File 0004-tftp-Fix-hang-when-file-is-a-directory.patch of Package grub2

From 9f8f5e0d45165b99d0f3ce9bf37382738e0bddb7 Mon Sep 17 00:00:00 2001
From: Michael Chang <mchang@suse.com>
Date: Thu, 17 Jul 2025 13:29:48 +0800
Subject: [PATCH 4/4] tftp: Fix hang when file is a directory

We observed an issue when accessing a remote directory via TFTP: GRUB
hangs indefinitely instead of returning an error immediately.

The packet capture [1] shows that the server doesn't send an error
packet right after the RRQ. Instead, it first replies with an OACK
indicating tsize=22, as if the target were a regular file. After GRUB
sends its ACK, the server then sends an error "Is a directory". GRUB
ignores this delayed error and hangs while waiting for data that never
arrives.

This happens because GRUB currently assumes any error must follow the
RRQ immediately, before data transfer begins. Once it receives an OACK,
it switches to expecting data packets and neglects any error that
arrives afterward.

To work around this, we detect an error on block 0 immediately after
OACK, set the eof and stall flags to break out of the receive loop, and
close the socket (so that tftp_close() won't send another error). GRUB
will then report the error and exit properly.

[1]
Source          Destination     Info
192.168.100.122	192.168.100.2	Read Request, File: /grub/i386-pc, Transfer type: octet, blksize=1024, tsize=0
192.168.100.2	192.168.100.122	Option Acknowledgement, blksize=1024, tsize=22
192.168.100.122	192.168.100.2	Acknowledgement, Block: 0
192.168.100.2	192.168.100.122	Error Code, Code: Not defined, Message: Is a directory

Signed-off-by: Michael Chang <mchang@suse.com>
---
 grub-core/net/tftp.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/grub-core/net/tftp.c b/grub-core/net/tftp.c
index 409b1d09b..93452fe3b 100644
--- a/grub-core/net/tftp.c
+++ b/grub-core/net/tftp.c
@@ -250,6 +250,14 @@ tftp_receive (grub_net_udp_socket_t sock __attribute__ ((unused)),
       grub_netbuff_free (nb);
       return GRUB_ERR_NONE;
     case TFTP_ERROR:
+      if (data->have_oack == 1 && data->block == 0)
+	{
+	  file->device->net->eof = 1;
+	  file->device->net->stall = 1;
+	  /* Do not send closed error code back to server in tftp_close() */
+	  grub_net_udp_close (data->sock);
+	  data->sock = NULL;
+	}
       data->have_oack = 1;
       grub_error (GRUB_ERR_IO, "%s", tftph->u.err.errmsg);
       grub_error_save (&data->save_err);
-- 
2.50.0