[PATCH 1/2] fdtdump: add grub_fdt_prop_to_string() for safe string conversion

[Tobias Heider]

Device tree properties are not explicitly typed but values can take
multiple forms from strings to arrays and byte-strings.
grub_fdt_prop_to_string() adds a heuristic to determine the type and
convert it to a string for printing.

Signed-off-by: Tobias Heider <tobias.heider@canonical.com>
---
 grub-core/lib/fdt.c        | 87 ++++++++++++++++++++++++++++++++++++++
 grub-core/loader/efi/fdt.c | 15 +++++--
 include/grub/fdt.h         |  3 ++
 3 files changed, 101 insertions(+), 4 deletions(-)

diff --git a/grub-core/lib/fdt.c b/grub-core/lib/fdt.c
index 73cfa94a2..5ec32ac56 100644
--- a/grub-core/lib/fdt.c
+++ b/grub-core/lib/fdt.c
@@ -1,6 +1,7 @@
 /*
  *  GRUB  --  GRand Unified Bootloader
  *  Copyright (C) 2013  Free Software Foundation, Inc.
+ *  Copyright (C) 2024  Canonical, Ltd.
  *
  *  GRUB is free software: you can redistribute it and/or modify
  *  it under the terms of the GNU General Public License as published by
@@ -501,6 +502,92 @@ int grub_fdt_set_prop (void *fdt, unsigned int nodeoffset, 
const char *name,
   return 0;
 }
 
+static int
+prop_isstring (const unsigned char *str, grub_uint32_t len)
+{
+  grub_uint32_t i;
+  int is_nonzero = 0;
+
+  if (!len || str[len - 1])
+    return 0;
+
+  for (i = 0; i < len; i++)
+    {
+      if (!str[i])
+        {
+          if (!is_nonzero)
+            return 0;
+
+          is_nonzero = 0;
+          continue;
+        }
+      if (!grub_isprint (str[i]))
+        return 0;
+
+      is_nonzero = 1;
+    }
+  return 1;
+}
+
+char *
+grub_fdt_prop_to_string (const unsigned char *val, grub_uint32_t len)
+{
+  char *str;
+  int pos, slen;
+  grub_uint32_t i;
+
+  if (prop_isstring (val, len))
+    {
+      /* string */
+      return grub_strdup ((const char *)val);
+    }
+  else if (len & 0x3)
+    {
+      /* byte string */
+      grub_printf ("[");
+
+      slen = (len * 3) + 2;
+      str = grub_malloc (slen);
+      if (str == NULL)
+        return NULL;
+
+      pos = 0;
+      str[pos++] = '[';
+      for (i = 0; i < len; i++)
+        {
+          pos += grub_snprintf (&str[pos], slen - pos, "%02x", val[i]);
+          if (i != len - 1)
+            str[pos++] = ' ';
+        }
+      str[pos++] = ']';
+      str[pos] = '\0';
+    }
+  else
+    {
+      /* cell list */
+      const grub_uint32_t *cell = (const grub_uint32_t *)val;
+
+      slen = (len * 11) + 2;
+      str = grub_malloc (slen);
+      if (str == NULL)
+        return NULL;
+
+      pos = 0;
+      str[pos++] = '<';
+      for (i = 0, len /= 4; i < len; i++)
+        {
+          pos += grub_snprintf (&str[pos], slen - pos, "0x%08x",
+                                grub_be_to_cpu32 (cell[i]));
+          if (i != len - 1)
+            str[pos++] = ' ';
+        }
+      str[pos++] = '>';
+      str[pos] = '\0';
+    }
+
+  return str;
+}
+
 int
 grub_fdt_create_empty_tree (void *fdt, unsigned int size)
 {
diff --git a/grub-core/loader/efi/fdt.c b/grub-core/loader/efi/fdt.c
index e510b3491..b43ff730d 100644
--- a/grub-core/loader/efi/fdt.c
+++ b/grub-core/loader/efi/fdt.c
@@ -183,8 +183,10 @@ grub_cmd_fdtdump (grub_extcmd_context_t ctxt,
                  char **argv __attribute__ ((unused)))
 {
   struct grub_arg_list *state = ctxt->state;
-  const char *value = NULL;
+  const unsigned char *value = NULL;
+  char *str;
   void *fw_fdt;
+  grub_uint32_t len;
 
   fw_fdt = grub_efi_get_firmware_fdt ();
   if (fw_fdt == NULL)
@@ -192,17 +194,22 @@ grub_cmd_fdtdump (grub_extcmd_context_t ctxt,
                          N_("No device tree found"));
 
   if (state[0].set)
-      value = grub_fdt_get_prop (fw_fdt, 0, state[0].arg, NULL);
+      value = grub_fdt_get_prop (fw_fdt, 0, state[0].arg, &len);
 
   if (value == NULL)
     return grub_error (GRUB_ERR_OUT_OF_RANGE,
                        N_("failed to retrieve the prop field"));
 
+  str = grub_fdt_prop_to_string (value, len);
+  if (str == NULL)
+    return grub_error (GRUB_ERR_IO, N_("Failed to print string"));
+
   if (state[1].set)
-    grub_env_set (state[1].arg, value);
+    grub_env_set (state[1].arg, str);
   else
-    grub_printf ("%s\n", value);
+    grub_printf ("%s", str);
 
+  grub_free (str);
   return GRUB_ERR_NONE;
 }
 
diff --git a/include/grub/fdt.h b/include/grub/fdt.h
index e609c7e41..4db644544 100644
--- a/include/grub/fdt.h
+++ b/include/grub/fdt.h
@@ -118,6 +118,9 @@ EXPORT_FUNC(grub_fdt_get_nodename) (const void *fdt, 
unsigned int nodeoffset);
 const void *EXPORT_FUNC(grub_fdt_get_prop) (const void *fdt, unsigned int 
nodeoffset, const char *name,
                                            grub_uint32_t *len);
 
+char *EXPORT_FUNC(grub_fdt_prop_to_string) (const unsigned char *val,
+                                            grub_uint32_t len);
+
 int EXPORT_FUNC(grub_fdt_set_prop) (void *fdt, unsigned int nodeoffset, const 
char *name,
                                    const void *val, grub_uint32_t len);
 #define grub_fdt_set_prop32(fdt, nodeoffset, name, val)        \
-- 
2.43.0