linux-kernel - Re: [PATCH][next] clk: imx: pll14xx: Fix potential integer overflow on multiplication

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <3e0def9f-ebb6-4171-9395-1da118b0ea29@stanley.mountain>
Date: Mon, 7 Oct 2024 12:54:43 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Colin Ian King <colin.i.king@...il.com>
Cc: Abel Vesa <abelvesa@...nel.org>, Peng Fan <peng.fan@....com>,
	Michael Turquette <mturquette@...libre.com>,
	Stephen Boyd <sboyd@...nel.org>, Shawn Guo <shawnguo@...nel.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Pengutronix Kernel Team <kernel@...gutronix.de>,
	Fabio Estevam <festevam@...il.com>, linux-clk@...r.kernel.org,
	imx@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
	kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][next] clk: imx: pll14xx: Fix potential integer overflow
 on multiplication

On Mon, Oct 07, 2024 at 09:48:40AM +0100, Colin Ian King wrote:
> The calculation of fout is using int multiplication and assigning
> the result to a u64, this can potentially overflow if the int variable
> mdiv is too large. Fix this by making the 65536 a u64 value to ensure a
> u64 multiplication is being performed to avoid the overflow.
> 
> Fixes: 53990cf9d5b4 ("clk: imx: pll14xx: consolidate rate calculation")
> Signed-off-by: Colin Ian King <colin.i.king@...il.com>

mdiv is always clamped in then 0-1023 range by one of these:

	mdiv = FIELD_GET(MDIV_MASK, pll_div_ctl0);
	mdiv = clamp(mdiv, 64, 1023);

so it can't overflow and the Fixes tag is unnecessary.

I think the reason why "fout" is declared as a u64 is because we were worried
that on 32 bit systems the "fout *=" operation could overflow.  That looks
reasonable to me.

regards,
dan carpenter