Re: [PATCH] ntfs: exclude DOS aliases from VFS link count

[liubaolin <liubaolin12138@163.com>]

在 2026/9/24 12:17, Michael Woolweaver 写道:
> NTFS counts each $FILE_NAME attribute in the MFT record link_count.
> A file with separate Win32 and DOS 8.3 names therefore has a link_count
> of two even though the DOS name is an alias and does not represent a
> separate VFS hard link.
> 
> ntfs_read_locked_inode() copies the MFT link_count directly to i_nlink,
> causing stat() to report an extra hard link for files with a separate
> DOS alias.
> 
> The same distinction is needed when unlinking. ntfs_delete() removes
> both the DOS and Win32 $FILE_NAME attributes, decrementing the on-disk
> link_count for each, but it must decrement the VFS link count only for
> the Win32 name. Otherwise a real hard link can reach i_nlink zero while
> another VFS-visible name still exists.
> 
> Count non-DOS $FILE_NAME attributes when initializing i_nlink, while
> still verifying that the MFT link_count matches the total number of
> name attributes. Do not drop i_nlink when ntfs_delete() removes a DOS
> alias.
> 
> This was reproduced with a file containing separate Win32 and DOS
> names. Its MFT link_count was 2 while stat() incorrectly reported 2
> links. With the fix, stat() reports 1.
> 
> After adding a real POSIX hard link, the MFT contained three
> $FILE_NAME attributes while the VFS correctly reported two links.
> Removing the Win32/DOS pair left the POSIX hard link with both the MFT
> link_count and VFS i_nlink equal to 1.
> 
> The fix was runtime-tested with fs/ntfs on a disposable NTFS image and
> compile-tested on ntfs-next with W=1. checkpatch.pl reports no issues.
> 
> Fixes: 1e9ea7e04472 ("Revert "fs: Remove NTFS classic"")
> Assisted-by: LLM
> Signed-off-by: Michael Woolweaver <michael@woolweaver.bid>
> ---
>   fs/ntfs/inode.c | 77 +++++++++++++++++++++++++++++++++++++++++++++++++
>   fs/ntfs/namei.c |  5 +++-
>   2 files changed, 81 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/ntfs/inode.c b/fs/ntfs/inode.c
> index 9583b2c6c7a2..74a0d9d1e82b 100644
> --- a/fs/ntfs/inode.c
> +++ b/fs/ntfs/inode.c
> @@ -621,6 +621,67 @@ static int ntfs_is_extended_system_file(struct ntfs_attr_search_ctx *ctx)
>   	return 0;	/* NO, it is not an extended system file. */
>   }
>   
> +/*
> + * ntfs_count_vfs_links - count VFS-visible hard links
> + * @ctx: initialized attribute search context
> + *
> + * The MFT link count counts all $FILE_NAME attributes.  A separate DOS 8.3
> + * name therefore contributes to the on-disk count even though it is an alias
> + * for its Win32 name and does not represent another VFS hard link.
> + *
> + * Return the number of VFS-visible links or -errno on error.
> + */
> +static int ntfs_count_vfs_links(struct ntfs_attr_search_ctx *ctx)
> +{
> +	unsigned int expected, names = 0, links = 0;
> +	int err;
> +
> +	expected = le16_to_cpu(ctx->mrec->link_count);
> +	ntfs_attr_reinit_search_ctx(ctx);

Hi Michael,
   Could we reinitialize the search context before reading link_count?

   ntfs_attr_reinit_search_ctx(ctx);
   expected = le16_to_cpu(ctx->mrec->link_count);

   This ensures the count is read from the base MFT record even if the 
incoming context points to an extent record.

Thanks,
Baolin.

> +
> +	while (!(err = ntfs_attr_lookup(AT_FILE_NAME, NULL, 0, 0, 0, NULL, 0,
> +					ctx))) {
> +		struct attr_record *attr = ctx->attr;
> +		struct file_name_attr *fn;
> +		u32 attr_len, value_len;
> +		u16 value_off;
> +
> +		if (unlikely(attr->non_resident))
> +			goto corrupt;
> +
> +		attr_len = le32_to_cpu(attr->length);
> +		value_len = le32_to_cpu(attr->data.resident.value_length);
> +		value_off = le16_to_cpu(attr->data.resident.value_offset);
> +
> +		if (unlikely(value_off > attr_len ||
> +			     value_len > attr_len - value_off ||
> +			     value_len < offsetof(struct file_name_attr, file_name)))
> +			goto corrupt;
> +
> +		fn = (struct file_name_attr *)((u8 *)attr + value_off);
> +		names++;
> +		if (fn->file_name_type != FILE_NAME_DOS)
> +			links++;
> +	}
> +
> +	if (unlikely(err != -ENOENT))
> +		return err;
> +
> +	if (unlikely(names != expected || !links)) {
> +		ntfs_error(ctx->ntfs_ino->vol->sb,
> +			   "Inode link count doesn't match file name attributes. You should run chkdsk.");
> +		return -EIO;
> +	}
> +
> +	ntfs_attr_reinit_search_ctx(ctx);
> +	return links;
> +
> +corrupt:
> +	ntfs_error(ctx->ntfs_ino->vol->sb,
> +		   "Corrupt file name attribute. You should run chkdsk.");
> +	return -EIO;
> +}
> +
>   static struct lock_class_key ntfs_dir_inval_lock_key;
>   
>   void ntfs_set_vfs_operations(struct inode *inode, mode_t mode, dev_t dev)
> @@ -872,6 +933,22 @@ static int ntfs_read_locked_inode(struct inode *vi)
>   		}
>   	}
>   skip_attr_list_load:
> +	/*
> +	 * The MFT link count includes separate DOS 8.3 aliases.  Once the
> +	 * attribute list is available, derive the VFS link count from the
> +	 * $FILE_NAME namespaces instead.
> +	 */
> +	if (!(m->flags & MFT_RECORD_IS_DIRECTORY) && vi->i_ino != FILE_MFT) {
> +		int nr_links;
> +
> +		nr_links = ntfs_count_vfs_links(ctx);
> +		if (unlikely(nr_links < 0)) {
> +			err = nr_links;
> +			goto unm_err_out;
> +		}
> +		set_nlink(vi, nr_links);
> +	}
> +
>   	err = ntfs_attr_lookup(AT_EA_INFORMATION, NULL, 0, 0, 0, NULL, 0, ctx);
>   	if (!err) {
>   		NInoSetHasEA(ni);
> diff --git a/fs/ntfs/namei.c b/fs/ntfs/namei.c
> index 75e201096525..891ee697c0d2 100644
> --- a/fs/ntfs/namei.c
> +++ b/fs/ntfs/namei.c
> @@ -829,6 +829,7 @@ static int ntfs_delete(struct ntfs_inode *ni, struct ntfs_inode *dir_ni,
>   	struct file_name_attr *fn = NULL;
>   	bool looking_for_dos_name = false, looking_for_win32_name = false;
>   	bool case_sensitive_match = true;
> +	bool is_dos_name;
>   	int err = 0;
>   	struct mft_record *ni_mrec;
>   	struct super_block *sb;
> @@ -932,6 +933,8 @@ static int ntfs_delete(struct ntfs_inode *ni, struct ntfs_inode *dir_ni,
>   	if (err)
>   		goto err_out;
>   
> +	is_dos_name = fn->file_name_type == FILE_NAME_DOS;
> +
>   	err = ntfs_index_remove(dir_ni, fn, le32_to_cpu(actx->attr->data.resident.value_length));
>   	if (err)
>   		goto err_out;
> @@ -942,7 +945,7 @@ static int ntfs_delete(struct ntfs_inode *ni, struct ntfs_inode *dir_ni,
>   
>   	ni_mrec = actx->base_mrec ? actx->base_mrec : actx->mrec;
>   	ni_mrec->link_count = cpu_to_le16(le16_to_cpu(ni_mrec->link_count) - 1);
> -	if (!S_ISDIR(VFS_I(ni)->i_mode))
> +	if (!S_ISDIR(VFS_I(ni)->i_mode) && !is_dos_name)
>   		drop_nlink(VFS_I(ni));
>   
>   	mark_mft_record_dirty(ni);
> 
> base-commit: 401898d748fcc8e19ceea1a37ed0de9075fe9ff2