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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id a13sm3327169pjq.36.2020.08.27.15.20.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 27 Aug 2020 15:20:55 -0700 (PDT) Date: Thu, 27 Aug 2020 15:20:54 -0700 From: Kees Cook To: Denis Efremov Cc: Julia Lawall , Joe Perches , "Gustavo A. R. Silva" , Greg Kroah-Hartman , linux-usb@vger.kernel.org, Rasmus Villemoes , linux-kernel@vger.kernel.org, cocci , accessrunner-general@lists.sourceforge.net, Alex Dewar Subject: Re: [Cocci] [PATCH] usb: atm: don't use snprintf() for sysfs attrs Message-ID: <202008271517.ECC1F1F8F@keescook> References: <20200824222322.22962-1-alex.dewar90@gmail.com> <48f2dc90-7852-eaf1-55d7-2c85cf954688@rasmusvillemoes.dk> <20200827071537.GA168593@kroah.com> <20200827131819.7rcl2f5js3hkoqj2@lenovo-laptop> <20200827144846.yauuttjaqtxaldxg@lenovo-laptop> <5d1dfb9b031130d4d20763ec621233a19d6a88a2.camel@perches.com> <5853c58e-7d26-2cf9-6cbf-698ecd93cbf9@linux.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5853c58e-7d26-2cf9-6cbf-698ecd93cbf9@linux.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Aug 28, 2020 at 12:01:34AM +0300, Denis Efremov wrote: > 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. 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 ...); return PAGE_SIZE - remaining; } -- Kees Cook