Re: [PATCH] xfs: Fix error pointer dereference

[NeilBrown]

On Thu, 19 Feb 2026, Darrick J. Wong wrote:
> On Wed, Feb 18, 2026 at 01:51:15PM -0600, 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")
> 
> Cc: <stable@xxxxxxxxxxxxxxx> # v6.16

I don't think this is justified.  In this use case try_lookup_noperm()
will never actually return an error.

> 
> > 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);
> 
> "Look up a dentry by name in the dcache, returning NULL if it does not
> currently exist."
> 
> Could you please fix the documentation since try_lookup_noperm can
> return ERR_PTR values?

Fair - I'll include a patch with my next batch.

> 
> > -	if (d_child) {
> > +	if (!IS_ERR_OR_NULL(d_child)) {
> 
> If d_child is an ERR_PTR, shouldn't we extract that error value and
> return it instead of zero?

This is a purely cosmetic question as no error is actually returned in
practice.  So whatever you feel most comfortable with is best.

NeilBrown


> 
> --D
> 
> >  		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
> > 
> > 
>