diff --git a/fs/smb/server/asn1.c b/fs/smb/server/asn1.c
index 4a4b2b03ff33..b931a99ab9c8 100644
--- a/fs/smb/server/asn1.c
+++ b/fs/smb/server/asn1.c
@@ -214,10 +214,15 @@ static int ksmbd_neg_token_alloc(void *context, size_t hdrlen,
 {
 	struct ksmbd_conn *conn = context;
 
+	if (!vlen)
+		return -EINVAL;
+
 	conn->mechToken = kmemdup_nul(value, vlen, GFP_KERNEL);
 	if (!conn->mechToken)
 		return -ENOMEM;
 
+	conn->mechTokenLen = (unsigned int)vlen;
+
 	return 0;
 }
 
diff --git a/fs/smb/server/connection.h b/fs/smb/server/connection.h
index 3c005246a32e..342f935f5770 100644
--- a/fs/smb/server/connection.h
+++ b/fs/smb/server/connection.h
@@ -88,6 +88,7 @@ struct ksmbd_conn {
 	__u16				dialect;
 
 	char				*mechToken;
+	unsigned int			mechTokenLen;
 
 	struct ksmbd_conn_ops	*conn_ops;
 
diff --git a/fs/smb/server/smb2pdu.c b/fs/smb/server/smb2pdu.c
index 0e4d514a8c2b..297ed5c5ce8d 100644
--- a/fs/smb/server/smb2pdu.c
+++ b/fs/smb/server/smb2pdu.c
@@ -1414,7 +1414,10 @@ static struct ksmbd_user *session_user(struct ksmbd_conn *conn,
 	char *name;
 	unsigned int name_off, name_len, secbuf_len;
 
-	secbuf_len = le16_to_cpu(req->SecurityBufferLength);
+	if (conn->use_spnego && conn->mechToken)
+		secbuf_len = conn->mechTokenLen;
+	else
+		secbuf_len = le16_to_cpu(req->SecurityBufferLength);
 	if (secbuf_len < sizeof(struct authenticate_message)) {
 		ksmbd_debug(SMB, "blob len %d too small\n", secbuf_len);
 		return NULL;
@@ -1505,7 +1508,10 @@ static int ntlm_authenticate(struct ksmbd_work *work,
 		struct authenticate_message *authblob;
 
 		authblob = user_authblob(conn, req);
-		sz = le16_to_cpu(req->SecurityBufferLength);
+		if (conn->use_spnego && conn->mechToken)
+			sz = conn->mechTokenLen;
+		else
+			sz = le16_to_cpu(req->SecurityBufferLength);
 		rc = ksmbd_decode_ntlmssp_auth_blob(authblob, sz, conn, sess);
 		if (rc) {
 			set_user_flag(sess->user, KSMBD_USER_FLAG_BAD_PASSWORD);
@@ -1778,8 +1784,7 @@ int smb2_sess_setup(struct ksmbd_work *work)
 
 	negblob_off = le16_to_cpu(req->SecurityBufferOffset);
 	negblob_len = le16_to_cpu(req->SecurityBufferLength);
-	if (negblob_off < offsetof(struct smb2_sess_setup_req, Buffer) ||
-	    negblob_len < offsetof(struct negotiate_message, NegotiateFlags)) {
+	if (negblob_off < offsetof(struct smb2_sess_setup_req, Buffer)) {
 		rc = -EINVAL;
 		goto out_err;
 	}
@@ -1788,8 +1793,15 @@ int smb2_sess_setup(struct ksmbd_work *work)
 			negblob_off);
 
 	if (decode_negotiation_token(conn, negblob, negblob_len) == 0) {
-		if (conn->mechToken)
+		if (conn->mechToken) {
 			negblob = (struct negotiate_message *)conn->mechToken;
+			negblob_len = conn->mechTokenLen;
+		}
+	}
+
+	if (negblob_len < offsetof(struct negotiate_message, NegotiateFlags)) {
+		rc = -EINVAL;
+		goto out_err;
 	}
 
 	if (server_conf.auth_mechs & conn->auth_mechs) {