Blame SOURCES/0303-efi-fix-some-malformed-device-path-arithmetic-errors.patch

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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Peter Jones <pjones@redhat.com>
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Date: Sun, 19 Jul 2020 16:53:27 -0400
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Subject: [PATCH] efi: fix some malformed device path arithmetic errors.
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Several places we take the length of a device path and subtract 4 from
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it, without ever checking that it's >= 4.  There are also cases where
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this kind of malformation will result in unpredictable iteration,
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including treating the length from one dp node as the type in the next
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node.  These are all errors, no matter where the data comes from.
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This patch adds a checking macro, GRUB_EFI_DEVICE_PATH_VALID(), which
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can be used in several places, and makes GRUB_EFI_NEXT_DEVICE_PATH()
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return NULL and GRUB_EFI_END_ENTIRE_DEVICE_PATH() evaluate as true when
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the length is too small.  Additionally, it makes several places in the
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code check for and return errors in these cases.
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Signed-off-by: Peter Jones <pjones@redhat.com>
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Upstream-commit-id: 23e68a83990
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---
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 grub-core/kern/efi/efi.c           | 67 ++++++++++++++++++++++++++++++++------
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 grub-core/loader/efi/chainloader.c | 19 +++++++++--
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 grub-core/loader/i386/xnu.c        |  9 ++---
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 include/grub/efi/api.h             | 14 +++++---
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 4 files changed, 88 insertions(+), 21 deletions(-)
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diff --git a/grub-core/kern/efi/efi.c b/grub-core/kern/efi/efi.c
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index b1379b92fb8..03de9cb14e7 100644
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--- a/grub-core/kern/efi/efi.c
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+++ b/grub-core/kern/efi/efi.c
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@@ -344,7 +344,7 @@ grub_efi_get_filename (grub_efi_device_path_t *dp0)
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   dp = dp0;
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-  while (1)
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+  while (dp)
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     {
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       grub_efi_uint8_t type = GRUB_EFI_DEVICE_PATH_TYPE (dp);
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       grub_efi_uint8_t subtype = GRUB_EFI_DEVICE_PATH_SUBTYPE (dp);
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@@ -354,9 +354,15 @@ grub_efi_get_filename (grub_efi_device_path_t *dp0)
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       if (type == GRUB_EFI_MEDIA_DEVICE_PATH_TYPE
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 	       && subtype == GRUB_EFI_FILE_PATH_DEVICE_PATH_SUBTYPE)
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 	{
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-	  grub_efi_uint16_t len;
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-	  len = ((GRUB_EFI_DEVICE_PATH_LENGTH (dp) - 4)
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-		 / sizeof (grub_efi_char16_t));
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+	  grub_efi_uint16_t len = GRUB_EFI_DEVICE_PATH_LENGTH (dp);
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+
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+	  if (len < 4)
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+	    {
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+	      grub_error (GRUB_ERR_OUT_OF_RANGE,
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+			  "malformed EFI Device Path node has length=%d", len);
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+	      return NULL;
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+	    }
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+	  len = (len - 4) / sizeof (grub_efi_char16_t);
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 	  filesize += GRUB_MAX_UTF8_PER_UTF16 * len + 2;
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 	}
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@@ -372,7 +378,7 @@ grub_efi_get_filename (grub_efi_device_path_t *dp0)
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   if (!name)
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     return NULL;
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-  while (1)
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+  while (dp)
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     {
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       grub_efi_uint8_t type = GRUB_EFI_DEVICE_PATH_TYPE (dp);
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       grub_efi_uint8_t subtype = GRUB_EFI_DEVICE_PATH_SUBTYPE (dp);
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@@ -388,8 +394,15 @@ grub_efi_get_filename (grub_efi_device_path_t *dp0)
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 	  *p++ = '/';
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-	  len = ((GRUB_EFI_DEVICE_PATH_LENGTH (dp) - 4)
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-		 / sizeof (grub_efi_char16_t));
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+	  len = GRUB_EFI_DEVICE_PATH_LENGTH (dp);
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+	  if (len < 4)
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+	    {
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+	      grub_error (GRUB_ERR_OUT_OF_RANGE,
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+			  "malformed EFI Device Path node has length=%d", len);
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+	      return NULL;
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+	    }
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+
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+	  len = (len - 4) / sizeof (grub_efi_char16_t);
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 	  fp = (grub_efi_file_path_device_path_t *) dp;
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 	  /* According to EFI spec Path Name is NULL terminated */
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 	  while (len > 0 && fp->path_name[len - 1] == 0)
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@@ -464,7 +477,26 @@ grub_efi_duplicate_device_path (const grub_efi_device_path_t *dp)
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        ;
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        p = GRUB_EFI_NEXT_DEVICE_PATH (p))
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     {
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-      total_size += GRUB_EFI_DEVICE_PATH_LENGTH (p);
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+      grub_size_t len = GRUB_EFI_DEVICE_PATH_LENGTH (p);
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+
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+      /*
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+       * In the event that we find a node that's completely garbage, for
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+       * example if we get to 0x7f 0x01 0x02 0x00 ... (EndInstance with a size
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+       * of 2), GRUB_EFI_END_ENTIRE_DEVICE_PATH() will be true and
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+       * GRUB_EFI_NEXT_DEVICE_PATH() will return NULL, so we won't continue,
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+       * and neither should our consumers, but there won't be any error raised
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+       * even though the device path is junk.
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+       *
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+       * This keeps us from passing junk down back to our caller.
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+       */
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+      if (len < 4)
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+	{
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+	  grub_error (GRUB_ERR_OUT_OF_RANGE,
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+		      "malformed EFI Device Path node has length=%d", len);
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+	  return NULL;
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+	}
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+
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+      total_size += len;
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       if (GRUB_EFI_END_ENTIRE_DEVICE_PATH (p))
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 	break;
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     }
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@@ -509,7 +541,7 @@ dump_vendor_path (const char *type, grub_efi_vendor_device_path_t *vendor)
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 void
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 grub_efi_print_device_path (grub_efi_device_path_t *dp)
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 {
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-  while (1)
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+  while (GRUB_EFI_DEVICE_PATH_VALID (dp))
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     {
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       grub_efi_uint8_t type = GRUB_EFI_DEVICE_PATH_TYPE (dp);
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       grub_efi_uint8_t subtype = GRUB_EFI_DEVICE_PATH_SUBTYPE (dp);
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@@ -981,7 +1013,11 @@ grub_efi_compare_device_paths (const grub_efi_device_path_t *dp1,
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     /* Return non-zero.  */
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     return 1;
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-  while (1)
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+  if (dp1 == dp2)
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+    return 0;
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+
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+  while (GRUB_EFI_DEVICE_PATH_VALID (dp1)
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+	 && GRUB_EFI_DEVICE_PATH_VALID (dp2))
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     {
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       grub_efi_uint8_t type1, type2;
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       grub_efi_uint8_t subtype1, subtype2;
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@@ -1017,5 +1053,16 @@ grub_efi_compare_device_paths (const grub_efi_device_path_t *dp1,
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       dp2 = (grub_efi_device_path_t *) ((char *) dp2 + len2);
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     }
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+  /*
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+   * There's no "right" answer here, but we probably don't want to call a valid
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+   * dp and an invalid dp equal, so pick one way or the other.
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+   */
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+  if (GRUB_EFI_DEVICE_PATH_VALID (dp1) &&
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+      !GRUB_EFI_DEVICE_PATH_VALID (dp2))
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+    return 1;
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+  else if (!GRUB_EFI_DEVICE_PATH_VALID (dp1) &&
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+	   GRUB_EFI_DEVICE_PATH_VALID (dp2))
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+    return -1;
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+
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   return 0;
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 }
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diff --git a/grub-core/loader/efi/chainloader.c b/grub-core/loader/efi/chainloader.c
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index 2da119ad513..c2411b6dab2 100644
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--- a/grub-core/loader/efi/chainloader.c
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+++ b/grub-core/loader/efi/chainloader.c
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@@ -125,6 +125,12 @@ copy_file_path (grub_efi_file_path_device_path_t *fp,
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   fp->header.type = GRUB_EFI_MEDIA_DEVICE_PATH_TYPE;
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   fp->header.subtype = GRUB_EFI_FILE_PATH_DEVICE_PATH_SUBTYPE;
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+  if (!GRUB_EFI_DEVICE_PATH_VALID ((grub_efi_device_path_t *)fp))
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+    {
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+      grub_error (GRUB_ERR_BAD_ARGUMENT, "EFI Device Path is invalid");
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+      return;
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+    }
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+
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   path_name = grub_calloc (len, GRUB_MAX_UTF16_PER_UTF8 * sizeof (*path_name));
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   if (!path_name)
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     return;
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@@ -164,9 +170,18 @@ make_file_path (grub_efi_device_path_t *dp, const char *filename)
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   size = 0;
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   d = dp;
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-  while (1)
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+  while (d)
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     {
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-      size += GRUB_EFI_DEVICE_PATH_LENGTH (d);
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+      grub_size_t len = GRUB_EFI_DEVICE_PATH_LENGTH (d);
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+
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+      if (len < 4)
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+	{
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+	  grub_error (GRUB_ERR_OUT_OF_RANGE,
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+		      "malformed EFI Device Path node has length=%d", len);
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+	  return NULL;
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+	}
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+
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+      size += len;
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       if ((GRUB_EFI_END_ENTIRE_DEVICE_PATH (d)))
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 	break;
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       d = GRUB_EFI_NEXT_DEVICE_PATH (d);
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diff --git a/grub-core/loader/i386/xnu.c b/grub-core/loader/i386/xnu.c
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index c760db30fc0..44f7ebfa2b6 100644
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--- a/grub-core/loader/i386/xnu.c
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+++ b/grub-core/loader/i386/xnu.c
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@@ -515,14 +515,15 @@ grub_cmd_devprop_load (grub_command_t cmd __attribute__ ((unused)),
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       devhead = buf;
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       buf = devhead + 1;
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-      dpstart = buf;
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+      dp = dpstart = buf;
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-      do
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+      while (GRUB_EFI_DEVICE_PATH_VALID (dp) && buf < bufend)
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 	{
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-	  dp = buf;
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 	  buf = (char *) buf + GRUB_EFI_DEVICE_PATH_LENGTH (dp);
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+	  if (GRUB_EFI_END_ENTIRE_DEVICE_PATH (dp))
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+	    break;
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+	  dp = buf;
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 	}
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-      while (!GRUB_EFI_END_ENTIRE_DEVICE_PATH (dp) && buf < bufend);
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       dev = grub_xnu_devprop_add_device (dpstart, (char *) buf
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 					 - (char *) dpstart);
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diff --git a/include/grub/efi/api.h b/include/grub/efi/api.h
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index 6c440c61316..a092fddb629 100644
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--- a/include/grub/efi/api.h
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+++ b/include/grub/efi/api.h
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@@ -671,6 +671,7 @@ typedef struct grub_efi_device_path grub_efi_device_path_protocol_t;
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 #define GRUB_EFI_DEVICE_PATH_TYPE(dp)		((dp)->type & 0x7f)
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 #define GRUB_EFI_DEVICE_PATH_SUBTYPE(dp)	((dp)->subtype)
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 #define GRUB_EFI_DEVICE_PATH_LENGTH(dp)		((dp)->length)
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+#define GRUB_EFI_DEVICE_PATH_VALID(dp)		((dp) != NULL && GRUB_EFI_DEVICE_PATH_LENGTH (dp) >= 4)
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 /* The End of Device Path nodes.  */
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 #define GRUB_EFI_END_DEVICE_PATH_TYPE			(0xff & 0x7f)
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@@ -679,13 +680,16 @@ typedef struct grub_efi_device_path grub_efi_device_path_protocol_t;
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 #define GRUB_EFI_END_THIS_DEVICE_PATH_SUBTYPE		0x01
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 #define GRUB_EFI_END_ENTIRE_DEVICE_PATH(dp)	\
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-  (GRUB_EFI_DEVICE_PATH_TYPE (dp) == GRUB_EFI_END_DEVICE_PATH_TYPE \
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-   && (GRUB_EFI_DEVICE_PATH_SUBTYPE (dp) \
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-       == GRUB_EFI_END_ENTIRE_DEVICE_PATH_SUBTYPE))
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+  (!GRUB_EFI_DEVICE_PATH_VALID (dp) || \
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+   (GRUB_EFI_DEVICE_PATH_TYPE (dp) == GRUB_EFI_END_DEVICE_PATH_TYPE \
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+    && (GRUB_EFI_DEVICE_PATH_SUBTYPE (dp) \
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+	== GRUB_EFI_END_ENTIRE_DEVICE_PATH_SUBTYPE)))
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 #define GRUB_EFI_NEXT_DEVICE_PATH(dp)	\
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-  ((grub_efi_device_path_t *) ((char *) (dp) \
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-                               + GRUB_EFI_DEVICE_PATH_LENGTH (dp)))
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+  (GRUB_EFI_DEVICE_PATH_VALID (dp) \
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+   ? ((grub_efi_device_path_t *) \
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+      ((char *) (dp) + GRUB_EFI_DEVICE_PATH_LENGTH (dp))) \
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+   : NULL)
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 /* Hardware Device Path.  */
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 #define GRUB_EFI_HARDWARE_DEVICE_PATH_TYPE		1