linux-kernel - [PATCH 2/2] xhci: fix uninitialized string returned by xhci_decode_ctrl

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Date:   Tue, 22 Feb 2022 15:41:17 +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 2/2] xhci: fix uninitialized string returned by xhci_decode_ctrl_ctx()

xhci_decode_ctrl_ctx() returns the untouched buffer as-is if both "drop"
and "add" parameters are zero.

Fix the function to return an empty string in that case.

It was not immediately clear from the possible call chains whether this
issue is currently actually triggerable or not.

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: 90d6d5731da7 ("xhci: Add tracing for input control context")
Signed-off-by: Anssi Hannula <anssi.hannula@...wise.fi>
---
 drivers/usb/host/xhci.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/usb/host/xhci.h b/drivers/usb/host/xhci.h
index ac91647195f6..a2fcefb5a0bb 100644
--- a/drivers/usb/host/xhci.h
+++ b/drivers/usb/host/xhci.h
@@ -2465,6 +2465,8 @@ static inline const char *xhci_decode_ctrl_ctx(char *str,
 	unsigned int	bit;
 	int		ret = 0;

+	str[0] = '\0';
+
 	if (drop) {
 		ret = sprintf(str, "Drop:");
 		for_each_set_bit(bit, &drop, 32)
-- 
2.34.1