Re: [PATCH v2] ntfs: bound $AttrDef table walk to the loaded table size

[Namjae Jeon]

On Wed, Aug 26, 2026 at 1:44 PM Dennis Tighe <dennis.tighe@xxxxxxxxx> wrote:
>
> ntfs_attr_find_in_attrdef() walks the in-memory $AttrDef table, but the
> loop condition bounds only the start of each entry, not the whole entry:
>
>         for (ad = vol->attrdef; (u8 *)ad - (u8 *)vol->attrdef <
>                         vol->attrdef_size && ad->type; ++ad)
>
> struct attr_def is 160 bytes; the guard reads ad->type at offset 128 and
> the loop body reads further fields. vol->attrdef is kvzalloc(i_size),
> where i_size is the on-disk $AttrDef data size, checked in
> load_and_init_attrdef() only as 0 < i_size <= 0x7fffffff. A volume whose
> $AttrDef data size is smaller than one entry (e.g. 120 bytes) makes the
> read of ad->type run past the allocation. Creating a file reaches this
> through ntfs_attr_size_bounds_check() and reads out of bounds:
>
>   BUG: KASAN: slab-out-of-bounds in ntfs_attr_find_in_attrdef+0x66/0xa0
>   Read of size 4 at addr ffff888005833280 by task init/1
>    ntfs_attr_find_in_attrdef
>    ntfs_attr_size_bounds_check
>    ntfs_attr_can_be_non_resident
>    ntfs_attr_add
>
> Require the whole entry to lie within attrdef_size in the loop guard, and
> reject at mount a $AttrDef too small to hold one attr_def entry.
>
> Fixes: 1e9ea7e04472 ("Revert "fs: Remove NTFS classic"")
> Assisted-by: Claude:claude-opus-4-8
> Signed-off-by: Dennis Tighe <dennis.tighe@xxxxxxxxx>
Applied it to #ntfs-next.
Thanks!