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Date:   Tue, 25 May 2021 08:19:58 +0200
From:   Mauro Carvalho Chehab <mchehab@kernel.org>
To:     Dongliang Mu <mudongliangabcd@gmail.com>
Cc:     linux-media@vger.kernel.org, linux-kernel@vger.kernel.org,
        syzbot+e1de8986786b3722050e@syzkaller.appspotmail.com
Subject: Re: [PATCH] media: dvd_usb: memory leak in cinergyt2_fe_attach
Message-ID: <20210525081958.22f1e2b6@coco.lan>
In-Reply-To: <20210525053359.1147899-1-mudongliangabcd@gmail.com>
References: <20210525053359.1147899-1-mudongliangabcd@gmail.com>
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Em Tue, 25 May 2021 13:33:59 +0800
Dongliang Mu <mudongliangabcd@gmail.com> escreveu:

> When cinergyt2_frontend_attach returns a negative value, the allocation
> is already successful, but in the error handling, there is no any clean
> corresponding operation, which leads to memory leak.
> 
> Fix it by freeing struct cinergyt2_fe_state when the return value is
> nonzero.
> 
> backtrace:
>   [<0000000056e17b1a>] kmalloc include/linux/slab.h:552 [inline]
>   [<0000000056e17b1a>] kzalloc include/linux/slab.h:682 [inline]
>   [<0000000056e17b1a>] cinergyt2_fe_attach+0x21/0x80 drivers/media/usb/dvb-usb/cinergyT2-fe.c:271
>   [<00000000ae0b1711>] cinergyt2_frontend_attach+0x21/0x70 drivers/media/usb/dvb-usb/cinergyT2-core.c:74
>   [<00000000d0254861>] dvb_usb_adapter_frontend_init+0x11b/0x1b0 drivers/media/usb/dvb-usb/dvb-usb-dvb.c:290
>   [<0000000002e08ac6>] dvb_usb_adapter_init drivers/media/usb/dvb-usb/dvb-usb-init.c:84 [inline]
>   [<0000000002e08ac6>] dvb_usb_init drivers/media/usb/dvb-usb/dvb-usb-init.c:173 [inline]
>   [<0000000002e08ac6>] dvb_usb_device_init.cold+0x4d0/0x6ae drivers/media/usb/dvb-usb/dvb-usb-init.c:287
> 
> Reported-by: syzbot+e1de8986786b3722050e@syzkaller.appspotmail.com
> Signed-off-by: Dongliang Mu <mudongliangabcd@gmail.com>
> ---
>  drivers/media/usb/dvb-usb/dvb-usb-dvb.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/media/usb/dvb-usb/dvb-usb-dvb.c b/drivers/media/usb/dvb-usb/dvb-usb-dvb.c
> index 0a7f8ba90992..f9f004fb0a92 100644
> --- a/drivers/media/usb/dvb-usb/dvb-usb-dvb.c
> +++ b/drivers/media/usb/dvb-usb/dvb-usb-dvb.c
> @@ -288,7 +288,7 @@ int dvb_usb_adapter_frontend_init(struct dvb_usb_adapter *adap)
>  		}
>  
>  		ret = adap->props.fe[i].frontend_attach(adap);
> -		if (ret || adap->fe_adap[i].fe == NULL) {
> +		if (adap->fe_adap[i].fe == NULL) {
>  			/* only print error when there is no FE at all */
>  			if (i == 0)
>  				err("no frontend was attached by '%s'",
> @@ -297,6 +297,12 @@ int dvb_usb_adapter_frontend_init(struct dvb_usb_adapter *adap)
>  			return 0;
>  		}
>  
> +		if (ret) {
> +			struct dvb_frontend *fe = adap->fe_adap[i].fe;
> +
> +			fe->ops.release(fe);
> +			return 0;
> +		}
> +

Touching dvb-usb core doesn't seem the right fix here, as it will
affect all other drivers that depend on it.

Basically, when a driver returns an error, it has to cleanup
whatever it did, as the core has no way to know where the
error happened inside the driver logic.

The problem seems to be at cinergyt2_frontend_attach() instead:

	adap->fe_adap[0].fe = cinergyt2_fe_attach(adap->dev);

        mutex_lock(&d->data_mutex);
        st->data[0] = CINERGYT2_EP1_GET_FIRMWARE_VERSION;

        ret = dvb_usb_generic_rw(d, st->data, 1, st->data, 3, 0);
        if (ret < 0) {
                deb_rc("cinergyt2_power_ctrl() Failed to retrieve sleep state info\n");
        }
        mutex_unlock(&d->data_mutex);

        /* Copy this pointer as we are gonna need it in the release phase */
        cinergyt2_usb_device = adap->dev;

        return ret;

See, this driver returns an error if it fails to talk with the hardware
when it calls dvb_usb_generic_rw(). Yet, it doesn't cleanup its own mess,
as it keeps the frontend attached. The right fix would be to call 
cinergyt2_fe_release() if ret < 0.

E. g., the above code should be, instead:

	if (ret < 0) {
		fe->ops.release(adap->fe_adap[0].fe);
                deb_rc("cinergyt2_power_ctrl() Failed to retrieve sleep state info\n");
        }

Thanks,
Mauro