linux-kernel - [PATCH 1/2] xhci: fix garbage USBSTS being logged in some cases

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Date:   Tue, 22 Feb 2022 15:41:16 +0200
From:   Anssi Hannula <anssi.hannula@...wise.fi>
To:     Mathias Nyman <mathias.nyman@...el.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] xhci: fix garbage USBSTS being logged in some cases

xhci_decode_usbsts() is expected to return a zero-terminated string by
its only caller, xhci_stop_endpoint_command_watchdog(), which directly
logs the return value:

  xhci_warn(xhci, "USBSTS:%s\n", xhci_decode_usbsts(str, usbsts));

However, if no recognized bits are set in usbsts, the function will
return without having called any sprintf() and therefore return an
untouched non-zero-terminated caller-provided buffer, causing garbage
to be output to log.

Fix that by always including the raw value in the output.

Note that before 4843b4b5ec64 ("xhci: fix even more unsafe memory usage
in xhci tracing") the result effect in the failure case was different as
a static buffer was used here, but the code still worked incorrectly.

Fixes: 9c1aa36efdae ("xhci: Show host status when watchdog triggers and host is assumed dead.")
Signed-off-by: Anssi Hannula <anssi.hannula@...wise.fi>
---

Noticed this while debugging a USB issue. Let me know if you prefer a
different fix.

 drivers/usb/host/xhci.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/usb/host/xhci.h b/drivers/usb/host/xhci.h
index 8a0026ee9524..ac91647195f6 100644
--- a/drivers/usb/host/xhci.h
+++ b/drivers/usb/host/xhci.h
@@ -2642,6 +2642,7 @@ static inline const char *xhci_decode_usbsts(char *str, u32 usbsts)
 		ret += sprintf(str + ret, " CNR");
 	if (usbsts & STS_HCE)
 		ret += sprintf(str + ret, " HCE");
+	ret += sprintf(str + ret, " (0x%08x)", usbsts);

 	return str;
 }
-- 
2.34.1