From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001

From: Peter Jones <pjones@redhat.com>

Date: Sun, 19 Jul 2020 16:53:27 -0400

Subject: [PATCH] efi: fix some malformed device path arithmetic errors.

Several places we take the length of a device path and subtract 4 from

it, without ever checking that it's >= 4.  There are also cases where

this kind of malformation will result in unpredictable iteration,

including treating the length from one dp node as the type in the next

node.  These are all errors, no matter where the data comes from.

This patch adds a checking macro, GRUB_EFI_DEVICE_PATH_VALID(), which

can be used in several places, and makes GRUB_EFI_NEXT_DEVICE_PATH()

return NULL and GRUB_EFI_END_ENTIRE_DEVICE_PATH() evaluate as true when

the length is too small.  Additionally, it makes several places in the

code check for and return errors in these cases.

Signed-off-by: Peter Jones <pjones@redhat.com>

Upstream-commit-id: 23e68a83990

---

 grub-core/kern/efi/efi.c           | 67 ++++++++++++++++++++++++++++++++------

 grub-core/loader/efi/chainloader.c | 19 +++++++++--

 grub-core/loader/i386/xnu.c        |  9 ++---

 include/grub/efi/api.h             | 14 +++++---

 4 files changed, 88 insertions(+), 21 deletions(-)

diff --git a/grub-core/kern/efi/efi.c b/grub-core/kern/efi/efi.c

index 4bd7ca210ad..42c68307f3f 100644

--- a/grub-core/kern/efi/efi.c

+++ b/grub-core/kern/efi/efi.c

@@ -325,7 +325,7 @@ grub_efi_get_filename (grub_efi_device_path_t *dp0)

   dp = dp0;

-  while (1)

+  while (dp)

     {

       grub_efi_uint8_t type = GRUB_EFI_DEVICE_PATH_TYPE (dp);

       grub_efi_uint8_t subtype = GRUB_EFI_DEVICE_PATH_SUBTYPE (dp);

@@ -335,9 +335,15 @@ grub_efi_get_filename (grub_efi_device_path_t *dp0)

       if (type == GRUB_EFI_MEDIA_DEVICE_PATH_TYPE

 	       && subtype == GRUB_EFI_FILE_PATH_DEVICE_PATH_SUBTYPE)

 	{

-	  grub_efi_uint16_t len;

-	  len = ((GRUB_EFI_DEVICE_PATH_LENGTH (dp) - 4)

-		 / sizeof (grub_efi_char16_t));

+	  grub_efi_uint16_t len = GRUB_EFI_DEVICE_PATH_LENGTH (dp);

+

+	  if (len < 4)

+	    {

+	      grub_error (GRUB_ERR_OUT_OF_RANGE,

+			  "malformed EFI Device Path node has length=%d", len);

+	      return NULL;

+	    }

+	  len = (len - 4) / sizeof (grub_efi_char16_t);

 	  filesize += GRUB_MAX_UTF8_PER_UTF16 * len + 2;

 	}

@@ -353,7 +359,7 @@ grub_efi_get_filename (grub_efi_device_path_t *dp0)

   if (!name)

     return NULL;

-  while (1)

+  while (dp)

     {

       grub_efi_uint8_t type = GRUB_EFI_DEVICE_PATH_TYPE (dp);

       grub_efi_uint8_t subtype = GRUB_EFI_DEVICE_PATH_SUBTYPE (dp);

@@ -369,8 +375,15 @@ grub_efi_get_filename (grub_efi_device_path_t *dp0)

 	  *p++ = '/';

-	  len = ((GRUB_EFI_DEVICE_PATH_LENGTH (dp) - 4)

-		 / sizeof (grub_efi_char16_t));

+	  len = GRUB_EFI_DEVICE_PATH_LENGTH (dp);

+	  if (len < 4)

+	    {

+	      grub_error (GRUB_ERR_OUT_OF_RANGE,

+			  "malformed EFI Device Path node has length=%d", len);

+	      return NULL;

+	    }

+

+	  len = (len - 4) / sizeof (grub_efi_char16_t);

 	  fp = (grub_efi_file_path_device_path_t *) dp;

 	  dup_name = grub_calloc (len, sizeof (*dup_name));

@@ -442,7 +455,26 @@ grub_efi_duplicate_device_path (const grub_efi_device_path_t *dp)

        ;

        p = GRUB_EFI_NEXT_DEVICE_PATH (p))

     {

-      total_size += GRUB_EFI_DEVICE_PATH_LENGTH (p);

+      grub_size_t len = GRUB_EFI_DEVICE_PATH_LENGTH (p);

+

+      /*

+       * In the event that we find a node that's completely garbage, for

+       * example if we get to 0x7f 0x01 0x02 0x00 ... (EndInstance with a size

+       * of 2), GRUB_EFI_END_ENTIRE_DEVICE_PATH() will be true and

+       * GRUB_EFI_NEXT_DEVICE_PATH() will return NULL, so we won't continue,

+       * and neither should our consumers, but there won't be any error raised

+       * even though the device path is junk.

+       *

+       * This keeps us from passing junk down back to our caller.

+       */

+      if (len < 4)

+	{

+	  grub_error (GRUB_ERR_OUT_OF_RANGE,

+		      "malformed EFI Device Path node has length=%d", len);

+	  return NULL;

+	}

+

+      total_size += len;

       if (GRUB_EFI_END_ENTIRE_DEVICE_PATH (p))

 	break;

     }

@@ -487,7 +519,7 @@ dump_vendor_path (const char *type, grub_efi_vendor_device_path_t *vendor)

 void

 grub_efi_print_device_path (grub_efi_device_path_t *dp)

 {

-  while (1)

+  while (GRUB_EFI_DEVICE_PATH_VALID (dp))

     {

       grub_efi_uint8_t type = GRUB_EFI_DEVICE_PATH_TYPE (dp);

       grub_efi_uint8_t subtype = GRUB_EFI_DEVICE_PATH_SUBTYPE (dp);

@@ -959,7 +991,11 @@ grub_efi_compare_device_paths (const grub_efi_device_path_t *dp1,

     /* Return non-zero.  */

     return 1;

-  while (1)

+  if (dp1 == dp2)

+    return 0;

+

+  while (GRUB_EFI_DEVICE_PATH_VALID (dp1)

+	 && GRUB_EFI_DEVICE_PATH_VALID (dp2))

     {

       grub_efi_uint8_t type1, type2;

       grub_efi_uint8_t subtype1, subtype2;

@@ -995,5 +1031,16 @@ grub_efi_compare_device_paths (const grub_efi_device_path_t *dp1,

       dp2 = (grub_efi_device_path_t *) ((char *) dp2 + len2);

     }

+  /*

+   * There's no "right" answer here, but we probably don't want to call a valid

+   * dp and an invalid dp equal, so pick one way or the other.

+   */

+  if (GRUB_EFI_DEVICE_PATH_VALID (dp1) &&

+      !GRUB_EFI_DEVICE_PATH_VALID (dp2))

+    return 1;

+  else if (!GRUB_EFI_DEVICE_PATH_VALID (dp1) &&

+	   GRUB_EFI_DEVICE_PATH_VALID (dp2))

+    return -1;

+

   return 0;

 }

diff --git a/grub-core/loader/efi/chainloader.c b/grub-core/loader/efi/chainloader.c

index 3d600fa6bd5..b90dfd6c5a6 100644

--- a/grub-core/loader/efi/chainloader.c

+++ b/grub-core/loader/efi/chainloader.c

@@ -125,6 +125,12 @@ copy_file_path (grub_efi_file_path_device_path_t *fp,

   fp->header.type = GRUB_EFI_MEDIA_DEVICE_PATH_TYPE;

   fp->header.subtype = GRUB_EFI_FILE_PATH_DEVICE_PATH_SUBTYPE;

+  if (!GRUB_EFI_DEVICE_PATH_VALID ((grub_efi_device_path_t *)fp))

+    {

+      grub_error (GRUB_ERR_BAD_ARGUMENT, "EFI Device Path is invalid");

+      return;

+    }

+

   path_name = grub_calloc (len, GRUB_MAX_UTF16_PER_UTF8 * sizeof (*path_name));

   if (!path_name)

     return;

@@ -164,9 +170,18 @@ make_file_path (grub_efi_device_path_t *dp, const char *filename)

   size = 0;

   d = dp;

-  while (1)

+  while (d)

     {

-      size += GRUB_EFI_DEVICE_PATH_LENGTH (d);

+      grub_size_t len = GRUB_EFI_DEVICE_PATH_LENGTH (d);

+

+      if (len < 4)

+	{

+	  grub_error (GRUB_ERR_OUT_OF_RANGE,

+		      "malformed EFI Device Path node has length=%d", len);

+	  return NULL;

+	}

+

+      size += len;

       if ((GRUB_EFI_END_ENTIRE_DEVICE_PATH (d)))

 	break;

       d = GRUB_EFI_NEXT_DEVICE_PATH (d);

diff --git a/grub-core/loader/i386/xnu.c b/grub-core/loader/i386/xnu.c

index 424488a9f7c..8a68e49ad76 100644

--- a/grub-core/loader/i386/xnu.c

+++ b/grub-core/loader/i386/xnu.c

@@ -512,14 +512,15 @@ grub_cmd_devprop_load (grub_command_t cmd __attribute__ ((unused)),

       devhead = buf;

       buf = devhead + 1;

-      dpstart = buf;

+      dp = dpstart = buf;

-      do

+      while (GRUB_EFI_DEVICE_PATH_VALID (dp) && buf < bufend)

 	{

-	  dp = buf;

 	  buf = (char *) buf + GRUB_EFI_DEVICE_PATH_LENGTH (dp);

+	  if (GRUB_EFI_END_ENTIRE_DEVICE_PATH (dp))

+	    break;

+	  dp = buf;

 	}

-      while (!GRUB_EFI_END_ENTIRE_DEVICE_PATH (dp) && buf < bufend);

       dev = grub_xnu_devprop_add_device (dpstart, (char *) buf

 					 - (char *) dpstart);

diff --git a/include/grub/efi/api.h b/include/grub/efi/api.h

index fbd1c4b529d..9860fd16189 100644

--- a/include/grub/efi/api.h

+++ b/include/grub/efi/api.h

@@ -613,6 +613,7 @@ typedef struct grub_efi_device_path grub_efi_device_path_protocol_t;

 #define GRUB_EFI_DEVICE_PATH_TYPE(dp)		((dp)->type & 0x7f)

 #define GRUB_EFI_DEVICE_PATH_SUBTYPE(dp)	((dp)->subtype)

 #define GRUB_EFI_DEVICE_PATH_LENGTH(dp)		((dp)->length)

+#define GRUB_EFI_DEVICE_PATH_VALID(dp)		((dp) != NULL && GRUB_EFI_DEVICE_PATH_LENGTH (dp) >= 4)

 /* The End of Device Path nodes.  */

 #define GRUB_EFI_END_DEVICE_PATH_TYPE			(0xff & 0x7f)

@@ -621,13 +622,16 @@ typedef struct grub_efi_device_path grub_efi_device_path_protocol_t;

 #define GRUB_EFI_END_THIS_DEVICE_PATH_SUBTYPE		0x01

 #define GRUB_EFI_END_ENTIRE_DEVICE_PATH(dp)	\

-  (GRUB_EFI_DEVICE_PATH_TYPE (dp) == GRUB_EFI_END_DEVICE_PATH_TYPE \

-   && (GRUB_EFI_DEVICE_PATH_SUBTYPE (dp) \

-       == GRUB_EFI_END_ENTIRE_DEVICE_PATH_SUBTYPE))

+  (!GRUB_EFI_DEVICE_PATH_VALID (dp) || \

+   (GRUB_EFI_DEVICE_PATH_TYPE (dp) == GRUB_EFI_END_DEVICE_PATH_TYPE \

+    && (GRUB_EFI_DEVICE_PATH_SUBTYPE (dp) \

+	== GRUB_EFI_END_ENTIRE_DEVICE_PATH_SUBTYPE)))

 #define GRUB_EFI_NEXT_DEVICE_PATH(dp)	\

-  ((grub_efi_device_path_t *) ((char *) (dp) \

-                               + GRUB_EFI_DEVICE_PATH_LENGTH (dp)))

+  (GRUB_EFI_DEVICE_PATH_VALID (dp) \

+   ? ((grub_efi_device_path_t *) \

+      ((char *) (dp) + GRUB_EFI_DEVICE_PATH_LENGTH (dp))) \

+   : NULL)

 /* Hardware Device Path.  */

 #define GRUB_EFI_HARDWARE_DEVICE_PATH_TYPE		1