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 D965823BCED for ; Wed, 29 Jul 2026 00:30:30 +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=1785285032; cv=none; b=WdHbqiWgw50eg3RqU6506cIcN6X9D/JZjxfr9GZFhc6JO1WdBCcYJtxuDSMQLLhKVhZeeWM0KtZY5blNWcuytueRlI+yJAKe9H72DkPccdKzED0Mhcq/F7fjBrIXMjqSmADy4KGDkUPeYZIUG31NsqynHAgPqL7lItsy/pqp2Io= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785285032; c=relaxed/simple; bh=sIAGvKCuUgi41smO1FmxNjwWwtt2RfMNcd3jHi83tMQ=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=ohLezr8oYdTfQkmMYgS9+sfJ6ZxtB3/2eakMbGp+1zxZCmNs3EmlLYvPGIzRYVEN2xJ+m/kGVl8nZLvt/qC9X4cgRWRJgy5D4f++3kGTFV2vhciM3/LclMohbUzaTsqF2J7K5SuAPG1Kn8HDxnW8zXNNkhMGoQhQj3SIx0IdG+g= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=IS3kEmdj; 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="IS3kEmdj" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4DD0F1F00A3E; Wed, 29 Jul 2026 00:30:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785285030; bh=mvVnQ3Md/NLIubBZlWd5YIfDD3ru8ksq+JM9f9IRR24=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=IS3kEmdjOnnBpcfmYzBYbcPjIlUGzXiSR8MIqhwri8CtnXtzygU1mEVp1tAlIa58W j0chdY7Tz5io6FfaKR1LZhgc35phAOf7aPDMVcdpRmqWhzSoL2klghpnC5QZ7bHAaP c/OD/ZWnW7w5oE7wjqeNeZY0Tgu+Y58usuJ7gyxKPg+VB33SN82xt+4ZN/bbdOnJBu g21K44TV27BqY7n0fHIwCuFPvQs2gQEO9Kb2VfNnlAO0c0aqOREGr/OdipjIj6RdOy kFyviWqDV8p8kjNCMBM0gMv86op6ZhwOhDO8qPSV5JwzgYj/voLTU9VVh32G2XWwnF CNf/PJv+JqzQQ== From: Sasha Levin To: stable@vger.kernel.org Cc: Breno Leitao , "Masami Hiramatsu (Google)" , Sasha Levin Subject: [PATCH 5.10.y 3/3] bootconfig: fix NULL-pointer arithmetic in xbc_snprint_cmdline() Date: Tue, 28 Jul 2026 20:30:27 -0400 Message-ID: <20260729003027.887848-3-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260729003027.887848-1-sashal@kernel.org> References: <2026072113-duvet-tattling-a13a@gregkh> <20260729003027.887848-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Breno Leitao [ Upstream commit dec4d8118c179b3d12bca7e609054c6011c4f2ce ] xbc_snprint_cmdline() is meant to be called twice: first with buf=NULL, size=0 to probe the rendered length, then with a real buffer to fill it (the standard snprintf() two-pass pattern). The probe call makes the function compute "buf + size" (NULL + 0) and, on every iteration, advance "buf += ret" from that NULL base and pass the result back into snprintf(). Pointer arithmetic on a NULL pointer is undefined behavior. It is harmless in the in-kernel callers today, but the follow-up patches run this same code in the userspace tools/bootconfig parser at kernel build time, where host UBSan / FORTIFY_SOURCE abort the build. Track a running written length (size_t) instead of mutating @buf, and only form "buf + len" when @buf is non-NULL. snprintf(NULL, 0, ...) is itself well defined and returns the would-be length, so the two-pass "probe then fill" usage returns identical byte counts. Link: https://lore.kernel.org/all/20260626-bootconfig_using_tools-v7-1-24ab72139c29@debian.org/ Fixes: 51887d03aca1 ("bootconfig: init: Allow admin to use bootconfig for kernel command line") Cc: stable@vger.kernel.org Signed-off-by: Breno Leitao Signed-off-by: Masami Hiramatsu (Google) Signed-off-by: Sasha Levin --- lib/bootconfig.c | 23 ++++++++++++++++------- 1 file changed, 16 insertions(+), 7 deletions(-) diff --git a/lib/bootconfig.c b/lib/bootconfig.c index 3b3d666e207618..f6bede03c69265 100644 --- a/lib/bootconfig.c +++ b/lib/bootconfig.c @@ -348,10 +348,18 @@ 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; const char *val, *q; + size_t len = 0; int ret; + /* + * Track the running written length rather than advancing @buf, so we + * never form "buf + size" or "buf += ret" while @buf is NULL (the + * size-probe call passes buf=NULL, size=0). NULL pointer arithmetic + * is undefined behavior and trips host UBSan / FORTIFY_SOURCE when + * this renderer runs at kernel build time. snprintf(NULL, 0, ...) + * itself is well defined and returns the would-be length. + */ xbc_node_for_each_key_value(root, knode, val) { ret = xbc_node_compose_key_after(root, knode, xbc_namebuf, XBC_KEYLEN_MAX); @@ -360,10 +368,11 @@ int __init xbc_snprint_cmdline(char *buf, size_t size, struct xbc_node *root) vnode = xbc_node_get_child(knode); if (!vnode) { - ret = snprintf(buf, rest(buf, end), "%s ", xbc_namebuf); + ret = snprintf(buf ? buf + len : NULL, rest(len, size), + "%s ", xbc_namebuf); if (ret < 0) return ret; - buf += ret; + len += ret; continue; } xbc_array_for_each_value(vnode, val) { @@ -373,15 +382,15 @@ int __init xbc_snprint_cmdline(char *buf, size_t size, struct xbc_node *root) * whitespace. */ q = strpbrk(val, " \t\r\n") ? "\"" : ""; - ret = snprintf(buf, rest(buf, end), "%s=%s%s%s ", - xbc_namebuf, q, val, q); + ret = snprintf(buf ? buf + len : NULL, rest(len, size), + "%s=%s%s%s ", xbc_namebuf, q, val, q); if (ret < 0) return ret; - buf += ret; + len += ret; } } - return buf - (end - size); + return len; } #undef rest -- 2.53.0