seg6: Fix validation of nexthop addresses

The kernel currently validates that the length of the provided nexthop
address does not exceed the specified length. This can lead to the
kernel reading uninitialized memory if user space provided a shorter
length than the specified one.

Fix by validating that the provided length exactly matches the specified
one.

Fixes: d1df6fd ("ipv6: sr: define core operations for seg6local lightweight tunnel")
Reviewed-by: Petr Machata <[email protected]>
Signed-off-by: Ido Schimmel <[email protected]>
Reviewed-by: David Ahern <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: idosch

net/ipv6/seg6_local.c

@@ -1644,10 +1644,8 @@ static const struct nla_policy seg6_local_policy[SEG6_LOCAL_MAX + 1] = {
 	[SEG6_LOCAL_SRH]	= { .type = NLA_BINARY },
 	[SEG6_LOCAL_TABLE]	= { .type = NLA_U32 },
 	[SEG6_LOCAL_VRFTABLE]	= { .type = NLA_U32 },
-	[SEG6_LOCAL_NH4]	= { .type = NLA_BINARY,
-				    .len = sizeof(struct in_addr) },
-	[SEG6_LOCAL_NH6]	= { .type = NLA_BINARY,
-				    .len = sizeof(struct in6_addr) },
+	[SEG6_LOCAL_NH4]	= NLA_POLICY_EXACT_LEN(sizeof(struct in_addr)),
+	[SEG6_LOCAL_NH6]	= NLA_POLICY_EXACT_LEN(sizeof(struct in6_addr)),
 	[SEG6_LOCAL_IIF]	= { .type = NLA_U32 },
 	[SEG6_LOCAL_OIF]	= { .type = NLA_U32 },
 	[SEG6_LOCAL_BPF]	= { .type = NLA_NESTED },