linux-kernel - Re: [Cocci] [PATCH] usb: atm: don't use snprintf() for sysfs attrs

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Message-ID: <alpine.DEB.2.22.394.2008272334500.2482@hadrien>
Date:   Thu, 27 Aug 2020 23:36:28 +0200 (CEST)
From:   Julia Lawall <julia.lawall@...ia.fr>
To:     Denis Efremov <efremov@...ux.com>
cc:     Julia Lawall <julia.lawall@...ia.fr>,
        Joe Perches <joe@...ches.com>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        linux-kernel@...r.kernel.org, cocci <cocci@...teme.lip6.fr>,
        accessrunner-general@...ts.sourceforge.net,
        Alex Dewar <alex.dewar90@...il.com>
Subject: Re: [Cocci] [PATCH] usb: atm: don't use snprintf() for sysfs attrs



On Fri, 28 Aug 2020, Denis Efremov wrote:

> Hi all,
>
> On 8/27/20 10:42 PM, Julia Lawall wrote:
> >
> >
> > On Thu, 27 Aug 2020, Joe Perches wrote:
> >
> >> On Thu, 2020-08-27 at 15:48 +0100, Alex Dewar wrote:
> >>> On Thu, Aug 27, 2020 at 03:41:06PM +0200, Rasmus Villemoes wrote:
> >>>> On 27/08/2020 15.18, Alex Dewar wrote:
> >>>>> On Thu, Aug 27, 2020 at 09:15:37AM +0200, Greg Kroah-Hartman wrote:
> >>>>>> On Thu, Aug 27, 2020 at 08:42:06AM +0200, Rasmus Villemoes wrote:
> >>>>>>> On 25/08/2020 00.23, Alex Dewar wrote:
> >>>>>>>> kernel/cpu.c: don't use snprintf() for sysfs attrs
> >>>>>>>>
> >>>>>>>> As per the documentation (Documentation/filesystems/sysfs.rst),
> >>>>>>>> snprintf() should not be used for formatting values returned by sysfs.
>
> Just FYI, I've send an addition to the device_attr_show.cocci script[1] to turn
> simple cases of snprintf (e.g. "%i") to sprintf. Looks like many developers would
> like it more than changing snprintf to scnprintf. As for me, I don't like the idea
> of automated altering of the original logic from bounded snprint to unbouded one
> with sprintf.
>
> [1] https://lkml.org/lkml/2020/8/13/786
>
> Regarding current device_attr_show.cocci implementation, it detects the functions
> by declaration:
> ssize_t any_name(struct device *dev, struct device_attribute *attr, char *buf)
>
> and I limited the check to:
> "return snprintf"
> pattern because there are already too many warnings.
>
> Actually, it looks more correct to check for:
> ssize_t show(struct device *dev, struct device_attribute *attr, char *buf)
> {
>         <...
> *       snprintf@p(...);
>         ...>
> }
>
> This pattern should also highlight the snprintf calls there we save returned
> value in a var, e.g.:
>
> ret += snprintf(...);
> ...
> ret += snprintf(...);
> ...
> ret += snprintf(...);
>
> return ret;
>
> >
> > Something like
> >
> > identifier f;
> > fresh identifier = "sysfs" ## f;
> >
> > may be useful.  Let me know if further help is needed.
>
> Initially, I wrote the rule to search for DEVICE_ATTR(..., ..., func_name, ...)

This is what I would have expected.

> functions. However, it looks like matching function prototype is enough. At least,
> I failed to find false positives. I rejected the initial DEVICE_ATTR() searching
> because I thought that it's impossible to handle DEVICE_ATTR_RO()/DEVICE_ATTR_RW()
> macroses with coccinelle as they "generate" function names internally with
> "##". "fresh identifier" should really help here, but now I doubt it's required in
> device_attr_show.cocci, function prototype is enough.

It's true that it is probably unique enough.

julia