linux-kernel - Re: [PATCH] rpmsg: glink: Release driver

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Message-ID: <20230118175042.GA3322341@hu-bjorande-lv.qualcomm.com>
Date:   Wed, 18 Jan 2023 09:50:42 -0800
From:   Bjorn Andersson <quic_bjorande@...cinc.com>
To:     Chris Lew <quic_clew@...cinc.com>
CC:     Bjorn Andersson <andersson@...nel.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        "open list:ARM/QUALCOMM SUPPORT" <linux-arm-msm@...r.kernel.org>,
        "open list:REMOTE PROCESSOR MESSAGING (RPMSG) SUBSYSTEM" 
        <linux-remoteproc@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] rpmsg: glink: Release driver_override

On Tue, Jan 17, 2023 at 05:01:01PM -0800, Chris Lew wrote:
> 
> 
> On 1/9/2023 2:38 PM, Bjorn Andersson wrote:
> > Upon termination of the rpmsg_device, driver_override needs to be freed
> > to avoid leaking the potentially assigned string.
> > 
> > Fixes: 42cd402b8fd4 ("rpmsg: Fix kfree() of static memory on setting driver_override")
> > Fixes: 39e47767ec9b ("rpmsg: Add driver_override device attribute for rpmsg_device")
> > Signed-off-by: Bjorn Andersson <quic_bjorande@...cinc.com>
> > ---
> >   drivers/rpmsg/qcom_glink_native.c | 2 ++
> >   1 file changed, 2 insertions(+)
> > 
> > diff --git a/drivers/rpmsg/qcom_glink_native.c b/drivers/rpmsg/qcom_glink_native.c
> > index 8620eea1dc8a..046271e439c5 100644
> > --- a/drivers/rpmsg/qcom_glink_native.c
> > +++ b/drivers/rpmsg/qcom_glink_native.c
> > @@ -1454,6 +1454,7 @@ static void qcom_glink_rpdev_release(struct device *dev)
> >   {
> >   	struct rpmsg_device *rpdev = to_rpmsg_device(dev);
> > +	kfree(rpdev->driver_override);
> 
> I see in Krzysztof's original patch to fix up the driver_override we do
> kfree in other areas of rpmsg.
> 

Right, in the original patch what became driver_set_override() was open
coded and hence there was a kfree().

> More of a just curious as to why don't we use the driver_set_override
> function to clear the string? It's mentioned in the rpmsg header that the
> helper should be used.
> 
> --- include/linux/rpmsg.h
>  * @driver_override: driver name to force a match; do not set directly,
>  *                   because core frees it; use driver_set_override() to
>  *                   set or clear it.
> 

Looking around the kernel, just calling kfree() in the release function
seems to be how others are doing it as well. As such I presume that
comment applies to the runtime state, rather than while we're cleaning
things up.

Regards,
Bjorn

> >   	kfree(rpdev);
> >   }
> > @@ -1697,6 +1698,7 @@ static void qcom_glink_device_release(struct device *dev)
> >   	/* Release qcom_glink_alloc_channel() reference */
> >   	kref_put(&channel->refcount, qcom_glink_channel_release);
> > +	kfree(rpdev->driver_override);
> >   	kfree(rpdev);
> >   }
> >