fs/nilfs2: Don't search children if provided number is too large

NILFS2 reads the number of children a node has from the node. Unfortunately,
that's not trustworthy. Check if it's beyond what the filesystem permits and
reject it if so.

This blocks some OOB reads. I'm not sure how controllable the read is and what
could be done with invalidly read data later on.

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

diff --git a/grub-core/fs/nilfs2.c b/grub-core/fs/nilfs2.c
index 20053caf5ec79f9b0c14036e9c2e4790548b8510..7963b4ef5d4de71cb43d768519f66fdc4dce3b75 100644 (file)
--- a/grub-core/fs/nilfs2.c
+++ b/grub-core/fs/nilfs2.c
@@ -416,14 +416,34 @@ grub_nilfs2_btree_node_get_key (struct grub_nilfs2_btree_node *node,
 }
 
 static inline int
-grub_nilfs2_btree_node_lookup (struct grub_nilfs2_btree_node *node,
+grub_nilfs2_btree_node_nchildren_max (struct grub_nilfs2_data *data,
+                                     struct grub_nilfs2_btree_node *node)
+{
+  int node_children_max = ((NILFS2_BLOCK_SIZE (data) -
+                           sizeof (struct grub_nilfs2_btree_node) -
+                           NILFS_BTREE_NODE_EXTRA_PAD_SIZE) /
+                          (sizeof (grub_uint64_t) + sizeof (grub_uint64_t)));
+
+  return (node->bn_flags & NILFS_BTREE_NODE_ROOT) ? 3 : node_children_max;
+}
+
+static inline int
+grub_nilfs2_btree_node_lookup (struct grub_nilfs2_data *data,
+                              struct grub_nilfs2_btree_node *node,
                               grub_uint64_t key, int *indexp)
 {
   grub_uint64_t nkey;
   int index, low, high, s;
 
   low = 0;
+
   high = grub_le_to_cpu16 (node->bn_nchildren) - 1;
+  if (high >= grub_nilfs2_btree_node_nchildren_max (data, node))
+    {
+      grub_error (GRUB_ERR_BAD_FS, "too many children");
+      return 0;
+    }
+
   index = 0;
   s = 0;
   while (low <= high)
@@ -459,18 +479,6 @@ grub_nilfs2_btree_node_lookup (struct grub_nilfs2_btree_node *node,
   return s == 0;
 }
 
-static inline int
-grub_nilfs2_btree_node_nchildren_max (struct grub_nilfs2_data *data,
-                                     struct grub_nilfs2_btree_node *node)
-{
-  int node_children_max = ((NILFS2_BLOCK_SIZE (data) -
-                           sizeof (struct grub_nilfs2_btree_node) -
-                           NILFS_BTREE_NODE_EXTRA_PAD_SIZE) /
-                          (sizeof (grub_uint64_t) + sizeof (grub_uint64_t)));
-
-  return (node->bn_flags & NILFS_BTREE_NODE_ROOT) ? 3 : node_children_max;
-}
-
 static inline grub_uint64_t *
 grub_nilfs2_btree_node_dptrs (struct grub_nilfs2_data *data,
                              struct grub_nilfs2_btree_node *node)
@@ -517,7 +525,7 @@ grub_nilfs2_btree_lookup (struct grub_nilfs2_data *data,
   node = grub_nilfs2_btree_get_root (inode);
   level = grub_nilfs2_btree_get_level (node);
 
-  found = grub_nilfs2_btree_node_lookup (node, key, &index);
+  found = grub_nilfs2_btree_node_lookup (data, node, key, &index);
   ptr = grub_nilfs2_btree_node_get_ptr (data, node, index);
   if (need_translate)
     ptr = grub_nilfs2_dat_translate (data, ptr);
@@ -538,7 +546,7 @@ grub_nilfs2_btree_lookup (struct grub_nilfs2_data *data,
        }
 
       if (!found)
-       found = grub_nilfs2_btree_node_lookup (node, key, &index);
+       found = grub_nilfs2_btree_node_lookup (data, node, key, &index);
       else
        index = 0;