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 7DAC92E739D; Tue, 30 Jun 2026 23:26:14 +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=1782861975; cv=none; b=BAgi6ZOoRpH2NFIa7oH2RaqXTDfxmUKv0hrFIUEXrAxvuoZ+7kSn453xdCZI3zQ651RYYJo8ed2ODbNaGh42TYYC3+ubuFPC9wv5eO3SI+tIg/UxPNJxuxoJEelPqgGEjZ0xZ/UOErUoN0UMp5Z54AmxVRRDlix05g+Gngx74Mk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782861975; c=relaxed/simple; bh=9vGalAOsLPcJUq7KMLEtC4VkqUsqCi3zY6br5fZ9gsY=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=McxMU9Ne+GM75VNAzEOeAPYeV8xdEcXBvVIP6rstr9mriXYG8LbUxHM/msRIAp8w8vFtWkqyK5viT/LFr5qe+/5LC/cZEYrRJEn9PPb4we1RBs5onyr4lpk81keyA2BmTfN9f8a9kCq1S6Hz8MKkkbHHbl4Y2PF44Ata/g1H93o= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ibuSdTQV; 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="ibuSdTQV" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CA7AC1F000E9; Tue, 30 Jun 2026 23:26:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1782861974; bh=UjhfWxTf1PrShdtV9sLZkODcbJd9iyF248wEEnzzhj0=; h=Date:From:To:Cc:Subject:In-Reply-To:References; b=ibuSdTQVWk7cvzki6/7/Swjg81STECAO7y1ETLLCTy3OFpEC7Ee0yUCUujgFv8P1s L3q1OC+dx3cN1Bf5aOy3ogR3Ma1RDSfXZbDIAWssLtcybvL77SI7kIdmZwMW5oeRkw kvuXq+D7y0cg0X+lfv+/RGfiEz9KpgHCZ25HivTCp4RHcC5uAq7p7rrro05SXO6kCw DM6/OvYDXevD8bp+67zf1DAkYgRQJ1AlJganrICYf+ft6Ub0OsPIMA4mjecUc3a5bM UfpzN0naSzEJ2HpO//B+k/TU369v40wmqIdmLDqqDItbhK+3N0OvVwHolZHGee8XbD 5rrqUOdvlJbbQ== Date: Wed, 1 Jul 2026 08:26:11 +0900 From: Masami Hiramatsu (Google) To: Masami Hiramatsu (Google) Cc: Bradley Morgan , 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: <20260701082611.6575e0f37541014f67830bdc@kernel.org> In-Reply-To: <20260701075843.a308d7dadf327eda4015236b@kernel.org> References: <20260630174746.14795-1-include@grrlz.net> <20260701075843.a308d7dadf327eda4015236b@kernel.org> 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 Wed, 1 Jul 2026 07:58:43 +0900 Masami Hiramatsu (Google) wrote: > 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. Sorry, I eventually decided to pick Breno's fix [1], because it fixes the same issue earlier (in bootconfig/core) and has a well documented comment on the code. [1] https://lore.kernel.org/all/20260626-bootconfig_using_tools-v7-1-24ab72139c29@debian.org/ BTW, I decided to have several branches for bootconfig and probes. bootconfig/core is a core development branch, which is the main branch. The patches in this branch is for development, including new features and fixes. (but fixes will be moved to */fixes soon.) bootconfig/fixes is for a branch to manage fixes. This will be sent to Linus soon (for urgent fix), or after releasing -rc. bootconfig/for-next is for new features or cleanups, for preparing the next merge window, and for merge test in linux-next. If you make any patches, please check the bootconfig/core at first, and check bootconfig/fixes for fix. Note: The core is usually forcibly updated, actively rebased on top of bootconfig/fixes. The for-next is not so frequently updated, but can be forced update for fixing merge conflict etc. The fixes should be solid, but if I made mistakes I will forcibly update it before sending PR. Thank you, > > 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) -- Masami Hiramatsu (Google)