[PATCH v2 1/3] ntfs: do not read an index block outside $INDEX_ALLOCATION

[Wahid Khan]

A directory whose $INDEX_ROOT has a child node but whose
$INDEX_ALLOCATION is missing or damaged gets an empty index inode from
ntfs_read_locked_index_inode(): size 0 and not non-resident.
ntfs_lookup_inode_by_name() still follows the child node and reads a
folio from that inode while it holds the mft record lock of the
directory.

Since the resident iomap read started to take base_ni->mrec_lock, that
read waits for a lock the caller already holds:

  INFO: task init:1 is blocked on a mutex likely owned by task init:1.
   __mutex_lock
   __ntfs_read_iomap_begin
   ntfs_read_iomap_next
   iomap_read_folio
   ntfs_read_folio
   ntfs_lookup_inode_by_name
   ntfs_lookup

The task never returns, and neither does anything else that needs the
directory's mft record.

It takes one corrupted byte on an image from mkntfs: change the first
byte of the type of the $INDEX_ALLOCATION attribute header of a
directory with index blocks from 0xa0 to 0x00. The first lookup in that
directory hangs.

Check that the index inode is non-resident and that the vcn lies inside
it before every index block read, and fail with -EIO otherwise. This
also rejects a negative vcn, which was only checked on later descents.

Fixes: d9e00c457d4a ("ntfs: serialize resident iomap reads with mrec_lock")
Cc: stable@xxxxxxxxxxxxxxx # v7.3+
Signed-off-by: Wahid Khan <wahidzk0091@xxxxxxxxx>
---
 fs/ntfs/dir.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/fs/ntfs/dir.c b/fs/ntfs/dir.c
index fce10baa2..9fb5bb3d3 100644
--- a/fs/ntfs/dir.c
+++ b/fs/ntfs/dir.c
@@ -308,6 +308,20 @@ u64 ntfs_lookup_inode_by_name(struct ntfs_inode *dir_ni, const __le16 *uname,
 
 	ia_mapping = ia_vi->i_mapping;
 descend_into_child_node:
+	/*
+	 * The child node has to be inside $INDEX_ALLOCATION. A directory that
+	 * lacks the attribute gets an empty index inode that is not
+	 * non-resident, and reading a folio from it locks the mft record that
+	 * is already locked here.
+	 */
+	if (!NInoNonResident(NTFS_I(ia_vi)) || vcn < 0 ||
+	    (u64)vcn >= (u64)i_size_read(ia_vi) >> dir_ni->itype.index.vcn_size_bits) {
+		ntfs_error(sb,
+			"Child node vcn %lld is outside $INDEX_ALLOCATION in directory inode 0x%llx.",
+			vcn, dir_ni->mft_no);
+		err = -EIO;
+		goto err_out;
+	}
 	/*
 	 * Convert vcn to index into the index allocation attribute in units
 	 * of PAGE_SIZE and map the page cache page, reading it from
-- 
2.53.0