[PATCH 4.9 15/32] reiserfs: add check for an invalid ih_entry_count

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Rustam Kovhaev <rkovhaev@gmail.com>

commit d24396c5290ba8ab04ba505176874c4e04a2d53c upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 fs/reiserfs/stree.c |    6 ++++++
 1 file changed, 6 insertions(+)

--- a/fs/reiserfs/stree.c
+++ b/fs/reiserfs/stree.c
@@ -453,6 +453,12 @@ static int is_leaf(char *buf, int blocks
 					 "(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);
 	}