Re: [PATCH] ipmi: kcs_bmc: Fix a memory leak in the error handling path of 'kcs_bmc_serio_add_device()'

[Marion et Christophe JAILLET]

> Message du 08/09/21 08:28
> De : "Dan Carpenter" 
> A : "Christophe JAILLET" 
> Copie à : minyard@xxxxxxx, zweiss@xxxxxxxxxxx, andrew@xxxxxxxx, openipmi-developer@xxxxxxxxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, kernel-janitors@xxxxxxxxxxxxxxx
> Objet : Re: [PATCH] ipmi: kcs_bmc: Fix a memory leak in the error handling path of 'kcs_bmc_serio_add_device()'
> 
> On Tue, Sep 07, 2021 at 11:06:32PM +0200, Christophe JAILLET wrote:
> > In the unlikely event where 'devm_kzalloc()' fails and 'kzalloc()'
> > succeeds, 'port' would be leaking.
> > 
> > Test each allocation separately to avoid the leak.
> > 
> > Fixes: 3a3d2f6a4c64 ("ipmi: kcs_bmc: Add serio adaptor")
> > Signed-off-by: Christophe JAILLET 
> > ---
> > drivers/char/ipmi/kcs_bmc_serio.c | 4 +++-
> > 1 file changed, 3 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/char/ipmi/kcs_bmc_serio.c b/drivers/char/ipmi/kcs_bmc_serio.c
> > index 7948cabde50b..7e2067628a6c 100644
> > --- a/drivers/char/ipmi/kcs_bmc_serio.c
> > +++ b/drivers/char/ipmi/kcs_bmc_serio.c
> > @@ -73,10 +73,12 @@ static int kcs_bmc_serio_add_device(struct kcs_bmc_device *kcs_bmc)
> > struct serio *port;
> > 
> > priv = devm_kzalloc(kcs_bmc->dev, sizeof(*priv), GFP_KERNEL);
> > + if (!priv)
> > + return -ENOMEM;
> > 
> > /* Use kzalloc() as the allocation is cleaned up with kfree() via serio_unregister_port() */
> 
> The serio_unregister_port() calls serio_destroy_port() which calls
> put_device(&serio->dev). But I wasn't able to track it further than
> that to the actual kfree().

Hi Dan,

Checking this release path was not the goal of this patch.
It was only about the VERRYYYY unlikely memory leak.

However my understanding is:
kcs_bmc_serio_add_device
--> serio_register_port
--> __serio_register_port
--> serio_init_port
--> serio->dev.release = serio_release_port

And in serio_release_port:
struct serio *serio = to_serio_port(dev);
kfree(serio);

For me, this 'serio' looks to the one allocated by 'kcs_bmc_serio_add_device'.
I think that the comment is correct.

CJ

> 
> Is there a trick to finding ->release() functions?
> 
> regards,
> dan carpenter
> 
> 
>