linux-hardening - [PATCH] serial: 8250_pci: Prefer struct

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Date:   Sun,  5 Sep 2021 17:57:28 +0200
From:   Len Baker <len.baker@....com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>
Cc:     Len Baker <len.baker@....com>, Kees Cook <keescook@...omium.org>,
        "Maciej W. Rozycki" <macro@...am.me.uk>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Mario Kleiner <mario.kleiner.de@...il.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Randy Wright <rwright@....com>,
        Christian Gmeiner <christian.gmeiner@...il.com>,
        Tobias Diedrich <tobiasdiedrich@...il.com>,
        YueHaibing <yuehaibing@...wei.com>, linux-serial@...r.kernel.org,
        linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] serial: 8250_pci: Prefer struct_size over open coded arithmetic

As noted in the "Deprecated Interfaces, Language Features, Attributes,
and Conventions" documentation [1], size calculations (especially
multiplication) should not be performed in memory allocator (or similar)
function arguments due to the risk of them overflowing. This could lead
to values wrapping around and a smaller allocation being made than the
caller was expecting. Using those allocations could lead to linear
overflows of heap memory and other misbehaviors.

So, use the struct_size() helper to do the arithmetic instead of the
argument "size + size * count" in the kzalloc() function.

[1] https://www.kernel.org/doc/html/v5.14/process/deprecated.html#open-coded-arithmetic-in-allocator-arguments

Signed-off-by: Len Baker <len.baker@....com>
---
 drivers/tty/serial/8250/8250_pci.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_pci.c b/drivers/tty/serial/8250/8250_pci.c
index a808c283883e..b97ade35d4a3 100644
--- a/drivers/tty/serial/8250/8250_pci.c
+++ b/drivers/tty/serial/8250/8250_pci.c
@@ -3981,9 +3981,7 @@ pciserial_init_ports(struct pci_dev *dev, const struct pciserial_board *board)
 			nr_ports = rc;
 	}

-	priv = kzalloc(sizeof(struct serial_private) +
-		       sizeof(unsigned int) * nr_ports,
-		       GFP_KERNEL);
+	priv = kzalloc(struct_size(priv, line, nr_ports), GFP_KERNEL);
 	if (!priv) {
 		priv = ERR_PTR(-ENOMEM);
 		goto err_deinit;
--
2.25.1