[PATCH AUTOSEL 5.6 125/606] USB: core: Fix misleading driver bug report

Sasha Levin
2020-06-09T00:34:12Z

From: Alan Stern <stern@rowland.harvard.edu>

[ Upstream commit ac854131d9844f79e2fdcef67a7707227538d78a ]

The syzbot fuzzer found a race between URB submission to endpoint 0
and device reset. Namely, during the reset we call usb_ep0_reinit()
because the characteristics of ep0 may have changed (if the reset
follows a firmware update, for example). While usb_ep0_reinit() is
running there is a brief period during which the pointers stored in
udev->ep_in[0] and udev->ep_out[0] are set to NULL, and if an URB is
submitted to ep0 during that period, usb_urb_ep_type_check() will
report it as a driver bug. In the absence of those pointers, the
routine thinks that the endpoint doesn't exist. The log message looks
like this:

------------[ cut here ]------------
usb 2-1: BOGUS urb xfer, pipe 2 != type 2
WARNING: CPU: 0 PID: 9241 at drivers/usb/core/urb.c:478
usb_submit_urb+0x1188/0x1460 drivers/usb/core/urb.c:478

Now, although submitting an URB while the device is being reset is a
questionable thing to do, it shouldn't count as a driver bug as severe
as submitting an URB for an endpoint that doesn't exist. Indeed,
endpoint 0 always exists, even while the device is in its unconfigured
state.

To prevent these misleading driver bug reports, this patch updates
usb_disable_endpoint() to avoid clearing the ep_in[] and ep_out[]
pointers when the endpoint being disabled is ep0. There's no danger
of leaving a stale pointer in place, because the usb_host_endpoint
structure being pointed to is stored permanently in udev->ep0; it
doesn't get deallocated until the entire usb_device structure does.

Reported-and-tested-by: syzbot+db339689b2101f6f6071@syzkaller.appspotmail.com
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>

Link: https://lore.kernel.org/r/Pine.LNX.4.44L0.2005011558590.903-100000@netrider.rowland.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/usb/core/message.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/core/message.c b/drivers/usb/core/message.c
index 02eaac7e1e34..a1ac2f0723b0 100644
--- a/drivers/usb/core/message.c
+++ b/drivers/usb/core/message.c
@@ -1143,11 +1143,11 @@ void usb_disable_endpoint(struct usb_device *dev, unsigned int epaddr,

if (usb_endpoint_out(epaddr)) {
ep = dev->ep_out[epnum];
- if (reset_hardware)
+ if (reset_hardware && epnum != 0)
dev->ep_out[epnum] = NULL;
} else {
ep = dev->ep_in[epnum];
- if (reset_hardware)
+ if (reset_hardware && epnum != 0)
dev->ep_in[epnum] = NULL;
}
if (ep) {
--
2.25.1