[PATCH] ntfs3: fix out-of-bounds read in ntfs_read_mft()

ntfs_read_mft() walks the attributes of an MFT record and, for each
FILE_NAME attribute, compares the resident on-disk name with the name
being looked up.  The only size check before the compare is
rsize >= SIZEOF_ATTRIBUTE_FILENAME, which covers the fixed header up to
and including name_len, but not the variable-length name that follows it.

name_len comes straight from disk and is not validated against the
resident data_size.  A crafted image can set name_len large while keeping
data_size at the header size, so ntfs_cmp_names_cpu() reads name_len
le16 characters past the end of the MFT record buffer:

  BUG: KASAN: slab-out-of-bounds in ntfs_cmp_names_cpu (fs/ntfs3/upcase.c:84)
  Read of size 2 at addr ffff888031879c00 by task a.out
   ntfs_cmp_names_cpu (fs/ntfs3/upcase.c:84)
   ntfs_iget5 (fs/ntfs3/inode.c:209)
   dir_search_u (fs/ntfs3/dir.c:265)
   ntfs_lookup (fs/ntfs3/namei.c:85)
   __lookup_slow (fs/namei.c:1915)
   lookup_slow (fs/namei.c:1932)
   path_lookupat (fs/namei.c:2278)
   vfs_statx (fs/stat.c)
   vfs_fstatat (fs/stat.c)
   __do_sys_newfstatat (fs/stat.c)

  Allocated by task:
   mi_init (fs/ntfs3/record.c)
   ntfs_iget5 (fs/ntfs3/inode.c)
   dir_search_u (fs/ntfs3/dir.c)
   ntfs_lookup (fs/ntfs3/namei.c)

Check that the name fits in the resident data before using it.

Fixes: 82cae269cfa9 ("fs/ntfs3: Add initialization of super block")
Reported-by: Xiang Mei <[email protected]>
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Weiming Shi <[email protected]>
---
 fs/ntfs3/inode.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/fs/ntfs3/inode.c b/fs/ntfs3/inode.c
index c43101cc064d..c41c7231bb87 100644
--- a/fs/ntfs3/inode.c
+++ b/fs/ntfs3/inode.c
@@ -201,6 +201,11 @@ static struct inode *ntfs_read_mft(struct inode *inode,
 
 		names += 1;
 		fname = Add2Ptr(attr, roff);
+
+		/* Make sure the full name fits in the resident data. */
+		if (rsize < fname_full_size(fname))
+			goto out;
+
 		if (fname->type == FILE_NAME_DOS)
 			goto next_attr;
 
-- 
2.43.0