linux-kernel - Re: [PATCH] mei: bus: type promotion bug in mei_nfc_if

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Date:   Wed, 4 Jul 2018 13:59:14 +0200 (CEST)
From:   Julia Lawall <julia.lawall@...6.fr>
To:     Dan Carpenter <dan.carpenter@...cle.com>
cc:     Tomas Winkler <tomas.winkler@...el.com>,
        Alexander Usyskin <alexander.usyskin@...el.com>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] mei: bus: type promotion bug in mei_nfc_if_version()



On Wed, 4 Jul 2018, Dan Carpenter wrote:

> We accidentally removed the check for negative returns without
> considering the issue of type promotion.  The "if_version_length"
> variable is type size_t so if __mei_cl_recv() returns a negative then
> "bytes_recv" is type promoted to a high positive value and treated as
> success.
>
> Fixes: 582ab27a063a ("mei: bus: fix received data size check in NFC fixup")
> Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
>
> diff --git a/drivers/misc/mei/bus-fixup.c b/drivers/misc/mei/bus-fixup.c
> index 0208c4b027c5..fa0236a5e59a 100644
> --- a/drivers/misc/mei/bus-fixup.c
> +++ b/drivers/misc/mei/bus-fixup.c
> @@ -267,7 +267,7 @@ static int mei_nfc_if_version(struct mei_cl *cl,
>
>  	ret = 0;
>  	bytes_recv = __mei_cl_recv(cl, (u8 *)reply, if_version_length, 0);
> -	if (bytes_recv < if_version_length) {
> +	if (bytes_recv < 0 || bytes_recv < if_version_length) {

Is this preferred to adding an int cast?

julia

>  		dev_err(bus->dev, "Could not read IF version\n");
>  		ret = -EIO;
>  		goto err;
> --
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