[PATCH 6.1] net: add sysctl accept_ra_min_lft

[PATCH 6.1] net: add sysctl accept_ra_min_lft

[Patrick Rohr]

This change adds a new sysctl accept_ra_min_lft which enforces a minimum
lifetime value for 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.

This fixes a potential denial of service attack vector where rogue WiFi
routers (or devices) can send RAs with low lifetimes to actively drain a
mobile device's battery (by preventing sleep).

In addition to this change, 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, misconfigured routers must be ignored while still processing
RAs from other IPv6 routers on the same network (i.e. to support IoT
applications).

This change squashes the following patches into a single commit:
- net-next 1671bcfd76fd ("net: add sysctl accept_ra_min_rtr_lft")
- net-next 5027d54a9c30 ("net: change accept_ra_min_rtr_lft to affect all RA lifetimes")
- net-next 5cb249686e67 ("net: release reference to inet6_dev pointer")

Cc: Maciej Żenczykowski <maze@google.com>
Cc: Lorenzo Colitti <lorenzo@google.com>
Signed-off-by: Patrick Rohr <prohr@google.com>
---
 Documentation/networking/ip-sysctl.rst |  8 ++++++++
 include/linux/ipv6.h                   |  1 +
 include/uapi/linux/ipv6.h              |  1 +
 net/ipv6/addrconf.c                    | 13 +++++++++++++
 net/ipv6/ndisc.c                       | 13 +++++++++++--
 5 files changed, 34 insertions(+), 2 deletions(-)

diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst
index 3301288a7c69..f5f7a464605f 100644
--- a/Documentation/networking/ip-sysctl.rst
+++ b/Documentation/networking/ip-sysctl.rst
@@ -2148,6 +2148,14 @@ accept_ra_min_hop_limit - INTEGER
 
 	Default: 1
 
+accept_ra_min_lft - INTEGER
+	Minimum acceptable lifetime value in Router Advertisement.
+
+	RA sections with a lifetime less than this value shall be
+	ignored. Zero lifetimes stay unaffected.
+
+	Default: 0
+
 accept_ra_pinfo - BOOLEAN
 	Learn Prefix Information in Router Advertisement.
 
diff --git a/include/linux/ipv6.h b/include/linux/ipv6.h
index 37dfdcfcdd54..0e3c95055b21 100644
--- a/include/linux/ipv6.h
+++ b/include/linux/ipv6.h
@@ -33,6 +33,7 @@ struct ipv6_devconf {
 	__s32		accept_ra_defrtr;
 	__u32		ra_defrtr_metric;
 	__s32		accept_ra_min_hop_limit;
+	__s32		accept_ra_min_lft;
 	__s32		accept_ra_pinfo;
 	__s32		ignore_routes_with_linkdown;
 #ifdef CONFIG_IPV6_ROUTER_PREF
diff --git a/include/uapi/linux/ipv6.h b/include/uapi/linux/ipv6.h
index 53326dfc59ec..4fa8511b1e35 100644
--- a/include/uapi/linux/ipv6.h
+++ b/include/uapi/linux/ipv6.h
@@ -198,6 +198,7 @@ enum {
 	DEVCONF_IOAM6_ID_WIDE,
 	DEVCONF_NDISC_EVICT_NOCARRIER,
 	DEVCONF_ACCEPT_UNTRACKED_NA,
+	DEVCONF_ACCEPT_RA_MIN_LFT,
 	DEVCONF_MAX
 };
 
diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 48a6486951cd..5480ee507c61 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -202,6 +202,7 @@ static struct ipv6_devconf ipv6_devconf __read_mostly = {
 	.ra_defrtr_metric	= IP6_RT_PRIO_USER,
 	.accept_ra_from_local	= 0,
 	.accept_ra_min_hop_limit= 1,
+	.accept_ra_min_lft	= 0,
 	.accept_ra_pinfo	= 1,
 #ifdef CONFIG_IPV6_ROUTER_PREF
 	.accept_ra_rtr_pref	= 1,
@@ -262,6 +263,7 @@ static struct ipv6_devconf ipv6_devconf_dflt __read_mostly = {
 	.ra_defrtr_metric	= IP6_RT_PRIO_USER,
 	.accept_ra_from_local	= 0,
 	.accept_ra_min_hop_limit= 1,
+	.accept_ra_min_lft	= 0,
 	.accept_ra_pinfo	= 1,
 #ifdef CONFIG_IPV6_ROUTER_PREF
 	.accept_ra_rtr_pref	= 1,
@@ -2731,6 +2733,9 @@ void addrconf_prefix_rcv(struct net_device *dev, u8 *opt, int len, bool sllao)
 		return;
 	}
 
+	if (valid_lft != 0 && valid_lft < in6_dev->cnf.accept_ra_min_lft)
+		goto put;
+
 	/*
 	 *	Two things going on here:
 	 *	1) Add routes for on-link prefixes
@@ -5601,6 +5606,7 @@ static inline void ipv6_store_devconf(struct ipv6_devconf *cnf,
 	array[DEVCONF_IOAM6_ID_WIDE] = cnf->ioam6_id_wide;
 	array[DEVCONF_NDISC_EVICT_NOCARRIER] = cnf->ndisc_evict_nocarrier;
 	array[DEVCONF_ACCEPT_UNTRACKED_NA] = cnf->accept_untracked_na;
+	array[DEVCONF_ACCEPT_RA_MIN_LFT] = cnf->accept_ra_min_lft;
 }
 
 static inline size_t inet6_ifla6_size(void)
@@ -6794,6 +6800,13 @@ static const struct ctl_table addrconf_sysctl[] = {
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec,
 	},
+	{
+		.procname	= "accept_ra_min_lft",
+		.data		= &ipv6_devconf.accept_ra_min_lft,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec,
+	},
 	{
 		.procname	= "accept_ra_pinfo",
 		.data		= &ipv6_devconf.accept_ra_pinfo,
diff --git a/net/ipv6/ndisc.c b/net/ipv6/ndisc.c
index a4d43eb45a9d..6cb2d6a536a8 100644
--- a/net/ipv6/ndisc.c
+++ b/net/ipv6/ndisc.c
@@ -1331,6 +1331,14 @@ static void 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.
 	 */
@@ -1343,8 +1351,6 @@ static void ndisc_router_discovery(struct sk_buff *skb)
 		goto skip_defrtr;
 	}
 
-	lifetime = ntohs(ra_msg->icmph.icmp6_rt_lifetime);
-
 #ifdef CONFIG_IPV6_ROUTER_PREF
 	pref = ra_msg->icmph.icmp6_router_pref;
 	/* 10b is handled as if it were 00b (medium) */
@@ -1519,6 +1525,9 @@ static void ndisc_router_discovery(struct sk_buff *skb)
 			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)
-- 
2.42.0.rc1.204.g551eb34607-goog

Re: [PATCH 6.1] net: add sysctl accept_ra_min_lft

[Greg KH]

On Thu, Aug 24, 2023 at 03:32:25PM -0700, Patrick Rohr wrote:
> This change adds a new sysctl accept_ra_min_lft which enforces a minimum
> lifetime value for 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.
> 
> This fixes a potential denial of service attack vector where rogue WiFi
> routers (or devices) can send RAs with low lifetimes to actively drain a
> mobile device's battery (by preventing sleep).
> 
> In addition to this change, 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, misconfigured routers must be ignored while still processing
> RAs from other IPv6 routers on the same network (i.e. to support IoT
> applications).
> 
> This change squashes the following patches into a single commit:
> - net-next 1671bcfd76fd ("net: add sysctl accept_ra_min_rtr_lft")
> - net-next 5027d54a9c30 ("net: change accept_ra_min_rtr_lft to affect all RA lifetimes")
> - net-next 5cb249686e67 ("net: release reference to inet6_dev pointer")

Please don't do this.  We want the original commits into the stable
tree, after they have landed in Linus's tree.

Please read:
    https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to do this properly.

thanks,

greg k-h