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Subject: Re: [Cocci] [PATCH] usb: atm: don't use snprintf() for sysfs attrs
From:   Joe Perches <joe@perches.com>
To:     Julia Lawall <julia.lawall@inria.fr>,
        Denis Efremov <efremov@linux.com>
Cc:     "Gustavo A. R. Silva" <gustavoars@kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-usb@vger.kernel.org,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        linux-kernel@vger.kernel.org, cocci <cocci@systeme.lip6.fr>,
        accessrunner-general@lists.sourceforge.net,
        Alex Dewar <alex.dewar90@gmail.com>
Date:   Thu, 27 Aug 2020 14:44:01 -0700
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On Thu, 2020-08-27 at 23:36 +0200, Julia Lawall wrote:
> On Fri, 28 Aug 2020, Denis Efremov wrote:
[]
> 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.

I tried:
@@
identifier f_show =~ "^.*_show$";
identifier dev, attr, buf;
const char *chr;
@@
ssize_t f_show(struct device *dev, struct device_attribute *attr, char
*buf)
{
	<...
(
-	sprintf
+	sysfs_sprintf
	(...);
|
-	snprintf(buf, PAGE_SIZE,
+	sysfs_sprintf(buf,
	...);
|
-	scnprintf(buf, PAGE_SIZE,
+	sysfs_sprintf(buf,
	...);
|
	strcpy(buf, chr);
	sysfs_strcpy(buf, chr);
)
	...>
}

which finds direct statements without an assign
but that doesn't find

arch/arm/common/dmabounce.c:static ssize_t dmabounce_show(struct device *dev, struct device_attribute *attr, char *buf)
arch/arm/common/dmabounce.c-{
arch/arm/common/dmabounce.c-    struct dmabounce_device_info *device_info = dev->archdata.dmabounce;
arch/arm/common/dmabounce.c-    return sprintf(buf, "%lu %lu %lu %lu %lu %lu\n",
arch/arm/common/dmabounce.c-            device_info->small.allocs,
arch/arm/common/dmabounce.c-            device_info->large.allocs,
arch/arm/common/dmabounce.c-            device_info->total_allocs - device_info->small.allocs -
arch/arm/common/dmabounce.c-                    device_info->large.allocs,
arch/arm/common/dmabounce.c-            device_info->total_allocs,
arch/arm/common/dmabounce.c-            device_info->map_op_count,
arch/arm/common/dmabounce.c-            device_info->bounce_count);
arch/arm/common/dmabounce.c-}