linux-kernel - [PATCH] tty: vt: keyboard: add range check to kbs->kb

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Message-Id: <20170920213828.5563-1-colin.king@canonical.com>
Date:   Wed, 20 Sep 2017 22:38:28 +0100
From:   Colin King <colin.king@...onical.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>, Ingo Molnar <mingo@...nel.org>
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] tty: vt: keyboard: add range check to kbs->kb_func index

From: Colin Ian King <colin.king@...onical.com>

A value outside the range 0..MAX_NR_FUNC-1 in kbs->kb_func will
cause an array bounds overflow on func_table. Fix this by adding
a range check.

Detected by CoverityScan, CID#401961 ("Untrusted array index read")

Fixes: 079c9534a96d ("vt:tackle kbd_table")
Signed-off-by: Colin Ian King <colin.king@...onical.com>
---
 drivers/tty/vt/keyboard.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/tty/vt/keyboard.c b/drivers/tty/vt/keyboard.c
index f4166263bb3a..1ecf545a96a8 100644
--- a/drivers/tty/vt/keyboard.c
+++ b/drivers/tty/vt/keyboard.c
@@ -1982,6 +1982,11 @@ int vt_do_kdgkb_ioctl(int cmd, struct kbsentry __user *user_kdgkb, int perm)
 	kbs->kb_string[sizeof(kbs->kb_string)-1] = '\0';
 	i = kbs->kb_func;
 
+	if (i < 0 || i >= MAX_NR_FUNC) {
+		ret = -EINVAL;
+		goto reterr;
+	}
+
 	switch (cmd) {
 	case KDGKBSENT:
 		sz = sizeof(kbs->kb_string) - 1; /* sz should have been
-- 
2.14.1