From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Daniel Axtens <[email protected]>
Date: Thu, 21 Jan 2021 00:05:58 +1100
Subject: [PATCH] io/gzio: Add init_dynamic_block() clean up if unpacking codes
 fails

init_dynamic_block() didn't clean up gzio->tl and td in some error
paths. This left td pointing to part of tl. Then in grub_gzio_close(),
when tl was freed the storage for td would also be freed. The code then
attempts to free td explicitly, performing a UAF and then a double free.

Explicitly clean up tl and td in the error paths.

Signed-off-by: Daniel Axtens <[email protected]>
Reviewed-by: Daniel Kiper <[email protected]>
---
 grub-core/io/gzio.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/grub-core/io/gzio.c b/grub-core/io/gzio.c
index 6e9b9c936..97b34f885 100644
--- a/grub-core/io/gzio.c
+++ b/grub-core/io/gzio.c
@@ -953,7 +953,7 @@ init_dynamic_block (grub_gzio_t gzio)
 	  if ((unsigned) i + j > n)
 	    {
 	      grub_error (GRUB_ERR_BAD_COMPRESSED_DATA, "too many codes found");
-	      return;
+	      goto fail;
 	    }
 	  while (j--)
 	    ll[i++] = l;
@@ -966,7 +966,7 @@ init_dynamic_block (grub_gzio_t gzio)
 	  if ((unsigned) i + j > n)
 	    {
 	      grub_error (GRUB_ERR_BAD_COMPRESSED_DATA, "too many codes found");
-	      return;
+	      goto fail;
 	    }
 	  while (j--)
 	    ll[i++] = 0;
@@ -981,7 +981,7 @@ init_dynamic_block (grub_gzio_t gzio)
 	  if ((unsigned) i + j > n)
 	    {
 	      grub_error (GRUB_ERR_BAD_COMPRESSED_DATA, "too many codes found");
-	      return;
+	      goto fail;
 	    }
 	  while (j--)
 	    ll[i++] = 0;
@@ -1019,6 +1019,12 @@ init_dynamic_block (grub_gzio_t gzio)
   /* indicate we're now working on a block */
   gzio->code_state = 0;
   gzio->block_len++;
+  return;
+
+ fail:
+  huft_free (gzio->tl);
+  gzio->td = NULL;
+  gzio->tl = NULL;
 }