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From:   Peter Chen <peter.chen@nxp.com>
To:     Macpaul Lin <macpaul.lin@mediatek.com>
CC:     Felipe Balbi <balbi@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        "linux-usb@vger.kernel.org" <linux-usb@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
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        <linux-mediatek@lists.infradead.org>,
        Mediatek WSD Upstream <wsd_upstream@mediatek.com>,
        Macpaul Lin <macpaul.lin@gmail.com>,
        Eddie Hung <eddie.hung@mediatek.com>,
        "stable@vger.kernel.org" <stable@vger.kernel.org>
Subject: Re: [PATCH] usb: gadget: configfs: Fix use-after-free issue with
 udc_name
Thread-Topic: [PATCH] usb: gadget: configfs: Fix use-after-free issue with
 udc_name
Thread-Index: AQHWWzwrDCeJbXR+QUOUa8VdThQTA6kLKvMA
Date:   Fri, 17 Jul 2020 04:14:08 +0000
Message-ID: <20200717041406.GC17070@b29397-desktop>
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On 20-07-16 14:41:06, Macpaul Lin wrote:
> There is a use-after-free issue, if access udc_name
> in function gadget_dev_desc_UDC_store after another context
> free udc_name in function unregister_gadget.
>=20
> Contex 1:

%s/contex/context

> gadget_dev_desc_UDC_store()->unregister_gadget()->
> free udc_name->set udc_name to NULL
>=20
> Contex 2:

The same, otherwise:

Reviewed-by: Peter Chen <peter.chen@nxp.com>

Peter

> gadget_dev_desc_UDC_show()-> access udc_name
>=20
> Call trace:
> dump_backtrace+0x0/0x340
> show_stack+0x14/0x1c
> dump_stack+0xe4/0x134
> print_address_description+0x78/0x478
> __kasan_report+0x270/0x2ec
> kasan_report+0x10/0x18
> __asan_report_load1_noabort+0x18/0x20
> string+0xf4/0x138
> vsnprintf+0x428/0x14d0
> sprintf+0xe4/0x12c
> gadget_dev_desc_UDC_show+0x54/0x64
> configfs_read_file+0x210/0x3a0
> __vfs_read+0xf0/0x49c
> vfs_read+0x130/0x2b4
> SyS_read+0x114/0x208
> el0_svc_naked+0x34/0x38
>=20
> Add mutex_lock to protect this kind of scenario.

>=20
> Signed-off-by: Eddie Hung <eddie.hung@mediatek.com>
> Signed-off-by: Macpaul Lin <macpaul.lin@mediatek.com>
> Cc: stable@vger.kernel.org
> ---
>  drivers/usb/gadget/configfs.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
>=20
> diff --git a/drivers/usb/gadget/configfs.c b/drivers/usb/gadget/configfs.=
c
> index 9dc06a4e1b30..21110b2865b9 100644
> --- a/drivers/usb/gadget/configfs.c
> +++ b/drivers/usb/gadget/configfs.c
> @@ -221,9 +221,16 @@ static ssize_t gadget_dev_desc_bcdUSB_store(struct c=
onfig_item *item,
> =20
>  static ssize_t gadget_dev_desc_UDC_show(struct config_item *item, char *=
page)
>  {
> -	char *udc_name =3D to_gadget_info(item)->composite.gadget_driver.udc_na=
me;
> +	struct gadget_info *gi =3D to_gadget_info(item);
> +	char *udc_name;
> +	int ret;
> +
> +	mutex_lock(&gi->lock);
> +	udc_name =3D gi->composite.gadget_driver.udc_name;
> +	ret =3D sprintf(page, "%s\n", udc_name ?: "");
> +	mutex_unlock(&gi->lock);
> =20
> -	return sprintf(page, "%s\n", udc_name ?: "");
> +	return ret;
>  }
> =20
>  static int unregister_gadget(struct gadget_info *gi)
> --=20
> 2.18.0

--=20

Thanks,
Peter Chen=