From 7317421fa3343bc1aaf2a631a26b17a3a7bff9a7 Mon Sep 17 00:00:00 2001
From: Darren Kenny <darren.kenny@oracle.com>
Date: Fri, 4 Dec 2020 15:39:00 +0000
Subject: [PATCH] video/readers/jpeg: Test for an invalid next marker reference
 from a jpeg file

While it may never happen, and potentially could be caught at the end of
the function, it is worth checking up front for a bad reference to the
next marker just in case of a maliciously crafted file being provided.

Fixes: CID 73694

Reference: http://git.savannah.gnu.org/cgit/grub.git/commit/?id=5f5eb7ca8e971227e95745abe541df3e1509360e

Signed-off-by: Darren Kenny <darren.kenny@oracle.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
---
 grub-core/video/readers/jpeg.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/grub-core/video/readers/jpeg.c b/grub-core/video/readers/jpeg.c
index 31359a4..0b6ce3c 100644
--- a/grub-core/video/readers/jpeg.c
+++ b/grub-core/video/readers/jpeg.c
@@ -253,6 +253,12 @@ grub_jpeg_decode_quan_table (struct grub_jpeg_data *data)
   next_marker = data->file->offset;
   next_marker += grub_jpeg_get_word (data);
 
+  if (next_marker > data->file->size)
+    {
+      /* Should never be set beyond the size of the file. */
+      return grub_error (GRUB_ERR_BAD_FILE_TYPE, "jpeg: invalid next reference");
+    }
+
   while (data->file->offset + sizeof (data->quan_table[id]) + 1
 	 <= next_marker)
     {
-- 
2.19.1