[RFC PATCH v2 3/4] crypto: dh - allow user to provide NULL privkey

[Tudor Ambarus <tudor.ambarus@xxxxxxxxxxxxx>]

If the user provides a NULL private key, the kernel will
generate it and further use it for dh.

Signed-off-by: Tudor Ambarus <tudor.ambarus@xxxxxxxxxxxxx>
---
 crypto/dh.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/crypto/dh.c b/crypto/dh.c
index 87e3542..7b4ac5b 100644
--- a/crypto/dh.c
+++ b/crypto/dh.c
@@ -83,7 +83,9 @@ static int dh_set_secret(struct crypto_kpp *tfm, const void *buf,
 			 unsigned int len)
 {
 	struct dh_ctx *ctx = dh_get_ctx(tfm);
+	u8 *rndbuf = NULL;
 	struct dh params;
+	int maxsize;
 
 	if (crypto_dh_decode_key(buf, len, &params) < 0)
 		return -EINVAL;
@@ -91,7 +93,26 @@ static int dh_set_secret(struct crypto_kpp *tfm, const void *buf,
 	if (dh_set_params(ctx, &params) < 0)
 		return -EINVAL;
 
+	if (!params.key || !params.key_size) {
+		maxsize = crypto_kpp_maxsize(tfm);
+		if (maxsize < 0) {
+			dh_clear_params(ctx);
+			return maxsize;
+		}
+
+		rndbuf = kmalloc(maxsize, GFP_KERNEL);
+		if (!rndbuf) {
+			dh_clear_params(ctx);
+			return -ENOMEM;
+		}
+
+		get_random_bytes(rndbuf, maxsize);
+		params.key = rndbuf;
+		params.key_size = maxsize;
+	}
+
 	ctx->xa = mpi_read_raw_data(params.key, params.key_size);
+	kzfree(rndbuf);
 	if (!ctx->xa) {
 		dh_clear_params(ctx);
 		return -EINVAL;
-- 
2.7.4