From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Javier Martinez Canillas <javierm@redhat.com>
Date: Thu, 8 Jul 2021 16:39:39 +0200
Subject: [PATCH] normal/main: Discover the device to read the config from as a
 fallback

The GRUB core.img is generated locally, when this is done the grub2-probe
tool figures out the device and partition that needs to be read to parse
the GRUB configuration file.

But in some cases the core.img can't be generated on the host and instead
has to be done at package build time. For example, if needs to get signed
with a key that's only available on the package building infrastructure.

If that's the case, the prefix variable won't have a device and partition
but only a directory path. So there's no way for GRUB to know from which
device has to read the configuration file.

To allow GRUB to continue working on that scenario, fallback to iterating
over all the available devices, if reading the config failed when using
the prefix and fw_path variables.

Related: rhbz#1899864

Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
---
 grub-core/normal/main.c | 58 +++++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 51 insertions(+), 7 deletions(-)

diff --git a/grub-core/normal/main.c b/grub-core/normal/main.c
index 49141039f8f..93f33c16732 100644
--- a/grub-core/normal/main.c
+++ b/grub-core/normal/main.c
@@ -333,16 +333,11 @@ grub_enter_normal_mode (const char *config)
 }
 
 static grub_err_t
-grub_try_normal (const char *variable)
+grub_try_normal_prefix (const char *prefix)
 {
     char *config;
-    const char *prefix;
     grub_err_t err = GRUB_ERR_FILE_NOT_FOUND;
 
-    prefix = grub_env_get (variable);
-    if (!prefix)
-      return GRUB_ERR_FILE_NOT_FOUND;
-
     if (grub_strncmp (prefix + 1, "tftp", sizeof ("tftp") - 1) == 0)
       {
 	grub_size_t config_len;
@@ -351,7 +346,7 @@ grub_try_normal (const char *variable)
 	config = grub_malloc (config_len);
 
 	if (! config)
-	  return GRUB_ERR_FILE_NOT_FOUND;
+	  return err;
 
 	grub_snprintf (config, config_len, "%s/grub.cfg", prefix);
 	err = grub_net_search_configfile (config);
@@ -380,6 +375,53 @@ grub_try_normal (const char *variable)
     return err;
 }
 
+static int
+grub_try_normal_dev (const char *name, void *data)
+{
+  grub_err_t err;
+  const char *prefix = grub_xasprintf ("(%s)%s", name, (char *)data);
+
+  if (!prefix)
+    return 0;
+
+  err = grub_try_normal_prefix (prefix);
+  if (err == GRUB_ERR_NONE)
+    return 1;
+
+  return 0;
+}
+
+static grub_err_t
+grub_try_normal_discover (void)
+{
+  char *prefix = grub_env_get ("prefix");
+  grub_err_t err = GRUB_ERR_FILE_NOT_FOUND;
+
+  if (!prefix)
+    return err;
+
+  if (grub_device_iterate (grub_try_normal_dev, (void *)prefix))
+    return GRUB_ERR_NONE;
+
+  return err;
+}
+
+static grub_err_t
+grub_try_normal (const char *variable)
+{
+  grub_err_t err = GRUB_ERR_FILE_NOT_FOUND;
+  const char *prefix;
+
+  if (!variable)
+    return err;
+
+  prefix = grub_env_get (variable);
+  if (!prefix)
+    return err;
+
+  return grub_try_normal_prefix (prefix);
+}
+
 /* Enter normal mode from rescue mode.  */
 static grub_err_t
 grub_cmd_normal (struct grub_command *cmd __attribute__ ((unused)),
@@ -394,6 +436,8 @@ grub_cmd_normal (struct grub_command *cmd __attribute__ ((unused)),
       err = grub_try_normal ("fw_path");
       if (err == GRUB_ERR_FILE_NOT_FOUND)
         err = grub_try_normal ("prefix");
+      if (err == GRUB_ERR_FILE_NOT_FOUND)
+        err = grub_try_normal_discover ();
       if (err == GRUB_ERR_FILE_NOT_FOUND)
         grub_enter_normal_mode (0);
     }