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 21B1937BE6C for ; Tue, 28 Jul 2026 16:29:49 +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=1785256191; cv=none; b=KnwEFhhqbCgq/TEKTWGApazMnrGjMMUQyR9oycVos4nV+JjtILa7L4b77KShr2L1uvP6cNU7WXCHP0EdEId64yI2YYRQakyG3wcJf/UScBjJv/As/KKeCvmFZHPQ1zY8sNmaYzQ/EviDJp70e8ThBjCsuBe21aEP/dPppEyT51I= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785256191; c=relaxed/simple; bh=tDOy789lAKvxzvnBWfV7jqg7q5cEFH0OYBZElziyUAQ=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=I0dMYxzZxRpvGZL4yInMUxjnXw7ysUJ+zirdG7s1Hy4VIHfx32HN3y+UPFLTFYt8mB08BLtFiVgG24s0XyhISXrbJfHwxVwOfXQ3dUHx66LHwKaSXGnSEk6UmqTflnhaY4E4ort26Te2lpL2K1/zEELNb/S5pmBFc+iTX6JyiFA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=H2tqdtPe; 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="H2tqdtPe" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 26EC51F00A3E; Tue, 28 Jul 2026 16:29:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785256189; bh=HppW+I++3zBE3FND+ZHwBBxdWTlajuQppY13UBsvc54=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=H2tqdtPeOkONFDJ8e6OdqgBdVdMxQuivJW0diFauruufmkJKCDvASIhtjtvyKUuU0 G3GGkyLKuurKI4NmdXyVvSetTOo0ON7zjKEyWR0Jm2xaAZ2IBVDzq4AHmL+hR6NP0w VE3DaPZ7KOA8SAh2a54vSYE5/+fLAyF6jEOLvK8/T0tAZW3plAhgRB4gdG6ej8Lcy2 xOEkte+d5UasbJHdY6hM1aOtDypE/2eUwu7ooXBKaGoDfa96u9Qf+rlJIg6zRKVr7e UtKGWzeJz9zT5o+d6BgrCrlM0FVI9+mBhLagbBU1uBkZRZt77hHg4WbMk9PtGzfufZ 7xQtdovS1XfRg== From: Sasha Levin To: stable@vger.kernel.org Cc: Breno Leitao , "Masami Hiramatsu (Google)" , Sasha Levin Subject: [PATCH 6.18.y 2/2] bootconfig: fix NULL-pointer arithmetic in xbc_snprint_cmdline() Date: Tue, 28 Jul 2026 12:29:46 -0400 Message-ID: <20260728162946.99526-2-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260728162946.99526-1-sashal@kernel.org> References: <2026072111-dizzy-spur-667f@gregkh> <20260728162946.99526-1-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 c149ee8eb55dfc..b4e8e17e29155e 100644 --- a/lib/bootconfig.c +++ b/lib/bootconfig.c @@ -424,10 +424,18 @@ 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); @@ -436,10 +444,11 @@ 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) { @@ -449,15 +458,15 @@ 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