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

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Date:   Fri, 28 Aug 2020 07:39:25 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Kees Cook' <keescook@...omium.org>,
        Denis Efremov <efremov@...ux.com>
CC:     Julia Lawall <julia.lawall@...ia.fr>,
        Joe Perches <joe@...ches.com>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        cocci <cocci@...teme.lip6.fr>,
        "accessrunner-general@...ts.sourceforge.net" 
        <accessrunner-general@...ts.sourceforge.net>,
        Alex Dewar <alex.dewar90@...il.com>
Subject: RE: [Cocci] [PATCH] usb: atm: don't use snprintf() for sysfs attrs

From: Kees Cook
> Sent: 27 August 2020 23:21
...
> 
> Agreed. This just makes me cringe. If the API design declares that when
> a show() callback starts, buf has been allocated with PAGE_SIZE bytes,
> then that's how the logic should proceed, and it should be using
> scnprintf...
> 
> show(...) {
> 	size_t remaining = PAGE_SIZE;
> 
> 	...
> 	remaining -= scnprintf(buf, remaining, "fmt", var args ...);
> 	remaining -= scnprintf(buf, remaining, "fmt", var args ...);
> 	remaining -= scnprintf(buf, remaining, "fmt", var args ...);

Not quite what you had in mind, maybe:
	char *end = buf + PAGE_SIZE;

	buf += scnprintf(buf, end - buf, ...);

	return PAGE_SIZE - (end - buf);

	David

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