From: Johannes Berg <johannes.berg@xxxxxxxxx>
Now that we have a validation_data pointer, and the len field in
the policy is unused for NLA_NESTED, we can allow using them both
to have nested validation. This can be nice in code, although we
still have to use nla_parse_nested() or similar which would also
take a policy; however, it also serves as documentation in the
policy without requiring a look at the code.
Signed-off-by: Johannes Berg <johannes.berg@xxxxxxxxx>
---
include/net/netlink.h | 13 +++++++++++--
lib/nlattr.c | 14 ++++++++++++++
2 files changed, 25 insertions(+), 2 deletions(-)
diff --git a/include/net/netlink.h b/include/net/netlink.h
index 0d698215d4d9..91907852da1c 100644
--- a/include/net/netlink.h
+++ b/include/net/netlink.h
@@ -200,8 +200,10 @@ enum {
* NLA_NUL_STRING Maximum length of string (excluding NUL)
* NLA_FLAG Unused
* NLA_BINARY Maximum length of attribute payload
- * NLA_NESTED Don't use `len' field -- length verification is
- * done by checking len of nested header (or empty)
+ * NLA_NESTED Length verification is done by checking len of
+ * nested header (or empty); len field is used if
+ * validation_data is also used, for the max attr
+ * number in the nested policy.
* NLA_U8, NLA_U16,
* NLA_U32, NLA_U64,
* NLA_S8, NLA_S16,
@@ -224,6 +226,10 @@ enum {
* NLA_REJECT This attribute is always rejected and validation data
* may point to a string to report as the error instead
* of the generic one in extended ACK.
+ * NLA_NESTED Points to a nested policy to validate, must also set
+ * `len' to the max attribute number.
+ * Note that nla_parse() will validate, but of course not
+ * parse, the nested sub-policies.
* All other Unused
*
* Example:
@@ -247,6 +253,9 @@ struct nla_policy {
#define NLA_POLICY_ETH_ADDR NLA_POLICY_EXACT_LEN(ETH_ALEN)
#define NLA_POLICY_ETH_ADDR_COMPAT NLA_POLICY_EXACT_LEN_WARN(ETH_ALEN)
+#define NLA_POLICY_NESTED(maxattr, policy) \
+ { .type = NLA_NESTED, .validation_data = policy, .len = maxattr }
+
/**
* struct nl_info - netlink source information
* @nlh: Netlink message header of original request
diff --git a/lib/nlattr.c b/lib/nlattr.c
index ff6d48d7c19a..4cbfc64f6d10 100644
--- a/lib/nlattr.c
+++ b/lib/nlattr.c
@@ -152,6 +152,20 @@ static int validate_nla(const struct nlattr *nla, int maxtype,
*/
if (attrlen == 0)
break;
+ if (attrlen < NLA_HDRLEN)
+ goto out_err;
+ if (pt->validation_data) {
+ err = nla_validate(nla_data(nla), nla_len(nla), pt->len,
+ pt->validation_data, extack);
+ if (err < 0) {
+ /*
+ * return directly to preserve the inner
+ * error message/attribute pointer
+ */
+ return err;
+ }
+ }
+ break;
default:
if (pt->len)
minlen = pt->len;
--
2.14.4
