From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 898DDCA5FCE for ; Sun, 4 Oct 2026 07:26:46 +0000 (UTC) Received: from boromir.ozlabs.org (localhost [127.0.0.1]) by lists.ozlabs.org (Postfix) with ESMTP id 4hyDbm3dKBz2yr0; Sun, 04 Oct 2026 18:26:44 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; arc=none smtp.remote-ip=172.234.252.31 ARC-Seal: i=1; a=rsa-sha256; d=lists.ozlabs.org; s=201707; t=1791098804; cv=none; b=mNtVf23LH3SdDGZbmV3HdShhtjQ2CvjjIuokdk87u8Ap0dsSya+2CCtFS/aGa8b19GpJuu1dEKrPCM7JHVHNQDwxpA5tBfXT96ZRpzAzV6jHNog2/1DTeJ/Ybf+VQAr0iOhsfi9EXQe3VdmeXDZb+fN3F/PT8NHdyGwkn6qVLzVSTljpVdEUMzpRXuKcl2RYh0YWl5ikyw2sJFO7T+vFxW8PrYetrWaTpOkrSMdLXlQnpWGoeW45+013uN+sFz9jvTsTOmjAi7uhNlRZ5aQccg3+6Xb1YUqxnZ5XmKjrNUxx9bVewiwmIJ+vmJj/Nyb+h8QekWR3OrVGkL8RBTInFg== ARC-Message-Signature: i=1; a=rsa-sha256; d=lists.ozlabs.org; s=201707; t=1791098804; c=relaxed/relaxed; bh=cgIqnoufaHq6AdaBd0wZxGfVHkwrfWk/BsoFED6yW28=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=JBygIqIsx/yQoNbj1JgzOSOjMLEgki3xyh+L0Ihw8WCV+TmOv3g13XsR8Llbv+ipKJNE87B+Hm/cN24n1/DFalz6LZp4uIf9m7WjXLfhAkjzlv0nzQU8eMmK6Zf0uHdfJVIVxIWPyJ0W5U6vATEYIkoeFnZ8m4NPL7p7r2ZC/yIPr7O3zEQ8bZ3VabT5iwDUE2sc1Z+814QE/C9uhPfOW72QKU/2XK2Wmfev92HafTUEq4Vb9hxIi1+QPEIL/IOstD4BPdoQ0Cd7NtATKVbvhbpJ7q3tPNMTG1JWIw4GkCdcAkvQ6Ao+54W7TkPtiRbLxg4W2PU+Uaa5kPmm03bqGA== ARC-Authentication-Results: i=1; lists.ozlabs.org; dmarc=pass (p=quarantine dis=none) header.from=kernel.org; dkim=pass (2048-bit key; unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=nU5ReT3j; dkim-atps=neutral; spf=pass (client-ip=172.234.252.31; helo=sea.source.kernel.org; envelope-from=kees@kernel.org; receiver=lists.ozlabs.org) smtp.mailfrom=kernel.org Authentication-Results: lists.ozlabs.org; dmarc=pass (p=quarantine dis=none) header.from=kernel.org Authentication-Results: lists.ozlabs.org; dkim=pass (2048-bit key; unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=nU5ReT3j; dkim-atps=neutral Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=kernel.org (client-ip=172.234.252.31; helo=sea.source.kernel.org; envelope-from=kees@kernel.org; receiver=lists.ozlabs.org) Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange x25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4hyDbk51Jgz2yf9 for ; Sun, 04 Oct 2026 18:26:42 +1100 (AEDT) Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 9DA09413CA; Sun, 4 Oct 2026 07:26:39 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 761B31F000FF; Sun, 4 Oct 2026 07:26:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1791098799; bh=cgIqnoufaHq6AdaBd0wZxGfVHkwrfWk/BsoFED6yW28=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=nU5ReT3jHCTKrC3vFlt6lFhBY2qzd5TcweumZDdG4PoYUxRdUjykUFoBgFNWA1PjY T9Yu+RIKP64tp84D9IUIBtDjfeFi3o967G8MkqSZgLs5zg6QgwCaZo2Pxoykxskztl biV5O05MJfDy50y8GDgflF67Yd7yP+x3fcZ/CTySFwAWfFHWKch8vNf6E6pnkc8Req OzpDMqE/uOHVQp8wJMzmgk75NkJ+Q6sBYYfXWMn9gwMNio09Jz0A1FkvjaPxByIoTx USuuhCbzR7WCiikqNFCVjzo7VO44aK7kcE+i2spiWR4WgjRoXKk74e4z7OK8rvjehn Jk/eIKWbHt2nQ== Date: Sun, 4 Oct 2026 00:26:39 -0700 From: Kees Cook To: Andy Shevchenko Cc: Bill Wendling , "Matthew Wilcox (Oracle)" , Andrew Morton , David Gow , Petr Mladek , Shuvam Pandey , Steven Rostedt , Jonathan Corbet , Sergey Senozhatsky , =?iso-8859-1?Q?G=FCnther?= Noack , =?iso-8859-1?Q?Micka=EBl_Sala=FCn?= , Masami Hiramatsu , Mathieu Desnoyers , Jiri Kosina , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Eduard Zingerman , Kumar Kartikeya Dwivedi , Martin KaFai Lau , Song Liu , Yonghong Song , Jiri Olsa , Emil Tsalapatis , Ihor Solodrai , "Christophe Leroy (CS GROUP)" , Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= , Madhavan Srinivasan , Michael Ellerman , Nicholas Piggin , Shivaprasad G Bhat , Thorsten Blum , Alison Schofield , Dave Jiang , Greg Kroah-Hartman , Guangshuo Li , Ira Weiny , Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= , Vishal Verma , Randy Dunlap , Shuah Khan , linux-kernel@vger.kernel.org, bpf@vger.kernel.org, linux-security-module@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, nvdimm@lists.linux.dev, linux-doc@vger.kernel.org, linux-hardening@vger.kernel.org Subject: Re: [PATCH v4 05/11] seq_buf: Add seq_buf_strlen() Message-ID: <202610040023.A3865A6@keescook> References: <20261003035906.too.263-kees@kernel.org> <20261003035921.1918874-5-kees@kernel.org> X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Sat, Oct 03, 2026 at 06:36:49PM +0300, Andy Shevchenko wrote: > On Fri, Oct 02, 2026 at 08:59:10PM -0700, Kees Cook wrote: > > Several strlcat() call sites being converted to seq_buf need behavior > > seq_buf doesn't currently provide. The return from seq_buf_used() is > > not the length of the string in a seq_buf. Once the buffer is full or > > has overflowed it returns the buffer size, which counts the byte that > > seq_buf_str() replaces with the NUL, so a caller that needs the string > > and its length has to call seq_buf_str() and then walk the string with > > strlen(). > > > > Move the termination out of seq_buf_str() into a helper that returns > > where it put the NUL, and add seq_buf_strlen(), which terminates the > > buffer in the same way and returns that offset. > > > > As discussed in review, don't add WARN_ON() for seq_buf_strlen() and > > drop it from seq_buf_str(). > > > > Add tests comparing seq_buf_strlen() against strlen() of seq_buf_str() > > for empty, appended, truncated, exactly full, and overflowed buffers, > > checking that seq_buf_strlen() alone terminates a full buffer, and > > checking that a zero-sized seq_buf reports an empty string from both > > accessors without touching the buffer. > > > > Tests passed under qemu on ARCH=x86_64 with GCC 16.2.0 and CONFIG_KASAN=y, > > and on big-endian ARCH=s390 with GCC s390x-linux-gnu 16.2.0. > > ... > > > static inline const char *seq_buf_str(struct seq_buf *s) > > { > > - if (WARN_ON(s->size == 0)) > > + if (s->size == 0) > > return ""; > > > > - if (seq_buf_buffer_left(s)) > > - s->buffer[s->len] = 0; > > - else > > - s->buffer[s->size - 1] = 0; > > + __seq_buf_terminate(s); > > > > return s->buffer; > > } > > Looking at this again, can't it be rewritten now using _strlen()? > > if (seq_buf_strlen(s)) > return s->buffer; > > return ""; > > ? It could, but I'm vaguely nervous about the difference between s->buffer[0] == '\0' and .data "" i.e. we only force the return of seq_buf_str() to be _not_ just s->buffer when s->buffer is weirdly impossible (due to size == 0). I'd rather not make all 0-len strings return the .data segment's const "" string... -- Kees Cook