From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Daniel Axtens <dja@axtens.net>
Date: Mon, 18 Jan 2021 16:49:44 +1100
Subject: [PATCH] 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>
---
 grub-core/fs/nilfs2.c | 38 +++++++++++++++++++++++---------------
 1 file changed, 23 insertions(+), 15 deletions(-)

diff --git a/grub-core/fs/nilfs2.c b/grub-core/fs/nilfs2.c
index 61e8af9ff..054ad3dc1 100644
--- 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;