +1276,6 @@ static enum skb_drop_reason ndisc_router_discovery(struct sk_buff *skb)
 	if (!ndisc_parse_options(skb->dev, opt, optlen, &ndopts))
 		return SKB_DROP_REASON_IPV6_NDISC_BAD_OPTIONS;
 
-	lifetime = ntohs(ra_msg->icmph.icmp6_rt_lifetime);
-
 	if (!ipv6_accept_ra(in6_dev)) {
 		ND_PRINTK(2, info,
 			  "RA: %s, did not accept ra for dev: %s\n",
@@ -1285,13 +1283,6 @@ static enum skb_drop_reason ndisc_router_discovery(struct sk_buff *skb)
 		goto skip_linkparms;
 	}
 
-	if (lifetime != 0 && lifetime < in6_dev->cnf.accept_ra_min_rtr_lft) {
-		ND_PRINTK(2, info,
-			  "RA: router lifetime (%ds) is too short: %s\n",
-			  lifetime, skb->dev->name);
-		goto skip_linkparms;
-	}
-
 #ifdef CONFIG_IPV6_NDISC_NODETYPE
 	/* skip link-specific parameters from interior routers */
 	if (skb->ndisc_nodetype == NDISC_NODETYPE_NODEFAULT) {
@@ -1332,6 +1323,14 @@ static enum skb_drop_reason ndisc_router_discovery(struct sk_buff *skb)
 		goto skip_defrtr;
 	}
 
+	lifetime = ntohs(ra_msg->icmph.icmp6_rt_lifetime);
+	if (lifetime != 0 && lifetime < in6_dev->cnf.accept_ra_min_lft) {
+		ND_PRINTK(2, info,
+			  "RA: router lifetime (%ds) is too short: %s\n",
+			  lifetime, skb->dev->name);
+		goto skip_defrtr;
+	}
+
 	/* Do not accept RA with source-addr found on local machine unless
 	 * accept_ra_from_local is set to true.
 	 */
@@ -1495,13 +1494,6 @@ skip_linkparms:
 		goto out;
 	}
 
-	if (lifetime != 0 && lifetime < in6_dev->cnf.accept_ra_min_rtr_lft) {
-		ND_PRINTK(2, info,
-			  "RA: router lifetime (%ds) is too short: %s\n",
-			  lifetime, skb->dev->name);
-		goto out;
-	}
-
 #ifdef CONFIG_IPV6_ROUTE_INFO
 	if (!in6_dev->cnf.accept_ra_from_local &&
 	    ipv6_chk_addr(dev_net(in6_dev->dev), &ipv6_hdr(skb)->saddr,
@@ -1526,6 +1518,9 @@ skip_linkparms:
 			if (ri->prefix_len == 0 &&
 			    !in6_dev->cnf.accept_ra_defrtr)
 				continue;
+			if (ri->lifetime != 0 &&
+			    ntohl(ri->lifetime) < in6_dev->cnf.accept_ra_min_lft)
+				continue;
 			if (ri->prefix_len < in6_dev->cnf.accept_ra_rt_info_min_plen)
 				continue;
 			if (ri->prefix_len > in6_dev->cnf.accept_ra_rt_info_max_plen)