[Trusty][CVE-2017-100363][PATCH] char: lp: fix possible integer overflow in lp_setup()

[Po-Hsu Lin]

From: Willy Tarreau <w at 1wt.eu>

CVE-2017-100363

The lp_setup() code doesn't apply any bounds checking when passing
"lp=none", and only in this case, resulting in an overflow of the
parport_nr[] array. All versions in Git history are affected.

Reported-By: Roee Hay <roee.hay at hcl.com>
Cc: Ben Hutchings <ben at decadent.org.uk>
Cc: stable at vger.kernel.org
Signed-off-by: Willy Tarreau <w at 1wt.eu>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
(cherry picked from commit 3e21f4af170bebf47c187c1ff8bf155583c9f3b1)

Signed-off-by: Po-Hsu Lin <po-hsu.lin at canonical.com>
---
 drivers/char/lp.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/char/lp.c b/drivers/char/lp.c
index 0913d79..6b61910 100644
--- a/drivers/char/lp.c
+++ b/drivers/char/lp.c
@@ -857,7 +857,11 @@ static int __init lp_setup (char *str)
 	} else if (!strcmp(str, "auto")) {
 		parport_nr[0] = LP_PARPORT_AUTO;
 	} else if (!strcmp(str, "none")) {
-		parport_nr[parport_ptr++] = LP_PARPORT_NONE;
+		if (parport_ptr < LP_NO)
+			parport_nr[parport_ptr++] = LP_PARPORT_NONE;
+		else
+			printk(KERN_INFO "lp: too many ports, %s ignored.\n",
+			       str);
 	} else if (!strcmp(str, "reset")) {
 		reset = 1;
 	}
-- 
1.7.9.5