Re: [PATCH v2] fs/ntfs: Fix index_root heap OOB write in ntfs_ir_to_ib()

[Namjae Jeon]

On Fri, Jul 17, 2026 at 7:52 PM Alexandro Calò
<alexandro.calo@xxxxxxxxxxxxxxxxxx> wrote:
>
> From: Alexandro Calo <alexandro.calo@xxxxxxxxxxxxxxxxxx>
> Date: Fri, 17 Jul 2026 12:14:51 +0200
> Subject: [PATCH v2] fs/ntfs: Fix index_root heap OOB write in ntfs_ir_to_ib()
>
> ntfs_ir_to_ib copies all entries from index_root into a freshly allocated
> index_block_size-byte buffer without verifying that the entries fit in the
> available space. The entries in index_root may be larger than the usable
> entry space in the index block.
>
> This can cause OOB writes past the end of the allocation.
>
> The validator ntfs_index_root_inconsistent() checks that entries are
> self-consistent within the IR value, but never cross-checks them against
> index_block_size. There is no bounds check in ntfs_ir_to_ib() before the
> memcpy.
>
> Fixing this at the sink in ntfs_ir_to_ib() since
> ntfs_index_root_inconsistent() validates the logical consistency of
> index_root as a structure and a root with large entries is a structurally
> valid root. The bug is a size conflict of ntfs_ir_to_ib().
> Also, the validator is called once per inode load in
> ntfs_read_locked_inode() while ntfs_ir_to_ib() is only called during a
> reparent, a check there adds no overhead to the common path.
> Moreover, even a future call path that bypasses the validator would still
> be protected.
>
> With NULL as first parameter of ntfs_error(), the volume error flag is
> never set by this call, so the device name will be absent from the error
> message. In any case, that the caller, ntfs_ir_reparent(), prints an error
> message that includes the device name on NULL returns.
> I think this is the best solution available without adding
> 'struct super_block *sb' as a parameter to ntfs_ir_to_ib().
>
> This heap out-of-bounds write is triggered by a crafted filesystem image,
> which is not in the kernel threat model, anyway, fixing memory errors would
> be nice to keep  things secure.
>
> Signed-off-by: Alexandro Calo <alexandro.calo@xxxxxxxxxxxxxxxxxx>
Applied it to #ntfs-next.
Thanks!