Re: [PATCH] xfs: Fix error pointer dereference

[NeilBrown]

On Thu, 19 Feb 2026, Ethan Tidmore wrote:
> The function try_lookup_noperm() can return an error pointer and is not
> checked for one. Add checks for error pointer.
> 
> Detected by Smatch:
> fs/xfs/scrub/orphanage.c:449 xrep_adoption_check_dcache() error: 
> 'd_child' dereferencing possible ERR_PTR()
> 
> fs/xfs/scrub/orphanage.c:485 xrep_adoption_zap_dcache() error: 
> 'd_child' dereferencing possible ERR_PTR()
> 
> Fixes: 06c567403ae5a ("Use try_lookup_noperm() instead of d_hash_and_lookup() outside of VFS")

This commit didn't introduce this behaviour.
It changed from using d_hash_and_lookup() to using try_lookup_noperm().

Both can return an ERR_PTR().  Neither ever do in this code.

As the lookup only happens in an XFS filesystem and as XFS doesn't
define d_hash(), d_hash_and_lookup() would never actually return an
error.

try_lookup_noperm() does add some error cases for, e.g.  , "." and ".."
and names containing "/".  But none of these apply here.

So this is worth fixing, but the current code has been like this since
it was written, so

Fixes: 73597e3e42b4 ("xfs: ensure dentry consistency when the orphanage adopts a file")

would be more appropriate.

Thanks,
NeilBrown


> Signed-off-by: Ethan Tidmore <ethantidmore06@xxxxxxxxx>
> ---
>  fs/xfs/scrub/orphanage.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/xfs/scrub/orphanage.c b/fs/xfs/scrub/orphanage.c
> index 52a108f6d5f4..cdb0f486f50c 100644
> --- a/fs/xfs/scrub/orphanage.c
> +++ b/fs/xfs/scrub/orphanage.c
> @@ -442,7 +442,7 @@ xrep_adoption_check_dcache(
>  		return 0;
>  
>  	d_child = try_lookup_noperm(&qname, d_orphanage);
> -	if (d_child) {
> +	if (!IS_ERR_OR_NULL(d_child)) {
>  		trace_xrep_adoption_check_child(sc->mp, d_child);
>  
>  		if (d_is_positive(d_child)) {
> @@ -479,7 +479,7 @@ xrep_adoption_zap_dcache(
>  		return;
>  
>  	d_child = try_lookup_noperm(&qname, d_orphanage);
> -	while (d_child != NULL) {
> +	while (!IS_ERR_OR_NULL(d_child)) {
>  		trace_xrep_adoption_invalidate_child(sc->mp, d_child);
>  
>  		ASSERT(d_is_negative(d_child));
> -- 
> 2.53.0
> 
>