fs/ext2: Fix out-of-bounds read for inline extents

When inline extents are used, i.e. the extent tree depth equals zero,
a maximum of four entries can fit into the inode's data block. If the
extent header states a number of entries greater than four the current
ext2 implementation causes an out-of-bounds read. Fix this issue by
capping the number of extents to four when reading inline extents.

Reported-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Michael Chang <mchang@suse.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

diff --git a/grub-core/fs/ext2.c b/grub-core/fs/ext2.c
index e1cc5e62aa31ddd2fab84caa078853a7e3e6201d..3f9f6b208006853038289714dfa61726ed0a5b4d 100644 (file)
--- a/grub-core/fs/ext2.c
+++ b/grub-core/fs/ext2.c
@@ -495,6 +495,8 @@ grub_ext2_read_block (grub_fshelp_node_t node, grub_disk_addr_t fileblock)
       struct grub_ext4_extent *ext;
       int i;
       grub_disk_addr_t ret;
+      grub_uint16_t nent;
+      const grub_uint16_t max_inline_ext = sizeof (inode->blocks) / sizeof (*ext) - 1; /* Minus 1 extent header. */
 
       if (grub_ext4_find_leaf (data, (struct grub_ext4_extent_header *) inode->blocks.dir_blocks,
                               fileblock, &leaf) != GRUB_ERR_NONE)
@@ -508,7 +510,13 @@ grub_ext2_read_block (grub_fshelp_node_t node, grub_disk_addr_t fileblock)
         return 0;
 
       ext = (struct grub_ext4_extent *) (leaf + 1);
-      for (i = 0; i < grub_le_to_cpu16 (leaf->entries); i++)
+
+      nent = grub_le_to_cpu16 (leaf->entries);
+
+      if (leaf->depth == 0)
+       nent = grub_min (nent, max_inline_ext);
+
+      for (i = 0; i < nent; i++)
         {
           if (fileblock < grub_le_to_cpu32 (ext[i].block))
             break;