[PATCH net 1/4] net: lwtunnel: accept RTA_ENCAP without NLA_F_NESTED

[Yuya Kusakabe <yuya.kusakabe@gmail.com>]

lwtunnel_fill_encap() dumps RTA_ENCAP without NLA_F_NESTED, and
"ip route restore" sends the routes saved by "ip route save" back to
the kernel unchanged.  rpl and ioam6 break on the same path:
lwtunnel_build_state() hands the restored RTA_ENCAP to their
build_state callbacks, which parse it with nla_parse_nested() and so
require the flag.  Restoring an rpl route fails as below, and an ioam6
route fails with the same error:

  # ip -6 route add 2001:db8:1::/64 encap rpl segs 2001:db8::2 dev dummy0
  # ip -6 route save 2001:db8:1::/64 > route.bin
  # ip -6 route del 2001:db8:1::/64
  # ip -6 route restore < route.bin
  Error: NLA_F_NESTED is missing.

Setting the flag in the dump is not an option: userspace that does not
mask it off the attribute type, such as parse_rtattr() in iproute2,
would no longer find RTA_ENCAP.

Add lwtunnel_nla_parse(), which validates the nested attributes
strictly but does not require the flag on RTA_ENCAP itself, and use it
in rpl and ioam6.  Switching them to nla_parse_nested_deprecated()
instead would also make them accept unknown attributes, which they have
rejected since they were added.

Fixes: a7a29f9c361f ("net: ipv6: add rpl sr tunnel")
Fixes: 3edede08ff37 ("ipv6: ioam: Support for IOAM injection with lwtunnels")
Assisted-by: LLM
Signed-off-by: Yuya Kusakabe <yuya.kusakabe@gmail.com>
---
 include/net/lwtunnel.h    | 27 +++++++++++++++++++++++++++
 net/ipv6/ioam6_iptunnel.c |  4 ++--
 net/ipv6/rpl_iptunnel.c   |  4 ++--
 3 files changed, 31 insertions(+), 4 deletions(-)

diff --git a/include/net/lwtunnel.h b/include/net/lwtunnel.h
index 26232f603e33..046978d6224c 100644
--- a/include/net/lwtunnel.h
+++ b/include/net/lwtunnel.h
@@ -6,6 +6,7 @@
 #include <linux/netdevice.h>
 #include <linux/skbuff.h>
 #include <linux/types.h>
+#include <net/netlink.h>
 #include <net/route.h>
 
 #define LWTUNNEL_HASH_BITS   7
@@ -37,6 +38,7 @@ struct lwtunnel_state {
 };
 
 struct lwtunnel_encap_ops {
+	/* encap may lack NLA_F_NESTED, parse it with lwtunnel_nla_parse() */
 	int (*build_state)(struct net *net, struct nlattr *encap,
 			   unsigned int family, const void *cfg,
 			   struct lwtunnel_state **ts,
@@ -53,6 +55,31 @@ struct lwtunnel_encap_ops {
 	struct module *owner;
 };
 
+/**
+ * lwtunnel_nla_parse - parse the attributes nested in an lwtunnel encap
+ * @tb: destination array with maxtype+1 elements
+ * @maxtype: maximum attribute type to be expected
+ * @nla: encap attribute passed to &lwtunnel_encap_ops.build_state, or an
+ *	attribute nested in it
+ * @policy: validation policy
+ * @extack: extended ACK report struct
+ *
+ * The encap attribute, and some of the attributes nested in it, have always
+ * been dumped without NLA_F_NESTED, and userspace such as "ip route restore"
+ * sends a dump back unchanged, so the flag cannot be required on @nla.
+ * The attributes nested in @nla are still validated strictly.
+ *
+ * Return: 0 on success or a negative error code.
+ */
+static inline int lwtunnel_nla_parse(struct nlattr *tb[], int maxtype,
+				     const struct nlattr *nla,
+				     const struct nla_policy *policy,
+				     struct netlink_ext_ack *extack)
+{
+	return nla_parse(tb, maxtype, nla_data(nla), nla_len(nla), policy,
+			 extack);
+}
+
 #ifdef CONFIG_LWTUNNEL
 
 DECLARE_STATIC_KEY_FALSE(nf_hooks_lwtunnel_enabled);
diff --git a/net/ipv6/ioam6_iptunnel.c b/net/ipv6/ioam6_iptunnel.c
index cfb2c41634a0..946c360ff214 100644
--- a/net/ipv6/ioam6_iptunnel.c
+++ b/net/ipv6/ioam6_iptunnel.c
@@ -113,8 +113,8 @@ static int ioam6_build_state(struct net *net, struct nlattr *nla,
 	if (family != AF_INET6)
 		return -EINVAL;
 
-	err = nla_parse_nested(tb, IOAM6_IPTUNNEL_MAX, nla,
-			       ioam6_iptunnel_policy, extack);
+	err = lwtunnel_nla_parse(tb, IOAM6_IPTUNNEL_MAX, nla,
+				 ioam6_iptunnel_policy, extack);
 	if (err < 0)
 		return err;
 
diff --git a/net/ipv6/rpl_iptunnel.c b/net/ipv6/rpl_iptunnel.c
index 4e10adcd70e8..1861af408bbc 100644
--- a/net/ipv6/rpl_iptunnel.c
+++ b/net/ipv6/rpl_iptunnel.c
@@ -78,8 +78,8 @@ static int rpl_build_state(struct net *net, struct nlattr *nla,
 	if (family != AF_INET6)
 		return -EINVAL;
 
-	err = nla_parse_nested(tb, RPL_IPTUNNEL_MAX, nla,
-			       rpl_iptunnel_policy, extack);
+	err = lwtunnel_nla_parse(tb, RPL_IPTUNNEL_MAX, nla,
+				 rpl_iptunnel_policy, extack);
 	if (err < 0)
 		return err;
 

-- 
2.50.1