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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4b4532916f2sm167407535e9.5.2026.11.05.12.53.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 05 Nov 2026 12:53:22 -0800 (PST) Date: Thu, 5 Nov 2026 20:53:21 +0000 From: David Laight To: Alejandro Colomar Cc: Mariia Nikitash , dmitry.torokhov@gmail.com, linux-input@vger.kernel.org, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org, kees@kernel.org, justinstitt@google.com, morbo@google.com Subject: Re: [PATCH] Input: mouse: vsxxxaa: Replace strlcat() with strscpy() Message-ID: <20261105205321.7b303231@pumpkin> In-Reply-To: References: <20261104062319.288360-1-nikitash.mariiaw@gmail.com> <20261105112813.13210334@pumpkin> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) X-Mailing-List: linux-hardening@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Thu, 5 Nov 2026 12:49:59 +0100 Alejandro Colomar wrote: > > Personally I think that while there are issues with strlcat() > > (mostly to do with its return value), and that there are often > > much better (and faster - so sprintf is out) ways of getting > > the same result, the deprecation really needs to propose a > > sensible alternative (not inlined strlen() + strscpy()). > > One alternative would be to add strscat(), with the obvious internal > strlen(3). This would be a drop-in replacement, and wouldn't have the > issues of strlcat(3) --mainly, the DoS vulnerability which is > consequence of the return value, and also the more difficult error > handling of doing '>=sizeof(...)' than '<0'--. I've had thoughts of a more general function - but I've not tried to write it. int str_append(char *dest, size_t dest_sz, size_t dest_off, const char *src, size_t src_max_len); Where dest_sz is usually sizeof(*dest) and the header can substitute that for a constant zero. dest_off would similarly default to strlen(dest), if -ve the function would return that value immediately. src_max_len would be used for an effective strnlen(src, src_max_len). The idea would be that calls like: char tgt[100]; len = str_append(tgt, 0, strscpy(tgt, src_1), src_2, 0); would append src_1 and src_2 in tgt returning -ve on overflow. (Further chaining would then work.) But, as I said, I've not tried to write it or see what it would look like in use. David