From: Johannes Berg <johannes.berg@intel.com>
Date: Wed, 26 Sep 2018 11:15:34 +0200
Subject: [PATCH] netlink: add nested array policy validation
Patch-mainline: v4.20-rc1
Git-commit: 1501d13596b92d6d1f0ea5e104be838188b6e026
References: bsc#1152107 CVE-2019-16746
Sometimes nested netlink attributes are just used as arrays, with
the nla_type() of each not being used; we have this in nl80211 and
e.g. NFTA_SET_ELEM_LIST_ELEMENTS.
Add the ability to validate this type of message directly in the
policy, by adding the type NLA_NESTED_ARRAY which does exactly
this: require a first level of nesting but ignore the attribute
type, and then inside each require a second level of nested and
validate those attributes against a given policy (if present).
Note that some nested array types actually require that all of
the entries have the same index, this is possible to express in
a nested policy already, apart from the validation that only the
one allowed type is used.
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Cho, Yu-Chen <acho@suse.com>
---
include/net/netlink.h | 12 ++++++++++-
lib/nlattr.c | 51 ++++++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 62 insertions(+), 1 deletion(-)
--- a/include/net/netlink.h
+++ b/include/net/netlink.h
@@ -171,6 +171,7 @@ enum {
NLA_FLAG,
NLA_MSECS,
NLA_NESTED,
+ NLA_NESTED_ARRAY,
NLA_NESTED_COMPAT,
NLA_NUL_STRING,
NLA_BINARY,
@@ -198,7 +199,8 @@ enum {
* NLA_NUL_STRING Maximum length of string (excluding NUL)
* NLA_FLAG Unused
* NLA_BINARY Maximum length of attribute payload
- * NLA_NESTED Length verification is done by checking len of
+ * NLA_NESTED,
+ * NLA_NESTED_ARRAY 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.
@@ -225,6 +227,12 @@ enum {
* `len' to the max attribute number.
* Note that nla_parse() will validate, but of course not
* parse, the nested sub-policies.
+ * NLA_NESTED_ARRAY Points to a nested policy to validate, must also set
+ * `len' to the max attribute number. The difference to
+ * NLA_NESTED is the structure - NLA_NESTED has the
+ * nested attributes directly inside, while an array has
+ * the nested attributes at another level down and the
+ * attributes directly in the nesting don't matter.
* All other Unused
*
* Example:
@@ -243,6 +251,8 @@ struct nla_policy {
#define NLA_POLICY_NESTED(maxattr, policy) \
{ .type = NLA_NESTED, .validation_data = policy, .len = maxattr }
+#define NLA_POLICY_NESTED_ARRAY(maxattr, policy) \
+ { .type = NLA_NESTED_ARRAY, .validation_data = policy, .len = maxattr }
/**
* struct nl_info - netlink source information
--- a/lib/nlattr.c
+++ b/lib/nlattr.c
@@ -51,6 +51,34 @@ static int validate_nla_bitfield32(const
return 0;
}
+static int nla_validate_array(const struct nlattr *head, int len, int maxtype,
+ const struct nla_policy *policy,
+ struct netlink_ext_ack *extack)
+{
+ const struct nlattr *entry;
+ int rem;
+
+ nla_for_each_attr(entry, head, len, rem) {
+ int ret;
+
+ if (nla_len(entry) == 0)
+ continue;
+
+ if (nla_len(entry) < NLA_HDRLEN) {
+ NL_SET_ERR_MSG_ATTR(extack, entry,
+ "Array element too short");
+ return -ERANGE;
+ }
+
+ ret = nla_validate(nla_data(entry), nla_len(entry),
+ maxtype, policy, extack);
+ if (ret < 0)
+ return ret;
+ }
+
+ return 0;
+}
+
static int validate_nla(const struct nlattr *nla, int maxtype,
const struct nla_policy *policy,
struct netlink_ext_ack *extack)
@@ -147,6 +175,29 @@ static int validate_nla(const struct nla
if (err < 0) {
/*
* return directly to preserve the inner
+ * error message/attribute pointer
+ */
+ return err;
+ }
+ }
+ break;
+ case NLA_NESTED_ARRAY:
+ /* a nested array attribute is allowed to be empty; if its not,
+ * it must have a size of at least NLA_HDRLEN.
+ */
+ if (attrlen == 0)
+ break;
+ if (attrlen < NLA_HDRLEN)
+ goto out_err;
+ if (pt->validation_data) {
+ int err;
+
+ err = nla_validate_array(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;