netlink: add mask validation

We don't have good validation policy for existing unsigned int attrs
which serve as flags (for new ones we could use NLA_BITFIELD32).
With increased use of policy dumping having the validation be
expressed as part of the policy is important. Add validation
policy in form of a mask of supported/valid bits.

Support u64 in the uAPI to be future-proof, but really for now
the embedded mask member can only hold 32 bits, so anything with
bit 32+ set will always fail validation.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 36 insertions, 0 deletions

diff --git a/lib/nlattr.c b/lib/nlattr.c
index 80ff9fe83696..9c99f5daa4d2 100644
--- a/lib/nlattr.c
+++ b/lib/nlattr.c
@@ -323,6 +323,37 @@ static int nla_validate_int_range(const struct nla_policy *pt,
 	}
 }
 
+static int nla_validate_mask(const struct nla_policy *pt,
+			     const struct nlattr *nla,
+			     struct netlink_ext_ack *extack)
+{
+	u64 value;
+
+	switch (pt->type) {
+	case NLA_U8:
+		value = nla_get_u8(nla);
+		break;
+	case NLA_U16:
+		value = nla_get_u16(nla);
+		break;
+	case NLA_U32:
+		value = nla_get_u32(nla);
+		break;
+	case NLA_U64:
+		value = nla_get_u64(nla);
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	if (value & ~(u64)pt->mask) {
+		NL_SET_ERR_MSG_ATTR(extack, nla, "reserved bit set");
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
 static int validate_nla(const struct nlattr *nla, int maxtype,
 			const struct nla_policy *policy, unsigned int validate,
 			struct netlink_ext_ack *extack, unsigned int depth)
@@ -503,6 +534,11 @@ static int validate_nla(const struct nlattr *nla, int maxtype,
 		if (err)
 			return err;
 		break;
+	case NLA_VALIDATE_MASK:
+		err = nla_validate_mask(pt, nla, extack);
+		if (err)
+			return err;
+		break;
 	case NLA_VALIDATE_FUNCTION:
 		if (pt->validate) {
 			err = pt->validate(nla, extack);