From 4b1839b9d9220161a20041722458b39b269fb70d Mon Sep 17 00:00:00 2001
From: Daniel Axtens <dja@axtens.net>
Date: Wed, 13 Jan 2021 20:59:09 +1100
Subject: [PATCH] io/gzio: Bail if gzio->tl/td is NULL

This is an ugly fix that doesn't address why gzio->tl comes to be NULL.
However, it seems to be sufficient to patch up a bunch of NULL derefs.

It would be good to revisit this in future and see if we can have
a cleaner solution that addresses some of the causes of the unexpected
NULL pointers.

Reference: http://git.savannah.gnu.org/cgit/grub.git/commit/?id=3334a5e6c86f10e715cca3bf66ce0fc2f164b61b

Signed-off-by: Daniel Axtens <dja@axtens.net>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
---
 grub-core/io/gzio.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/grub-core/io/gzio.c b/grub-core/io/gzio.c
index 43d98a7..4a8eaea 100644
--- a/grub-core/io/gzio.c
+++ b/grub-core/io/gzio.c
@@ -669,6 +669,13 @@ inflate_codes_in_window (grub_gzio_t gzio)
     {
       if (! gzio->code_state)
 	{
+
+	  if (gzio->tl == NULL)
+	    {
+	      grub_error (GRUB_ERR_BAD_COMPRESSED_DATA, "NULL gzio->tl");
+	      return 1;
+	    }
+
 	  NEEDBITS ((unsigned) gzio->bl);
 	  if ((e = (t = gzio->tl + ((unsigned) b & ml))->e) > 16)
 	    do
@@ -707,6 +714,12 @@ inflate_codes_in_window (grub_gzio_t gzio)
 	      n = t->v.n + ((unsigned) b & mask_bits[e]);
 	      DUMPBITS (e);
 
+	      if (gzio->td == NULL)
+		{
+		  grub_error (GRUB_ERR_BAD_COMPRESSED_DATA, "NULL gzio->td");
+		  return 1;
+		}
+
 	      /* decode distance of block to copy */
 	      NEEDBITS ((unsigned) gzio->bd);
 	      if ((e = (t = gzio->td + ((unsigned) b & md))->e) > 16)
@@ -917,6 +930,13 @@ init_dynamic_block (grub_gzio_t gzio)
   n = nl + nd;
   m = mask_bits[gzio->bl];
   i = l = 0;
+
+  if (gzio->tl == NULL)
+    {
+      grub_error (GRUB_ERR_BAD_COMPRESSED_DATA, "NULL gzio->tl");
+      return;
+    }
+
   while ((unsigned) i < n)
     {
       NEEDBITS ((unsigned) gzio->bl);
-- 
2.19.1

