linux-kernel - Re: [PATCH] drivers/fsi/scom: Return -EFAULT if copy fails

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Message-ID: <413f4e50-b722-427f-ab30-d320efe71cc0@kili.mountain>
Date:   Tue, 23 May 2023 10:05:45 +0300
From:   Dan Carpenter <dan.carpenter@...aro.org>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Su Hui <suhui@...china.com>, Jeremy Kerr <jk@...abs.org>,
        Joel Stanley <joel@....id.au>,
        Alistar Popple <alistair@...ple.id.au>,
        Eddie James <eajames@...ux.ibm.com>, eajames@...ibm.com,
        kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org,
        cbostic@...ux.vnet.ibm.com, linux-fsi@...ts.ozlabs.org
Subject: Re: [PATCH] drivers/fsi/scom: Return -EFAULT if copy fails

On Mon, May 22, 2023 at 03:30:06PM -0700, Guenter Roeck wrote:
> On Fri, May 19, 2023 at 09:37:10AM +0800, Su Hui wrote:
> > The copy_to/from_user() functions return the number of bytes remaining
> > to be copied, but we want to return -EFAULT to the user.
> > 
> Why ? EFAULT means that a bad address was provided, and it is not
> immediately obvious why that would be the case.
> 

Right now the function is returning success so that's definitely wrong.
The copy_to/from_user() function will only fail if a bad address is
provided so -EFAULT is correct.

There is a different Smatch warning for when people return a different
error code such as -EINVAL.
drivers/fsi/fsi-scom.c:337 scom_read() warn: return -EFAULT instead of '-EINVAL'
The return affects the user and -EFAULT but that level of pendantry feel
like possibly too much?  There aren't many instances of this warning.

regards,
dan carpenter