Re: [PATCH] fs/ntfs3: fix wrong LCN in run_remove_range() when splitting a run

[Konstantin Komarov <almaz.alexandrovich@paragon-software.com>]

On 5/8/26 11:52, Zhan Xusheng wrote:

> When run_remove_range() removes a middle portion of a non-sparse run,
> it splits the run into head and tail parts.  The tail is inserted via
> run_add_entry() but uses the original r->lcn as its starting LCN
> instead of advancing it by the split offset.
>
> For example, removing VCN range [10, 20) from a run
> {vcn=0, lcn=100, len=30} should produce:
>    {vcn=0,  lcn=100, len=10}   (head)
>    {vcn=20, lcn=120, len=10}   (tail, lcn advanced by 20)
>
> But the current code produces:
>    {vcn=0,  lcn=100, len=10}
>    {vcn=20, lcn=100, len=10}   (wrong: points to same physical clusters)
>
> This creates overlapping physical mappings in the in-memory run tree,
> which can corrupt cluster allocation decisions and lead to data
> corruption.
>
> The correct pattern is already used in run_insert_range():
>    CLST lcn2 = r->lcn == SPARSE_LCN ? SPARSE_LCN : (r->lcn + len1);
>
> Apply the same logic in run_remove_range().
>
> Fixes: 10d7c95af043 ("fs/ntfs3: add delayed-allocation (delalloc) support")
> Signed-off-by: Zhan Xusheng <zhanxusheng@xiaomi.com>
> ---
>   fs/ntfs3/run.c | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/fs/ntfs3/run.c b/fs/ntfs3/run.c
> index 1ce7d92fb274..cca6bdf2e7aa 100644
> --- a/fs/ntfs3/run.c
> +++ b/fs/ntfs3/run.c
> @@ -1292,9 +1292,12 @@ bool run_remove_range(struct runs_tree *run, CLST vcn, CLST len, CLST *done)
>   
>   		if (r_end > end) {
>   			/* Remove a middle part, split. */
> +			CLST tail_lcn = r->lcn == SPARSE_LCN ?
> +					SPARSE_LCN : (r->lcn + (end - r->vcn));
> +
>   			*done += len;
>   			r->len = d;
> -			return run_add_entry(run, end, r->lcn, r_end - end,
> +			return run_add_entry(run, end, tail_lcn, r_end - end,
>   					     false);
>   		}
>   		/* Remove tail of run .*/

Hello,

Queued for the next merge window, thank you.

Regards,
Konstantin