From 2f4430cc0a44fd8c8aa7aee5c51887667ad3d6c3 Mon Sep 17 00:00:00 2001

From: Darren Kenny <darren.kenny@oracle.com>

Date: Thu, 7 Apr 2022 15:18:12 +0000

Subject: [PATCH 5/5] fs/btrfs: Fix more fuzz issues related to chunks

The corpus was generating issues in grub_btrfs_read_logical() when

attempting to iterate over stripe entries in the superblock's

bootmapping.

In most cases the reason for the failure was that the number of stripes

in chunk->nstripes exceeded the possible space statically allocated in

superblock bootmapping space. Each stripe entry in the bootmapping block

consists of a grub_btrfs_key followed by a grub_btrfs_chunk_stripe.

Another issue that came up was that while calculating the chunk size,

in an earlier piece of code in that function, depending on the data

provided in the btrfs file system, it would end up calculating a size

that was too small to contain even 1 grub_btrfs_chunk_item, which is

obviously invalid too.

Signed-off-by: Darren Kenny <darren.kenny@oracle.com>

Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

---

 grub-core/fs/btrfs.c | 24 ++++++++++++++++++++++++

 1 file changed, 24 insertions(+)

diff --git a/grub-core/fs/btrfs.c b/grub-core/fs/btrfs.c

index 73b230632..ec72f7be3 100644

--- a/grub-core/fs/btrfs.c

+++ b/grub-core/fs/btrfs.c

@@ -918,6 +918,17 @@ grub_btrfs_read_logical (struct grub_btrfs_data *data, grub_disk_addr_t addr,

 	  return grub_error (GRUB_ERR_BAD_FS,

 			     "got an invalid zero-size chunk");

 	}

+

+      /*

+       * The space being allocated for a chunk should at least be able to

+       * contain one chunk item.

+       */

+      if (chsize < sizeof (struct grub_btrfs_chunk_item))

+       {

+         grub_dprintf ("btrfs", "chunk-size too small\n");

+         return grub_error (GRUB_ERR_BAD_FS,

+                            "got an invalid chunk size");

+       }

       chunk = grub_malloc (chsize);

       if (!chunk)

 	return grub_errno;

@@ -1165,6 +1176,13 @@ grub_btrfs_read_logical (struct grub_btrfs_data *data, grub_disk_addr_t addr,

 	if (csize > (grub_uint64_t) size)

 	  csize = size;

+	/*

+	 * The space for a chunk stripe is limited to the space provide in the super-block's

+	 * bootstrap mapping with an initial btrfs key at the start of each chunk.

+	 */

+	grub_size_t avail_stripes = sizeof (data->sblock.bootstrap_mapping) /

+	  (sizeof (struct grub_btrfs_key) + sizeof (struct grub_btrfs_chunk_stripe));

+

 	for (j = 0; j < 2; j++)

 	  {

 	    grub_size_t est_chunk_alloc = 0;

@@ -1191,6 +1209,12 @@ grub_btrfs_read_logical (struct grub_btrfs_data *data, grub_disk_addr_t addr,

 		break;

 	      }

+	   if (grub_le_to_cpu16 (chunk->nstripes) > avail_stripes)

+             {

+               err = GRUB_ERR_BAD_FS;

+               break;

+             }

+

 	    if (is_raid56)

 	      {

 		err = btrfs_read_from_chunk (data, chunk, stripen,

-- 

2.33.5