[PATCH] xfs: Fix error pointer dereference

[PATCH] xfs: Fix error pointer dereference

[Ethan Tidmore]

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")
Signed-off-by: Ethan Tidmore <ethantidmore06@gmail.com>
---
 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

Re: [PATCH] xfs: Fix error pointer dereference

[Darrick J. Wong]

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@vger.kernel.org> # v6.16

> Signed-off-by: Ethan Tidmore <ethantidmore06@gmail.com>
> ---
>  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?

> -	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?

--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
> 
> 

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@vger.kernel.org> # 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@gmail.com>
> > ---
> >  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
> > 
> > 
> 

Re: [PATCH] xfs: Fix error pointer dereference

[Darrick J. Wong]

On Thu, Feb 19, 2026 at 11:25:38AM +1100, NeilBrown wrote:
> 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@vger.kernel.org> # v6.16
> 
> I don't think this is justified.  In this use case try_lookup_noperm()
> will never actually return an error.

Sure, but a future update to try_lookup_noperm that *does* introduce the
possibility of an ERR_PTR return could get backported to 6.18, at which
point this code is now broken.  I think I'd rather just clean all this
up all at once.

> > 
> > > Signed-off-by: Ethan Tidmore <ethantidmore06@gmail.com>
> > > ---
> > >  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.

If we're going to check for an ERR_PTR value (even if one cannot
currently be returned) then we should pass it upwards.  We might as well
get rid of all the lurking broken logic all at once.

--D

> 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
> > > 
> > > 
> > 
> 
> 

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@gmail.com>
> ---
>  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
> 
> 

Re: [PATCH] xfs: Fix error pointer dereference

[Nirjhar Roy (IBM)]

On Wed, 2026-02-18 at 13:51 -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.

Nit:In the subject, maybe just add the function name where the error pointer dereference is being
fixed?
> 
> 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")
> Signed-off-by: Ethan Tidmore <ethantidmore06@gmail.com>
> ---
>  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);

Based on my limited knowledge of this change looks okay to me. I looked into the return values of
try_lookup_noperm() and it does return error pointer which is not NULL. I also checked the other
call sites of try_lookup_noperm() but I do see a mixed handling i.e, some places just checks for
!ptr and some for IS_ERR_OR_NULL. For example in fs/autofs it checks with IS_ERR_OR_NULL whereas in
fs/proc/base.c it just checks for !child. However, IMO, it is better to check for both NULL and
error pointer if there is a possibility for both.
--NR
>  
>  		ASSERT(d_is_negative(d_child));

Re: [PATCH] xfs: Fix error pointer dereference

[Ethan Tidmore]

On Thu Feb 19, 2026 at 5:26 AM CST, Nirjhar Roy (IBM) wrote:
> On Wed, 2026-02-18 at 13:51 -0600, Ethan Tidmore wrote:

...

>
> Based on my limited knowledge of this change looks okay to me. I looked into the return values of
> try_lookup_noperm() and it does return error pointer which is not NULL. I also checked the other
> call sites of try_lookup_noperm() but I do see a mixed handling i.e, some places just checks for
> !ptr and some for IS_ERR_OR_NULL. For example in fs/autofs it checks with IS_ERR_OR_NULL whereas in
> fs/proc/base.c it just checks for !child. However, IMO, it is better to check for both NULL and
> error pointer if there is a possibility for both.
> --NR

I was already planning on sending a patch to fs/proc/base.c also. Smatch
was complaining there too.

Thanks,

ET