From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: passt.top; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: passt.top; dkim=pass (1024-bit key; unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256 header.s=mimecast20190719 header.b=az/D0aDy; dkim-atps=neutral Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by passt.top (Postfix) with ESMTPS id 8A70C5A0619 for ; Mon, 24 Aug 2026 15:45:27 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1787579126; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=2ffzAkdrry4DuCWqJdK595Agu6v92CjrL7A8jxNXIAc=; b=az/D0aDyxp1P5R5xC4+ANB0z9kjq6FR5dWkO9nsNQ/THf3b679Z4zATMcf7d0Scn2hNeTL JyLxg/R2C/BqlFD9np+i8G5kfU1VqM75J56PY5k29f2W4ZCKMCoKHquLvGI+SaINPeEGhx iY/GCbEU37jSVBXMpzS85its4D9uI+c= Received: from mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-313-nhZ76AqJPYGyy_G15nPMdg-1; Mon, 24 Aug 2026 09:45:21 -0400 X-MC-Unique: nhZ76AqJPYGyy_G15nPMdg-1 X-Mimecast-MFC-AGG-ID: nhZ76AqJPYGyy_G15nPMdg_1787579120 Received: from mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.12]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id D6C15180ACCC; Mon, 24 Aug 2026 13:45:20 +0000 (UTC) Received: from anskuma-thinkpadp1gen7.bengluru.csb (unknown [10.74.80.6]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 770E91955F0F; Mon, 24 Aug 2026 13:45:15 +0000 (UTC) From: Anshu Kumari To: sbrivio@redhat.com, passt-dev@passt.top, anskuma@redhat.com Subject: [PATCH v6 6/6] dhcp: Add RFC 3396 option splitting for concatenation-requiring options Date: Mon, 24 Aug 2026 19:14:34 +0530 Message-ID: <20260824134436.282300-7-anskuma@redhat.com> In-Reply-To: <20260824134436.282300-1-anskuma@redhat.com> References: <20260824134436.282300-1-anskuma@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: u9DT3fXlXsXZvjN7JfBStiTDDNCfjomN1UKDnoAHSDw_1787579120 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: 8bit content-type: text/plain; charset="US-ASCII"; x-default=true Message-ID-Hash: WBAZ7MXC3LPVME5GAUB5HRDS272ENJVT X-Message-ID-Hash: WBAZ7MXC3LPVME5GAUB5HRDS272ENJVT X-MailFrom: anskuma@redhat.com X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header CC: david@gibson.dropbear.id.au, jmaloy@redhat.com, lvivier@redhat.com X-Mailman-Version: 3.3.8 Precedence: list List-Id: Development discussion and patches for passt Archived-At: Archived-At: List-Archive: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: Implement option splitting per RFC 3396 for options that may exceed 255 bytes. A new concat_req[] lookup table marks options requiring concatenation (currently option 81, Client FQDN per RFC 4702). The opts[].s buffer is resized from 255 to 497 bytes (OPT_CONCAT_MAX) to hold the maximum data that can be split across the options field, file field, and sname field. When a concatenation-requiring option does not fit as a single option in any field, fill() calls fill_split() to split it across fields in RFC 3396 order: options field first, then file, then sname. Link: https://bugs.passt.top/show_bug.cgi?id=192 Signed-off-by: Anshu Kumari --- v6: - Merged v5 patches 6/7 and 7/7 into a single patch. - Replaced DHCP_OPT_STR_CONCAT enum value and is_concat_opt() helper with a concat_req[] boolean lookup table. - Used MIN() macro instead of ternary for chunk size. - Fixed space calculation to account for 2-byte code+length overhead per chunk. v5: - New patch: implement option splitting per RFC 3396 for options exceeding 255 bytes - Add DHCP_OPT_STR_CONCAT type, is_concat_opt(), fill_split() helpers - Resize opts[].s from 255 to OPT_CONCAT_MAX (497) bytes - Add /* fallthrough */ between DHCP_OPT_STR and DHCP_OPT_STR_CONCAT case --- dhcp.c | 99 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 98 insertions(+), 1 deletion(-) diff --git a/dhcp.c b/dhcp.c index 43ce133..eda04d1 100644 --- a/dhcp.c +++ b/dhcp.c @@ -35,6 +35,11 @@ #include "dhcp.h" #include "parse.h" +/* RFC 3396: maximum option data that can be split across options field, + * file field, and sname field (minus code+length overhead per portion). + */ +#define OPT_CONCAT_MAX 497 + /** * enum opt_state - DHCP option state * @OPT_UNSET: Option not configured @@ -59,7 +64,7 @@ enum opt_state { struct opt { int sent; int slen; - uint8_t s[255]; + uint8_t s[OPT_CONCAT_MAX]; int clen; uint8_t c[255]; enum opt_state state; @@ -215,6 +220,13 @@ static const enum dhcp_opt_type dhcp_opt_types[] = { [252] = DHCP_OPT_STR, /* WPAD URL */ }; +/** + * concat_req - Options requiring RFC 3396 concatenation, indexed by code + */ +static const bool concat_req[256] = { + [81] = true, /* Client FQDN (RFC 4702, Section 2) */ +}; + /** * dhcp_opt_parse() - Parse a DHCP option value * @code: DHCP option code @@ -309,6 +321,9 @@ static int dhcp_opt_parse(uint8_t code, const char *str, case DHCP_OPT_STR: slen = strlen(str); + if (!concat_req[code] && slen > 255) + return -1; + if (slen >= buf_len) return -1; @@ -442,6 +457,40 @@ enum dhcp_overload { DHCP_OVERLOAD_SNAME = 2, }; +/** + * fill_split() - Write a split portion of an option into a buffer + * @buf: Buffer to write into + * @size: Usable size of @buf + * @o: Option number (code) + * @offset: Current offset within @buf, updated on write + * @data: Pointer to remaining option data to write + * @remaining: Bytes of option data still to write + * + * Return: number of data bytes written (excluding code+length header) + */ +static size_t fill_split(uint8_t *buf, size_t size, int o, int *offset, + const uint8_t *data, size_t remaining) +{ + size_t avail, chunk; + + if (*offset + 2 >= (int)size) + return 0; + + avail = size - *offset - 2; + chunk = MIN(remaining, avail); + if (!chunk) + return 0; + + buf[*offset] = o; + buf[*offset + 1] = chunk; + *offset += 2; + + memcpy(buf + *offset, data, chunk); + *offset += chunk; + + return chunk; +} + /** * fill() - Fill options in message, with overload into file/sname if needed * @m: Message to fill @@ -495,6 +544,54 @@ static int fill(struct msg *m, enum dhcp_overload *overload, bool has_bootfile) } } + /* RFC 3396: split concatenation-requiring options that didn't fit + * as a single option. Split order: options, file, sname. + */ + for (o = 0; (size_t)o < ARRAY_SIZE(opts); o++) { + size_t file_cap, sname_cap, total, written; + + if (opts[o].state == OPT_UNSET || opts[o].sent || + !concat_req[o]) + continue; + + sname_cap = sizeof(m->sname) - 1 > (size_t)sname_off ? + sizeof(m->sname) - 1 - sname_off : 0; + + if (has_bootfile || sizeof(m->file) - 1 <= (size_t)file_off) + file_cap = 0; + else + file_cap = sizeof(m->file) - 1 - file_off; + + total = (size > (size_t)offset ? size - offset - 2 : 0) + + (file_cap > 2 ? file_cap - 2 : 0) + + (sname_cap > 2 ? sname_cap - 2 : 0); + + if (total < (size_t)opts[o].slen) { + debug("DHCP: skipping option %i (no space to split)", + o); + continue; + } + + written = 0; + written += fill_split(m->o, size, o, &offset, + opts[o].s, opts[o].slen); + if (written < (size_t)opts[o].slen && !has_bootfile) + written += fill_split(m->file, + sizeof(m->file) - 1, o, + &file_off, + opts[o].s + written, + opts[o].slen - written); + if (written < (size_t)opts[o].slen) + written += fill_split(m->sname, + sizeof(m->sname) - 1, o, + &sname_off, + opts[o].s + written, + opts[o].slen - written); + + if (written >= (size_t)opts[o].slen) + opts[o].sent = 1; + } + /* Report any options that could not be sent */ for (o = 0; (size_t)o < ARRAY_SIZE(opts); o++) { if (opts[o].state != OPT_UNSET && !opts[o].sent) -- 2.55.0