usb: early: xhci-dbc: Fix a potential out-of-bound memory access

[ Upstream commit a4a97ab3db5c081eb6e7dba91306adefb461e0bd ]

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@wanadoo.fr>
Link: https://lore.kernel.org/r/d6a7562c5e839a195cee85db6dc81817f9372cb1.1675016180.git.christophe.jaillet@wanadoo.fr
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/usb/early/xhci-dbc.c b/drivers/usb/early/xhci-dbc.c
index bfb7e2b..7ef0a4b 100644 (file)
--- a/drivers/usb/early/xhci-dbc.c
+++ b/drivers/usb/early/xhci-dbc.c
@@ -874,7 +874,8 @@ retry:
 
 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;