netlink: add validation of NLA_F_NESTED flag

Add new validation flag NL_VALIDATE_NESTED which adds three consistency
checks of NLA_F_NESTED_FLAG:

  - the flag is set on attributes with NLA_NESTED{,_ARRAY} policy
  - the flag is not set on attributes with other policies except NLA_UNSPEC
  - the flag is set on attribute passed to nla_parse_nested()

Signed-off-by: Michal Kubecek <mkubecek@suse.cz>

v2: change error messages to mention NLA_F_NESTED explicitly
Reviewed-by: Johannes Berg <johannes@sipsolutions.net>
Reviewed-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 25 insertions, 1 deletions

diff --git a/include/net/netlink.h b/include/net/netlink.h
index 679f649748d4..395b4406f4b0 100644
--- a/include/net/netlink.h
+++ b/include/net/netlink.h
@@ -401,6 +401,8 @@ struct nl_info {
  *      are enforced going forward.
  * @NL_VALIDATE_STRICT_ATTRS: strict attribute policy parsing (e.g.
  *      U8, U16, U32 must have exact size, etc.)
+ * @NL_VALIDATE_NESTED: Check that NLA_F_NESTED is set for NLA_NESTED(_ARRAY)
+ *      and unset for other policies.
  */
 enum netlink_validation {
         NL_VALIDATE_LIBERAL = 0,
@@ -408,6 +410,7 @@ enum netlink_validation {
         NL_VALIDATE_MAXTYPE = BIT(1),
         NL_VALIDATE_UNSPEC = BIT(2),
         NL_VALIDATE_STRICT_ATTRS = BIT(3),
+        NL_VALIDATE_NESTED = BIT(4),
 };
 
 #define NL_VALIDATE_DEPRECATED_STRICT (NL_VALIDATE_TRAILING |\
@@ -415,7 +418,8 @@ enum netlink_validation {
 #define NL_VALIDATE_STRICT (NL_VALIDATE_TRAILING |\
                             NL_VALIDATE_MAXTYPE |\
                             NL_VALIDATE_UNSPEC |\
-                            NL_VALIDATE_STRICT_ATTRS)
+                            NL_VALIDATE_STRICT_ATTRS |\
+                            NL_VALIDATE_NESTED)
 
 int netlink_rcv_skb(struct sk_buff *skb,
                     int (*cb)(struct sk_buff *, struct nlmsghdr *,
@@ -1132,6 +1136,11 @@ static inline int nla_parse_nested(struct nlattr *tb[], int maxtype,
                                    const struct nla_policy *policy,
                                    struct netlink_ext_ack *extack)
 {
+        if (!(nla->nla_type & NLA_F_NESTED)) {
+                NL_SET_ERR_MSG_ATTR(extack, nla, "NLA_F_NESTED is missing");
+                return -EINVAL;
+        }
+
         return __nla_parse(tb, maxtype, nla_data(nla), nla_len(nla), policy,
                            NL_VALIDATE_STRICT, extack);
 }
diff --git a/lib/nlattr.c b/lib/nlattr.c
index adc919b32bf9..cace9b307781 100644
--- a/lib/nlattr.c
+++ b/lib/nlattr.c
@@ -184,6 +184,21 @@ static int validate_nla(const struct nlattr *nla, int maxtype,
                 }
         }
 
+        if (validate & NL_VALIDATE_NESTED) {
+                if ((pt->type == NLA_NESTED || pt->type == NLA_NESTED_ARRAY) &&
+                    !(nla->nla_type & NLA_F_NESTED)) {
+                        NL_SET_ERR_MSG_ATTR(extack, nla,
+                                            "NLA_F_NESTED is missing");
+                        return -EINVAL;
+                }
+                if (pt->type != NLA_NESTED && pt->type != NLA_NESTED_ARRAY &&
+                    pt->type != NLA_UNSPEC && (nla->nla_type & NLA_F_NESTED)) {
+                        NL_SET_ERR_MSG_ATTR(extack, nla,
+                                            "NLA_F_NESTED not expected");
+                        return -EINVAL;
+                }
+        }
+
         switch (pt->type) {
         case NLA_EXACT_LEN:
                 if (attrlen != pt->len)