linux-kernel - [PATCH 1/1] misc: c2port: core: Make copying name from userspace more secure

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Message-Id: <20200714083259.1313267-1-lee.jones@linaro.org>
Date:   Tue, 14 Jul 2020 09:32:59 +0100
From:   Lee Jones <lee.jones@...aro.org>
To:     arnd@...db.de, gregkh@...uxfoundation.org
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Lee Jones <lee.jones@...aro.org>,
        Rodolfo Giometti <giometti@...eenne.com>,
        "Eurotech S.p.A" <info@...otech.it>,
        Geert Uytterhoeven <geert+renesas@...der.be>
Subject: [PATCH 1/1] misc: c2port: core: Make copying name from userspace more secure

Currently the 'c2dev' device data is not zeroed when its allocated.
Coupled with the fact strncpy() *may not* provide a NUL terminator
means that a 1-byte leak would be possible *if* this was ever copied
to userspace.

To prevent such a failing, let's first ensure the 'c2dev' device data
area is fully zeroed out and ensure the buffer will always be NUL
terminated by using the kernel's strscpy() which a) uses the
destination (instead of the source) size as the bytes to copy and b)
is *always* NUL terminated.

Cc: Rodolfo Giometti <giometti@...eenne.com>
Cc: "Eurotech S.p.A" <info@...otech.it>
Reported-by: Geert Uytterhoeven <geert+renesas@...der.be>
Signed-off-by: Lee Jones <lee.jones@...aro.org>
---
 drivers/misc/c2port/core.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/misc/c2port/core.c b/drivers/misc/c2port/core.c
index 80d87e8a0bea9..0de538a1cc1c6 100644
--- a/drivers/misc/c2port/core.c
+++ b/drivers/misc/c2port/core.c
@@ -899,7 +899,7 @@ struct c2port_device *c2port_device_register(char *name,
 		unlikely(!ops->c2d_get) || unlikely(!ops->c2d_set))
 		return ERR_PTR(-EINVAL);
 
-	c2dev = kmalloc(sizeof(struct c2port_device), GFP_KERNEL);
+	c2dev = kzalloc(sizeof(struct c2port_device), GFP_KERNEL);
 	if (unlikely(!c2dev))
 		return ERR_PTR(-ENOMEM);
 
@@ -923,7 +923,7 @@ struct c2port_device *c2port_device_register(char *name,
 	}
 	dev_set_drvdata(c2dev->dev, c2dev);
 
-	strncpy(c2dev->name, name, C2PORT_NAME_LEN - 1);
+	strscpy(c2dev->name, name, sizeof(c2dev->name));
 	c2dev->ops = ops;
 	mutex_init(&c2dev->mutex);
 
-- 
2.25.1