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 664123BBFB6 for ; Tue, 21 Jul 2026 08:57:29 +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=1784624250; cv=none; b=Ha8/b/BgF5BZumu30kZfXJ9EipO3MoAZLpWj6h1MKUU2TNFXyhFhg4B2Gtu7q47PZA1r0C+a1wKpSCHTy63Mswkqy9fDoyBnFdb2Vcq5rZGgS9Gcer5klvZ+r+y4CB0scBtTPv+Iw9L1prOpwhy2FxEB1OrdL3bCsRzmaq8+sLk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784624250; c=relaxed/simple; bh=JPQWQh8MnHHIaUtbSo4OHB5BDGjrS3lpsFnm9UBa1qE=; h=Subject:To:Cc:From:Date:Message-ID:MIME-Version:Content-Type; b=YKrbTcVEBC453AuWcDqblVHrLDOLQklA1+b1t5VgyloyAHIyzxRQoDMWjpD3jPupxrsic0a3tdNF4IRagxT5Q8EGXHljLwq1T808GA1/3coPf1CQpHtHwDuUtbnkzZ54CH2rsI1r857tcvNHhsLwPH/mbgEe3C9ZI3fFBzn4mHE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=0jBthtp+; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="0jBthtp+" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8DC1A1F00A3A; Tue, 21 Jul 2026 08:57:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1784624249; bh=Y2H2AQF2/cKuefc2oplKEeTHEk/VNLYTb63MdBXX3x0=; h=Subject:To:Cc:From:Date; b=0jBthtp+ick3uzxoJD0cj4KVcujL/WZMSeNkMmztVGMSHsaH5wzj00iDF9zT6cCUg hNTCxBt85aybrRK3glRgm8nhwPns+ZwQODUCbvPyk/mMl8IZoQdOCMTCplPnD+y4fD tN40SV9ZLvRFIq6IFeOFvk4Kcqg6lb3K/HLRauus= Subject: FAILED: patch "[PATCH] bootconfig: fix NULL-pointer arithmetic in" failed to apply to 6.18-stable tree To: leitao@debian.org,mhiramat@kernel.org Cc: From: Date: Tue, 21 Jul 2026 10:57:11 +0200 Message-ID: <2026072111-dizzy-spur-667f@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit The patch below does not apply to the 6.18-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.18.y git checkout FETCH_HEAD git cherry-pick -x dec4d8118c179b3d12bca7e609054c6011c4f2ce # git commit -s git send-email --to '' --in-reply-to '2026072111-dizzy-spur-667f@gregkh' --subject-prefix 'PATCH 6.18.y' 'HEAD^..' Possible dependencies: thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From dec4d8118c179b3d12bca7e609054c6011c4f2ce Mon Sep 17 00:00:00 2001 From: Breno Leitao Date: Fri, 26 Jun 2026 05:50:10 -0700 Subject: [PATCH] bootconfig: fix NULL-pointer arithmetic in xbc_snprint_cmdline() 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) diff --git a/lib/bootconfig.c b/lib/bootconfig.c index f445b7703fdd..2ed9ee3dc81c 100644 --- a/lib/bootconfig.c +++ b/lib/bootconfig.c @@ -427,10 +427,18 @@ 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); @@ -439,10 +447,11 @@ 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) { @@ -452,15 +461,15 @@ 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