fs/btrfs: Fix several fuzz issues with invalid dir item sizing

According to the btrfs code in Linux, the structure of a directory item
leaf should be of the form:

  |struct btrfs_dir_item|name|data|

in GRUB the name len and data len are in the grub_btrfs_dir_item
structure's n and m fields respectively.

The combined size of the structure, name and data should be less than
the allocated memory, a difference to the Linux kernel's struct
btrfs_dir_item is that the grub_btrfs_dir_item has an extra field for
where the name is stored, so we adjust for that too.

Signed-off-by: Darren Kenny <darren.kenny@oracle.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

1 files changed, 26 insertions, 0 deletions

diff --git a/grub-core/fs/btrfs.c b/grub-core/fs/btrfs.c
index 937153306..139c6616d 100644
--- a/grub-core/fs/btrfs.c
+++ b/grub-core/fs/btrfs.c
@@ -1991,6 +1991,7 @@ grub_btrfs_dir (grub_device_t device, const char *path,
   int r = 0;
   grub_uint64_t tree;
   grub_uint8_t type;
+  grub_size_t est_size = 0;
 
   if (!data)
     return grub_errno;
@@ -2049,6 +2050,18 @@ grub_btrfs_dir (grub_device_t device, const char *path,
 	  break;
 	}
 
+      if (direl == NULL ||
+	  grub_add (grub_le_to_cpu16 (direl->n),
+		    grub_le_to_cpu16 (direl->m), &est_size) ||
+	  grub_add (est_size, sizeof (*direl), &est_size) ||
+	  grub_sub (est_size, sizeof (direl->name), &est_size) ||
+	  est_size > allocated)
+       {
+         grub_errno = GRUB_ERR_OUT_OF_RANGE;
+         r = -grub_errno;
+         goto out;
+       }
+
       for (cdirel = direl;
 	   (grub_uint8_t *) cdirel - (grub_uint8_t *) direl
 	   < (grub_ssize_t) elemsize;
@@ -2059,6 +2072,19 @@ grub_btrfs_dir (grub_device_t device, const char *path,
 	  char c;
 	  struct grub_btrfs_inode inode;
 	  struct grub_dirhook_info info;
+
+	  if (cdirel == NULL ||
+	      grub_add (grub_le_to_cpu16 (cdirel->n),
+			grub_le_to_cpu16 (cdirel->m), &est_size) ||
+	      grub_add (est_size, sizeof (*cdirel), &est_size) ||
+	      grub_sub (est_size, sizeof (cdirel->name), &est_size) ||
+	      est_size > allocated)
+	   {
+	     grub_errno = GRUB_ERR_OUT_OF_RANGE;
+	     r = -grub_errno;
+	     goto out;
+	   }
+
 	  err = grub_btrfs_read_inode (data, &inode, cdirel->key.object_id,
 				       tree);
 	  grub_memset (&info, 0, sizeof (info));