1 files changed, 63 insertions, 3 deletions

diff --git a/crypto/dh.c b/crypto/dh.c
index 5659fe7f446d..8f79269db2b7 100644
--- a/crypto/dh.c
+++ b/crypto/dh.c
@@ -16,14 +16,16 @@
 #include <linux/mpi.h>
 
 struct dh_ctx {
-	MPI p;
-	MPI g;
-	MPI xa;
+	MPI p;	/* Value is guaranteed to be set. */
+	MPI q;	/* Value is optional. */
+	MPI g;	/* Value is guaranteed to be set. */
+	MPI xa;	/* Value is guaranteed to be set. */
 };
 
 static void dh_clear_ctx(struct dh_ctx *ctx)
 {
 	mpi_free(ctx->p);
+	mpi_free(ctx->q);
 	mpi_free(ctx->g);
 	mpi_free(ctx->xa);
 	memset(ctx, 0, sizeof(*ctx));
@@ -60,6 +62,12 @@ static int dh_set_params(struct dh_ctx *ctx, struct dh *params)
 	if (!ctx->p)
 		return -EINVAL;
 
+	if (params->q && params->q_size) {
+		ctx->q = mpi_read_raw_data(params->q, params->q_size);
+		if (!ctx->q)
+			return -EINVAL;
+	}
+
 	ctx->g = mpi_read_raw_data(params->g, params->g_size);
 	if (!ctx->g)
 		return -EINVAL;
@@ -93,6 +101,55 @@ err_clear_ctx:
 	return -EINVAL;
 }
 
+/*
+ * SP800-56A public key verification:
+ *
+ * * If Q is provided as part of the domain paramenters, a full validation
+ *   according to SP800-56A section 5.6.2.3.1 is performed.
+ *
+ * * If Q is not provided, a partial validation according to SP800-56A section
+ *   5.6.2.3.2 is performed.
+ */
+static int dh_is_pubkey_valid(struct dh_ctx *ctx, MPI y)
+{
+	if (unlikely(!ctx->p))
+		return -EINVAL;
+
+	/*
+	 * Step 1: Verify that 2 <= y <= p - 2.
+	 *
+	 * The upper limit check is actually y < p instead of y < p - 1
+	 * as the mpi_sub_ui function is yet missing.
+	 */
+	if (mpi_cmp_ui(y, 1) < 1 || mpi_cmp(y, ctx->p) >= 0)
+		return -EINVAL;
+
+	/* Step 2: Verify that 1 = y^q mod p */
+	if (ctx->q) {
+		MPI val = mpi_alloc(0);
+		int ret;
+
+		if (!val)
+			return -ENOMEM;
+
+		ret = mpi_powm(val, y, ctx->q, ctx->p);
+
+		if (ret) {
+			mpi_free(val);
+			return ret;
+		}
+
+		ret = mpi_cmp_ui(val, 1);
+
+		mpi_free(val);
+
+		if (ret != 0)
+			return -EINVAL;
+	}
+
+	return 0;
+}
+
 static int dh_compute_value(struct kpp_request *req)
 {
 	struct crypto_kpp *tfm = crypto_kpp_reqtfm(req);
@@ -115,6 +172,9 @@ static int dh_compute_value(struct kpp_request *req)
 			ret = -EINVAL;
 			goto err_free_val;
 		}
+		ret = dh_is_pubkey_valid(ctx, base);
+		if (ret)
+			goto err_free_val;
 	} else {
 		base = ctx->g;
 	}