Re: [RFC/PATCH for 4.4.y] usb: gadget: configfs: Fix use-after-free issue with udc_name

[Greg KH <gregkh@linuxfoundation.org>]

On Mon, Dec 27, 2021 at 01:47:35PM +0100, Greg KH wrote:
> On Thu, Dec 23, 2021 at 02:26:26PM +0900, Nobuhiro Iwamatsu wrote:
> > From: Eddie Hung <eddie.hung@mediatek.com>
> > 
> > commit 64e6bbfff52db4bf6785fab9cffab850b2de6870 upstream.
> > 
> > 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.
> > 
> > Context 1:
> > gadget_dev_desc_UDC_store()->unregister_gadget()->
> > free udc_name->set udc_name to NULL
> > 
> > Context 2:
> > gadget_dev_desc_UDC_show()-> access udc_name
> > 
> > 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
> > 
> > Add mutex_lock to protect this kind of scenario.
> > 
> > Signed-off-by: Eddie Hung <eddie.hung@mediatek.com>
> > Signed-off-by: Macpaul Lin <macpaul.lin@mediatek.com>
> > Reviewed-by: Peter Chen <peter.chen@nxp.com>
> > Cc: stable@vger.kernel.org
> > Link: https://lore.kernel.org/r/1609239215-21819-1-git-send-email-macpaul.lin@mediatek.com
> > Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > [Reference: CVE-2021-39648]
> > [iwamatsu: struct usb_gadget_driver does not have udc_name variable.
> >            Change struct gadget_info's udc_name.]
> > Signed-off-by: Nobuhiro Iwamatsu (CIP) <nobuhiro1.iwamatsu@toshiba.co.jp>
> > ---
> >  drivers/usb/gadget/configfs.c | 11 ++++++++++-
> >  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> Now queued up, thanks.
> 
> greg k-h

Oops, nope, this gives me a build warning, something is wrong with this
change:

  CC [M]  drivers/usb/gadget/configfs.o
drivers/usb/gadget/configfs.c: In function ‘gadget_dev_desc_UDC_show’:
drivers/usb/gadget/configfs.c:249:18: warning: assignment discards ‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers]
  249 |         udc_name = gi->udc_name;
      |                  ^

Please always test-build your patches :(

thanks,

greg k-h