RE: [PATCH] platform/mellanox: mlxreg-hotplug: Check pointer for NULL before dereferencing it

[Vadim Pasternak]

> -----Original Message-----
> From: Daniil Dulov <D.Dulov@xxxxxxxxxx>
> Sent: Monday, 4 March 2024 13:44
> To: Vadim Pasternak <vadimp@xxxxxxxxxx>; Hans de Goede
> <hdegoede@xxxxxxxxxx>
> Cc: Mark Gross <mgross@xxxxxxxxxxxxxxx>; Andy Shevchenko
> <andy@xxxxxxxxxxxxx>; Darren Hart <dvhart@xxxxxxxxxxxxx>; platform-
> driver-x86@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; lvc-
> project@xxxxxxxxxxxxxxxx
> Subject: RE: [PATCH] platform/mellanox: mlxreg-hotplug: Check pointer for
> NULL before dereferencing it
> 
> Hello!
> 
> I suppose there is no sense to produce dev_err() inside
> mlxreg_hotplug_work_helper() since item is dereferenced twice before we
> call this function. Should we produce dev_err() inside the loop in
> mlxreg_hotplug_work_handler() instead?

Hi Daniil,

I think would be correct just to remove from mlx reg_hotplug_work_helper()
lines validating 'item' pointer.
This is paranoic test, this pointer should never be NULL.
It is safe to remove this validation.

Thanks,
Vadim.

> 
> -----Original Message-----
> From: Vadim Pasternak [mailto:vadimp@xxxxxxxxxx]
> Sent: Monday, February 26, 2024 6:15 PM
> To: Daniil Dulov <D.Dulov@xxxxxxxxxx>; Hans de Goede
> <hdegoede@xxxxxxxxxx>
> Cc: Mark Gross <mgross@xxxxxxxxxxxxxxx>; Andy Shevchenko
> <andy@xxxxxxxxxxxxx>; Darren Hart <dvhart@xxxxxxxxxxxxx>; platform-
> driver-x86@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; lvc-
> project@xxxxxxxxxxxxxxxx
> Subject: RE: [PATCH] platform/mellanox: mlxreg-hotplug: Check pointer for
> NULL before dereferencing it
> 
> 
> 
> > -----Original Message-----
> > From: Daniil Dulov <d.dulov@xxxxxxxxxx>
> > Sent: Monday, 26 February 2024 16:55
> > To: Hans de Goede <hdegoede@xxxxxxxxxx>
> > Cc: Daniil Dulov <d.dulov@xxxxxxxxxx>; Mark Gross
> > <mgross@xxxxxxxxxxxxxxx>; Andy Shevchenko <andy@xxxxxxxxxxxxx>;
> Darren
> > Hart <dvhart@xxxxxxxxxxxxx>; Vadim Pasternak <vadimp@xxxxxxxxxx>;
> > platform-driver-x86@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; lvc-
> > project@xxxxxxxxxxxxxxxx
> > Subject: [PATCH] platform/mellanox: mlxreg-hotplug: Check pointer for NULL
> > before dereferencing it
> >
> > mlxreg_hotplug_work_helper() implies that item can be NULL. There is a
> > sanity check that checks item for NULL and then dereferences it.
> >
> > Even though, the comment before sanity check says that it can only happen
> if
> > some piece of hardware is broken, but in this case it will lead to NULL-
> pointer
> > dereference before the function is even called, so let's check it before
> > dereferencing.
> >
> > Found by Linux Verification Center (linuxtesting.org) with SVACE.
> >
> > Fixes: c6acad68eb2d ("platform/mellanox: mlxreg-hotplug: Modify to use a
> > regmap interface")
> > Signed-off-by: Daniil Dulov <d.dulov@xxxxxxxxxx>
> > ---
> >  drivers/platform/mellanox/mlxreg-hotplug.c | 16 +---------------
> >  1 file changed, 1 insertion(+), 15 deletions(-)
> >
> > diff --git a/drivers/platform/mellanox/mlxreg-hotplug.c
> > b/drivers/platform/mellanox/mlxreg-hotplug.c
> > index 5c022b258f91..524121b9f070 100644
> > --- a/drivers/platform/mellanox/mlxreg-hotplug.c
> > +++ b/drivers/platform/mellanox/mlxreg-hotplug.c
> > @@ -348,20 +348,6 @@ mlxreg_hotplug_work_helper(struct
> > mlxreg_hotplug_priv_data *priv,
> >  	u32 regval, bit;
> >  	int ret;
> >
> > -	/*
> > -	 * Validate if item related to received signal type is valid.
> > -	 * It should never happen, excepted the situation when some
> > -	 * piece of hardware is broken. In such situation just produce
> > -	 * error message and return. Caller must continue to handle the
> > -	 * signals from other devices if any.
> > -	 */
> > -	if (unlikely(!item)) {
> > -		dev_err(priv->dev, "False signal: at offset:mask
> > 0x%02x:0x%02x.\n",
> > -			item->reg, item->mask);
> > -
> > -		return;
> > -	}
> 
> It would be enough just to produce dev_err(priv->dev, "False signal\n");
> And return.
> 
> > -
> >  	/* Mask event. */
> >  	ret = regmap_write(priv->regmap, item->reg +
> > MLXREG_HOTPLUG_MASK_OFF,
> >  			   0);
> > @@ -556,7 +542,7 @@ static void mlxreg_hotplug_work_handler(struct
> > work_struct *work)
> >
> >  	/* Handle topology and health configuration changes. */
> >  	for (i = 0; i < pdata->counter; i++, item++) {
> > -		if (aggr_asserted & item->aggr_mask) {
> > +		if (item && (aggr_asserted & item->aggr_mask)) {
> >  			if (item->health)
> >  				mlxreg_hotplug_health_work_helper(priv,
> > item);
> >  			else
> > --
> > 2.25.1