[PATCH] qmi_wwan: Fix out-of-bounds read

[Kristian Evensen <kristian.evensen@gmail.com>]

commit 904d88d743b0c94092c5117955eab695df8109e8 upstream.

The syzbot reported

 Call Trace:
  __dump_stack lib/dump_stack.c:77 [inline]
  dump_stack+0xca/0x13e lib/dump_stack.c:113
  print_address_description+0x67/0x231 mm/kasan/report.c:188
  __kasan_report.cold+0x1a/0x32 mm/kasan/report.c:317
  kasan_report+0xe/0x20 mm/kasan/common.c:614
  qmi_wwan_probe+0x342/0x360 drivers/net/usb/qmi_wwan.c:1417
  usb_probe_interface+0x305/0x7a0 drivers/usb/core/driver.c:361
  really_probe+0x281/0x660 drivers/base/dd.c:509
  driver_probe_device+0x104/0x210 drivers/base/dd.c:670
  __device_attach_driver+0x1c2/0x220 drivers/base/dd.c:777
  bus_for_each_drv+0x15c/0x1e0 drivers/base/bus.c:454

Caused by too many confusing indirections and casts.
id->driver_info is a pointer stored in a long.  We want the
pointer here, not the address of it.

Thanks-to: Hillf Danton <hdanton@sina.com>
Reported-by: syzbot+b68605d7fadd21510de1@syzkaller.appspotmail.com
Cc: Kristian Evensen <kristian.evensen@gmail.com>
Fixes: e4bf63482c30 ("qmi_wwan: Add quirk for Quectel dynamic config")
Signed-off-by: Bjørn Mork <bjorn@mork.no>

[Upstream commit did not apply because I shuffled two lines in the
backport. The fixes tag for 4.14 is 3a6a5107ceb3.]

Signed-off-by: Kristian Evensen <kristian.evensen@gmail.com>
---
 drivers/net/usb/qmi_wwan.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/usb/qmi_wwan.c b/drivers/net/usb/qmi_wwan.c
index c2d6c501d..063daa343 100644
--- a/drivers/net/usb/qmi_wwan.c
+++ b/drivers/net/usb/qmi_wwan.c
@@ -1395,14 +1395,14 @@ static int qmi_wwan_probe(struct usb_interface *intf,
 		return -ENODEV;
 	}
 
-	info = (void *)&id->driver_info;
-
 	/* Several Quectel modems supports dynamic interface configuration, so
 	 * we need to match on class/subclass/protocol. These values are
 	 * identical for the diagnostic- and QMI-interface, but bNumEndpoints is
 	 * different. Ignore the current interface if the number of endpoints
 	 * equals the number for the diag interface (two).
 	 */
+	info = (void *)id->driver_info;
+
 	if (info->data & QMI_WWAN_QUIRK_QUECTEL_DYNCFG) {
 		if (desc->bNumEndpoints == 2)
 			return -ENODEV;
-- 
2.20.1