ksmbd: fix infinite loop in ksmbd_conn_handler_loop()

If kernel_recvmsg() return -EAGAIN in ksmbd_tcp_readv() and go round
again, It will cause infinite loop issue. And all threads from next
connections would be doing that. This patch add max retry count(2) to
avoid it. kernel_recvmsg() will wait during 7sec timeout and try to
retry two time if -EAGAIN is returned. And add flags of kvmalloc to
__GFP_NOWARN and __GFP_NORETRY to disconnect immediately without
retrying on memory alloation failure.

Fixes: 0626e664 ("cifsd: add server handler for central processing and tranport layers")
Cc: stable@vger.kernel.org
Reported-by: zdi-disclosures@trendmicro.com # ZDI-CAN-18259
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/ksmbd/connection.c

@@ -316,9 +316,12 @@ int ksmbd_conn_handler_loop(void *p)
 
 		/* 4 for rfc1002 length field */
 		size = pdu_size + 4;
-		conn->request_buf = kvmalloc(size, GFP_KERNEL);
+		conn->request_buf = kvmalloc(size,
+					     GFP_KERNEL |
+					     __GFP_NOWARN |
+					     __GFP_NORETRY);
 		if (!conn->request_buf)
-			continue;
+			break;
 
 		memcpy(conn->request_buf, hdr_buf, sizeof(hdr_buf));
 		if (!ksmbd_smb_request(conn))

fs/ksmbd/transport_tcp.c

@@ -295,6 +295,7 @@ static int ksmbd_tcp_readv(struct tcp_transport *t, struct kvec *iov_orig,
 	struct msghdr ksmbd_msg;
 	struct kvec *iov;
 	struct ksmbd_conn *conn = KSMBD_TRANS(t)->conn;
+	int max_retry = 2;
 
 	iov = get_conn_iovec(t, nr_segs);
 	if (!iov)
@@ -321,9 +322,11 @@ static int ksmbd_tcp_readv(struct tcp_transport *t, struct kvec *iov_orig,
 		} else if (conn->status == KSMBD_SESS_NEED_RECONNECT) {
 			total_read = -EAGAIN;
 			break;
-		} else if (length == -ERESTARTSYS || length == -EAGAIN) {
+		} else if ((length == -ERESTARTSYS || length == -EAGAIN) &&
+			   max_retry) {
 			usleep_range(1000, 2000);
 			length = 0;
+			max_retry--;
 			continue;
 		} else if (length <= 0) {
 			total_read = -EAGAIN;