reiserfs: add check for an invalid ih_entry_count

when directory item has an invalid value set for ih_entry_count it might
trigger use-after-free or out-of-bounds read in bin_search_in_dir_item()

ih_entry_count * IH_SIZE for directory item should not be larger than
ih_item_len

Link: https://lore.kernel.org/r/20201101140958.3650143-1-rkovhaev@gmail.com
Reported-and-tested-by: syzbot+83b6f7cf9922cae5c4d7@syzkaller.appspotmail.com
Link: https://syzkaller.appspot.com/bug?extid=83b6f7cf9922cae5c4d7
Signed-off-by: Rustam Kovhaev <rkovhaev@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>

diff --git a/fs/reiserfs/stree.c b/fs/reiserfs/stree.c
index 8bf88d6..476a7ff 100644 (file)
--- a/fs/reiserfs/stree.c
+++ b/fs/reiserfs/stree.c
@@ -454,6 +454,12 @@ static int is_leaf(char *buf, int blocksize, struct buffer_head *bh)
                                         "(second one): %h", ih);
                        return 0;
                }
+               if (is_direntry_le_ih(ih) && (ih_item_len(ih) < (ih_entry_count(ih) * IH_SIZE))) {
+                       reiserfs_warning(NULL, "reiserfs-5093",
+                                        "item entry count seems wrong %h",
+                                        ih);
+                       return 0;
+               }
                prev_location = ih_location(ih);
        }