[PATCH net v3 3/6] amt: reject an IPv6 address passed in an IPv4 address attribute

[Omar Ramadan <omar@blockcast.net>]

The netlink policy for IFLA_AMT_LOCAL_IP and IFLA_AMT_DISCOVERY_IP sets
only a minimum length (the size of an IPv4 address), so an iproute2 that
puts a 16-byte IPv6 literal in one of these IPv4 attributes passes
validation.  nla_get_in_addr() then reads just the first four bytes, so
"2001:db8::" silently becomes 32.1.13.184 and the device is created with an
address the user never asked for.

Reject an attribute whose length is exactly an IPv6 address for the two
IPv4 attributes, so the mistake is refused with an extack instead of being
truncated.

Fixes: b9022b53adad ("amt: add control plane of amt interface")
Assisted-by: LLM
Signed-off-by: Omar Ramadan <omar@blockcast.net>
---
 drivers/net/amt.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/drivers/net/amt.c b/drivers/net/amt.c
index c3716ba..550b0a5 100644
--- a/drivers/net/amt.c
+++ b/drivers/net/amt.c
@@ -3194,6 +3194,15 @@ static const struct nla_policy amt_policy[IFLA_AMT_MAX + 1] = {
 	[IFLA_AMT_MAX_TUNNELS]	= { .type = NLA_U32 },
 };
 
+static bool amt_ip6_in_ip4_attr(const struct nlattr *attr,
+				struct netlink_ext_ack *extack)
+{
+	if (!attr || nla_len(attr) != sizeof(struct in6_addr))
+		return false;
+	NL_SET_ERR_MSG_ATTR(extack, attr, "IPv6 address in an IPv4 attribute");
+	return true;
+}
+
 static int amt_validate(struct nlattr *tb[], struct nlattr *data[],
 			struct netlink_ext_ack *extack)
 {
@@ -3224,6 +3233,9 @@ static int amt_validate(struct nlattr *tb[], struct nlattr *data[],
 		return -EINVAL;
 	}
 
+	if (amt_ip6_in_ip4_attr(data[IFLA_AMT_LOCAL_IP], extack))
+		return -EINVAL;
+
 	if (!data[IFLA_AMT_DISCOVERY_IP] &&
 	    nla_get_u32(data[IFLA_AMT_MODE]) == AMT_MODE_GATEWAY) {
 		NL_SET_ERR_MSG_ATTR(extack, data[IFLA_AMT_LOCAL_IP],
@@ -3231,6 +3243,9 @@ static int amt_validate(struct nlattr *tb[], struct nlattr *data[],
 		return -EINVAL;
 	}
 
+	if (amt_ip6_in_ip4_attr(data[IFLA_AMT_DISCOVERY_IP], extack))
+		return -EINVAL;
+
 	return 0;
 }
 
-- 
2.43.0