ksmbd: fix deadlock in ksmbd_find_crypto_ctx()

Deadlock is triggered by sending multiple concurrent session setup
requests. It should be reused after releasing when getting ctx for crypto.
Multiple consecutive ctx uses cause deadlock while waiting for releasing
due to the limited number of ctx.

Cc: stable@vger.kernel.org
Reported-by: zdi-disclosures@trendmicro.com # ZDI-CAN-20591
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

Author: namjaejeon

fs/ksmbd/auth.c

@@ -221,22 +221,22 @@ int ksmbd_auth_ntlmv2(struct ksmbd_conn *conn, struct ksmbd_session *sess,
 {
 	char ntlmv2_hash[CIFS_ENCPWD_SIZE];
 	char ntlmv2_rsp[CIFS_HMAC_MD5_HASH_SIZE];
-	struct ksmbd_crypto_ctx *ctx;
+	struct ksmbd_crypto_ctx *ctx = NULL;
 	char *construct = NULL;
 	int rc, len;
 
-	ctx = ksmbd_crypto_ctx_find_hmacmd5();
-	if (!ctx) {
-		ksmbd_debug(AUTH, "could not crypto alloc hmacmd5\n");
-		return -ENOMEM;
-	}
-
 	rc = calc_ntlmv2_hash(conn, sess, ntlmv2_hash, domain_name);
 	if (rc) {
 		ksmbd_debug(AUTH, "could not get v2 hash rc %d\n", rc);
 		goto out;
 	}
 
+	ctx = ksmbd_crypto_ctx_find_hmacmd5();
+	if (!ctx) {
+		ksmbd_debug(AUTH, "could not crypto alloc hmacmd5\n");
+		return -ENOMEM;
+	}
+
 	rc = crypto_shash_setkey(CRYPTO_HMACMD5_TFM(ctx),
 				 ntlmv2_hash,
 				 CIFS_HMAC_MD5_HASH_SIZE);
@@ -272,6 +272,8 @@ int ksmbd_auth_ntlmv2(struct ksmbd_conn *conn, struct ksmbd_session *sess,
 		ksmbd_debug(AUTH, "Could not generate md5 hash\n");
 		goto out;
 	}
+	ksmbd_release_crypto_ctx(ctx);
+	ctx = NULL;
 
 	rc = ksmbd_gen_sess_key(sess, ntlmv2_hash, ntlmv2_rsp);
 	if (rc) {
@@ -282,7 +284,8 @@ int ksmbd_auth_ntlmv2(struct ksmbd_conn *conn, struct ksmbd_session *sess,
 	if (memcmp(ntlmv2->ntlmv2_hash, ntlmv2_rsp, CIFS_HMAC_MD5_HASH_SIZE) != 0)
 		rc = -EINVAL;
 out:
-	ksmbd_release_crypto_ctx(ctx);
+	if (ctx)
+		ksmbd_release_crypto_ctx(ctx);
 	kfree(construct);
 	return rc;
 }