From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9B67C21CC51; Tue, 30 Jun 2026 22:58:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782860329; cv=none; b=HVfPa5ZfeS6oHubyBlQ760E5HSRTLUymde3WUOagDhCDrMTzBfugt9F/FDrKFCYtxLjELB905TMeL3j9qYByR+2SuDWiMvWx3cH3vRHyWSwwTFz3F+2vh59hfmFblb8uP0zRr0wFNI84QGQB/QBtSlD4HPeD5THnS8+Oms125yk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782860329; c=relaxed/simple; bh=aq9jJsGvYEawxXGAy0iuy6oK59s02bFHbdyTTS22zLs=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=OnS3jfucg5Exo/3vMgfbNkD15RU8e/F7PxQR4tLZZSWOMrzrtCpEtoG5d3uyxsU+OLdqZsUyjk/TSFuxzzzKbkHJCQpVhxm7D6lDAJSFgXJ8fZzLjEFGST/jj2eeQqGerseRbQDVFT4kRiQ2R7t4QEgP6T9RZMyUdbo/WIbl5rc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=P5f/0Kqj; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="P5f/0Kqj" Received: by smtp.kernel.org (Postfix) with ESMTPSA id EDD7A1F000E9; Tue, 30 Jun 2026 22:58:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1782860327; bh=LzgO/WtP3CHsUyiGKcx7YHKu/av/Fuaej/8zHHRDb7w=; h=Date:From:To:Cc:Subject:In-Reply-To:References; b=P5f/0Kqj6lvAulhzPauZEJUAACK0UeYeG67JPeOoa7qkcO1dP7Myuuhm4UNucWKW2 9wyUc/pJrFwZNZJK4e3fwBHIyN2qhib0otVdORx2OTuX8JypEzFW1zSdHGvaI+e3kG F0D9X3WwbFvOQwBCsqfAWFWi53X9n/FbXJQND2VazLnhy63w8RJB9CqUz+PmL0q2c3 Xsuj2OJn52BohKAcEmdS4AwsoicttbXsbDSbdnBo+tTB6zm879yreGjfM+nn3INXaF vVm/pKAas7BfW29vrOIlstDTbcSg2QmhyRtaxg/QthsnkKzETOb4VMGdzoPa+jbWiV SxcxGhczVzkkg== Date: Wed, 1 Jul 2026 07:58:43 +0900 From: Masami Hiramatsu (Google) To: Bradley Morgan Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH v2] lib/bootconfig: fix undefined behavior involving NULL pointer arithmetic Message-Id: <20260701075843.a308d7dadf327eda4015236b@kernel.org> In-Reply-To: <20260630174746.14795-1-include@grrlz.net> References: <20260630174746.14795-1-include@grrlz.net> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Tue, 30 Jun 2026 17:47:46 +0000 Bradley Morgan wrote: > When xbc_snprint_cmdline() is called during the size-probing phase > (with buf = NULL and size = 0), the function computes the end pointer > as 'buf + size' (NULL + 0) and repeatedly advances 'buf' via 'buf += ret'. > > Under the C standard, performing pointer arithmetic on a NULL pointer is > undefined behavior. While harmless inside the kernel, this code is also > compiled into the userspace host tool 'tools/bootconfig', where host > compilers with UBSan or FORTIFY_SOURCE enabled abort the build when they > detect NULL pointer arithmetic. > > Fix this by guarding the pointer arithmetic so 'buf' is only advanced when > non-NULL, and track the running written length in a separate 'len' counter > for the return value (which cannot be recovered from pointer math when > 'buf' is NULL). The rest() helper and snprintf call sites are unchanged. > > Fixes: 51887d03aca1 ("bootconfig: init: Allow admin to use bootconfig for kernel command line") > Cc: stable@vger.kernel.org > Assisted-by: GLM:glm-5.2 > Signed-off-by: Bradley Morgan Thanks for the fix! Let me pick this to bootconfig/fixes. Thank you, > --- > lib/bootconfig.c | 13 +++++++++---- > 1 file changed, 9 insertions(+), 4 deletions(-) > > Changes since v1: > - Got the big guns out! :) (see Assisted-by). > - Addressed review from Masami Hiramatsu and Breno Leitao. > > diff --git a/lib/bootconfig.c b/lib/bootconfig.c > index f445b7703fdd..c913259c80ce 100644 > --- a/lib/bootconfig.c > +++ b/lib/bootconfig.c > @@ -427,8 +427,9 @@ static char xbc_namebuf[XBC_KEYLEN_MAX] __initdata; > int __init xbc_snprint_cmdline(char *buf, size_t size, struct xbc_node *root) > { > struct xbc_node *knode, *vnode; > - char *end = buf + size; > + char *end = buf ? buf + size : NULL; > const char *val, *q; > + size_t len = 0; > int ret; > > xbc_node_for_each_key_value(root, knode, val) { > @@ -442,7 +443,9 @@ int __init xbc_snprint_cmdline(char *buf, size_t size, struct xbc_node *root) > ret = snprintf(buf, rest(buf, end), "%s ", xbc_namebuf); > if (ret < 0) > return ret; > - buf += ret; > + len += ret; > + if (buf) > + buf += ret; > continue; > } > xbc_array_for_each_value(vnode, val) { > @@ -456,11 +459,13 @@ int __init xbc_snprint_cmdline(char *buf, size_t size, struct xbc_node *root) > xbc_namebuf, q, val, q); > if (ret < 0) > return ret; > - buf += ret; > + len += ret; > + if (buf) > + buf += ret; > } > } > > - return buf - (end - size); > + return len; > } > #undef rest > > -- > 2.53.0 > -- Masami Hiramatsu (Google)