crypto: sm2 - Fix crash caused by uninitialized context

In sm2_compute_z_digest() function, the newly allocated structure
mpi_ec_ctx is used, but forget to initialize it, which will cause
a crash when performing subsequent operations.

Fixes: e5221fa ("KEYS: asymmetric: Move sm2 code into x509_public_key")
Cc: stable@vger.kernel.org # v6.5
Signed-off-by: Tianjia Zhang <tianjia.zhang@linux.alibaba.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/sm2.c

@@ -278,10 +278,14 @@ int sm2_compute_z_digest(struct shash_desc *desc,
 	if (!ec)
 		return -ENOMEM;
 
-	err = __sm2_set_pub_key(ec, key, keylen);
+	err = sm2_ec_ctx_init(ec);
 	if (err)
 		goto out_free_ec;
 
+	err = __sm2_set_pub_key(ec, key, keylen);
+	if (err)
+		goto out_deinit_ec;
+
 	bits_len = SM2_DEFAULT_USERID_LEN * 8;
 	entl[0] = bits_len >> 8;
 	entl[1] = bits_len & 0xff;