linux-kernel - [PATCH 1/3] usb: early: xhci-dbc: Fix a potential out-of-bound memory access

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Message-Id: <d6a7562c5e839a195cee85db6dc81817f9372cb1.1675016180.git.christophe.jaillet@wanadoo.fr>
Date:   Sun, 29 Jan 2023 19:23:08 +0100
From:   Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     gregkh@...uxfoundation.org, peterz@...radead.org, pmladek@...e.com,
        john.ogness@...utronix.de, baolu.lu@...ux.intel.com,
        tglx@...utronix.de, mingo@...nel.org
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-janitors@...r.kernel.org,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>
Subject: [PATCH 1/3] usb: early: xhci-dbc: Fix a potential out-of-bound memory access

If xdbc_bulk_write() fails, the values in 'buf' can be anything. So the
string is not guaranteed to be NULL terminated when xdbc_trace() is called.

Reserve an extra byte, which will be zeroed automatically because 'buf' is
a static variable, in order to avoid troubles, should it happen.

Fixes: aeb9dd1de98c ("usb/early: Add driver for xhci debug capability")
Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
---
 drivers/usb/early/xhci-dbc.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/early/xhci-dbc.c b/drivers/usb/early/xhci-dbc.c
index 797047154820..f3e23be227d4 100644
--- a/drivers/usb/early/xhci-dbc.c
+++ b/drivers/usb/early/xhci-dbc.c
@@ -874,7 +874,8 @@ static int xdbc_bulk_write(const char *bytes, int size)
 
 static void early_xdbc_write(struct console *con, const char *str, u32 n)
 {
-	static char buf[XDBC_MAX_PACKET];
+	/* static variables are zeroed, so buf is always NULL terminated */
+	static char buf[XDBC_MAX_PACKET + 1];
 	int chunk, ret;
 	int use_cr = 0;
 
-- 
2.34.1