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>

1 files changed, 15 insertions, 0 deletions

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)