Re: [PATCH v2] powerpc/mpic: Fix memory leak of mpic on error paths

[Jyoti Gupta <jyoti@linux.ibm.com>]

Hi Amit ,

Please refer to my inline comments below.

On 2026-10-05 13:14, Amit Machhiwal wrote:
> Hi Jyoti,
> 
> Please find my responses inline below.
> 
> On 2026/10/01 05:29 PM, Jyoti Gupta wrote:
>> On 2026-10-01 00:20, Amit Machhiwal wrote:
>> > On 2026/09/30 11:39 PM, Jyoti Gupta wrote:
>> > > mpic_alloc() allocates struct mpic (and optionally the protected
>> > > sources bitmap) but does not free them when mpic_setup_error_int() or
>> > > irq_domain_create_linear() fails, leaking the memory.
>> > >
>> > > Free the bitmap and the mpic in the common error path before
>> > > dropping the
>> > > device node reference.
>> > >
>> > > Fixes: 996983b75ceb ("powerpc/mpic: Search for open-pic device-tree
>> > > node if NULL")
>> > > Signed-off-by: Jyoti Gupta <jyoti@linux.ibm.com>
>> > > ---
>> > >  arch/powerpc/sysdev/mpic.c | 11 +++++------
>> > >  1 file changed, 5 insertions(+), 6 deletions(-)
>> >
>> > Thanks for addressing the comments from v1.
>> >
>> > A couple of minor suggestions:
>> >
>> > 1. Changelog & Links: It is always a good practice to include a
>> > changelog below
>> >    the "---" line detailing the changes made in this version (e.g. "v1
>> > -> v2:
>> >    ...") along with a link to the previous version(s) on
>> > lore.kernel.org. This
>> >    helps reviewers and maintainers quickly track the evolution of the
>> > patch.
>> >
>> 
>> Got it, thank you for the suggestion. I'll keep it in mind.
>> 
>> > 2. Minor nit in cleanup logic below:
>> >
>> > >
>> > > diff --git a/arch/powerpc/sysdev/mpic.c b/arch/powerpc/sysdev/mpic.c
>> > > index 257886ec3f70..b21a880777cc 100644
>> > > --- a/arch/powerpc/sysdev/mpic.c
>> > > +++ b/arch/powerpc/sysdev/mpic.c
>> > > @@ -1389,7 +1389,7 @@ struct mpic * __init mpic_alloc(struct
>> > > device_node *node,
>> > >  		if (fsl_version >= 0x401) {
>> > >  			ret = mpic_setup_error_int(mpic, intvec_top - 13);
>> > >  			if (ret)
>> > > -				return NULL;
>> > > +				goto err_of_node_put;
>> > >  		}
>> > >
>> > >  	}
>> > > @@ -1488,12 +1488,8 @@ struct mpic * __init mpic_alloc(struct
>> > > device_node *node,
>> > >  						 intvec_top,
>> > >  						 &mpic_host_ops, mpic);
>> > >
>> > > -	/*
>> > > -	 * FIXME: The code leaks the MPIC object and mappings here; this
>> > > -	 * is very unlikely to fail but it ought to be fixed anyways.
>> > > -	 */
>> > >  	if (mpic->irqhost == NULL)
>> > > -		return NULL;
>> > > +		goto err_of_node_put;
>> > >
>> > >  	/* Display version */
>> > >  	switch (greg_feature & MPIC_GREG_FEATURE_VERSION_MASK) {
>> > > @@ -1527,6 +1523,9 @@ struct mpic * __init mpic_alloc(struct
>> > > device_node *node,
>> > >  	return mpic;
>> > >
>> > >  err_of_node_put:
>> > > +	if (mpic)
>> > > +		bitmap_free(mpic->protected);
>> > > +	kfree(mpic);
>> >
>> > Both bitmap_free() and kfree() safely handle NULL pointers (and mpic is
>> > guaranteed to be non-NULL at this label anyway), so the 'if (mpic)'
>> > check is
>> > redundant.
>> >
>> 
>> Thanks for the review.
>> 
>> Regarding the 'if (mpic)' check, I think we may need to keep it. While
>> bitmap_free() and kfree() both safely handle NULL, the concern here is
>> dereferencing mpic to obtain mpic->protected. There are two paths that
>> reach err_of_node_put before mpic is allocated (line 1276):
>> of_address_to_resource() failure at line 1258 and kzalloc_obj() 
>> returning
>> NULL at line 1278. In both cases, mpic->protected would dereference a
>> NULL/garbage pointer and crash.
> 
> Good catch on the early error paths before mpic allocation!
> 
> However, in v2, 'struct mpic *mpic' is left uninitialized at function 
> entry
> (since the '= NULL' initialization was dropped).
> 
> Looking more closely, if of_address_to_resource() fails at line 1258, 
> control
> jumps to err_of_node_put where 'mpic' contains uninitialized stack 
> garbage.  In
> that case, 'if (mpic)' evaluates to true, leading to an invalid pointer
> dereference when evaluating mpic->protected and a crash on kfree(mpic).
> 
> Rather than initializing mpic to NULL and checking 'if (mpic)' on error 
> paths,
> the preferred approach in Linux is to use layered error labels.  In 
> fact,
> Documentation/process/coding-style.rst (Section 7, "Centralized exiting 
> of
> functions") specifically describes this pattern when discussing "one 
> err bugs":
> 
> 
>   A common type of bug to be aware of is ``one err bugs`` which look 
> like this:
> 
>   .. code-block:: c
> 
>   	err:
>   		kfree(foo->bar);
>   		kfree(foo);
>   		return ret;
> 
>   The bug in this code is that on some exit paths ``foo`` is NULL.  
> Normally the
>   fix for this is to split it up into two error labels 
> ``err_free_bar:`` and
>   ``err_free_foo:``:
> 
>   .. code-block:: c
> 
>   	err_free_bar:
>   		kfree(foo->bar);
>   	err_free_foo:
>   		kfree(foo);
>   		return ret;
> 
> Applying that pattern here gives:
> 
> diff --git a/arch/powerpc/sysdev/mpic.c b/arch/powerpc/sysdev/mpic.c
> index 257886ec3f70..d799cf4da7bd 100644
> --- a/arch/powerpc/sysdev/mpic.c
> +++ b/arch/powerpc/sysdev/mpic.c
> @@ -1389,7 +1389,7 @@ struct mpic * __init mpic_alloc(struct 
> device_node *node,
>                 if (fsl_version >= 0x401) {
>                         ret = mpic_setup_error_int(mpic, intvec_top - 
> 13);
>                         if (ret)
> -                               return NULL;
> +                               goto err_free_mpic;
>                 }
> 
>         }
> @@ -1488,12 +1488,8 @@ struct mpic * __init mpic_alloc(struct 
> device_node *node,
>                                                  intvec_top,
>                                                  &mpic_host_ops, mpic);
> 
> -       /*
> -        * FIXME: The code leaks the MPIC object and mappings here; 
> this
> -        * is very unlikely to fail but it ought to be fixed anyways.
> -        */
>         if (mpic->irqhost == NULL)
> -               return NULL;
> +               goto err_free_mpic;
> 
>         /* Display version */
>         switch (greg_feature & MPIC_GREG_FEATURE_VERSION_MASK) {
> @@ -1526,6 +1522,9 @@ struct mpic * __init mpic_alloc(struct 
> device_node *node,
> 
>         return mpic;
> 
> +err_free_mpic:
> +       bitmap_free(mpic->protected);
> +       kfree(mpic);
>  err_of_node_put:
>         of_node_put(node);
>         return NULL;
> 
> This ensures:
> 
> 1. Early error paths (of_address_to_resource and kzalloc_obj failures) 
> jump
>    directly to err_of_node_put without touching mpic.
> 2. Later error paths jump to err_free_mpic where mpic is guaranteed to 
> be valid.
> 3. No 'if (mpic)' check or 'struct mpic *mpic = NULL;' is needed.
> 

Thank you for the detailed explanation.

> What do you think?
> 

Yes, this sounds more accurate — the layered error labels are clearly 
the right approach here. Will fix it in v3.


Thanks,
Jyoti