* [PATCH v4 1/2] dhcpv6: Add --dhcpv6-opt with option type table and value parser
2026-10-06 9:04 [PATCH v4 0/2] [PATCH 0/2] dhcpv6: Add --dhcpv6-opt for custom DHCPv6 options Anshu Kumari
@ 2026-10-06 9:04 ` Anshu Kumari
2026-10-06 9:04 ` [PATCH v4 2/2] dhcpv6: Inject custom options into DHCPv6 replies Anshu Kumari
1 sibling, 0 replies; 3+ messages in thread
From: Anshu Kumari @ 2026-10-06 9:04 UTC (permalink / raw)
To: sbrivio, passt-dev; +Cc: lvivier, anskuma
Introduce the --dhcpv6-opt flag that allows setting arbitrary DHCPv6
options from command-line in the form [--dhcpv6-opt CODE,VALUE].
Add a type lookup table mapping option codes to value types (IPv6,
IPv6 list, integer, string, vendor class, length-prefixed string
list) and dhcpv6_opt_parse() to convert CLI strings to binary wire
format. If the same option code is given more than once, the
last value wins.
Link: https://bugs.passt.top/show_bug.cgi?id=192
Signed-off-by: Anshu Kumari <anskuma@redhat.com>
---
v4:
- The dhcpv6_opt_code < 1 check was replaced with proper validation:
dhcpv6_opt_code == 0 || dhcpv6_opt_code > UINT16_MAX in conf.c
- All uint16_t/uint32_t writes to byte buffers now use intermediate
variables + memcpy() instead of direct pointer casts.
- The DHCPV6_OPT_STR case now uses slen > buf_len instead of slen >= buf_len.
- Option 17 (Vendor-specific Info) excluded.
- A separate char optbuf[512] was added in conf_print() instead of
reusing the small INANY_ADDRSTRLEN-sized buf for option rendering.
- inet_ntop() return value checked.
- Uses off += strlen(buf + off) instead of off = strlen(buf) in
the IPv6 list rendering loop.
- Iterator macro added — for_each_in6_off(off, len).
- The addr and af variables are declared at function scope
in dhcpv6_opt_parse() rather than inside block wrappers.
- snprintf() alignment and line formatting.
v3:
- Use parse_unsigned(), parse_literal(), parse_eoi() from parse.c
instead of manual strtoul()/errno/strchr() in dhcpv6_opt_parse()
for UINT and VENDOR_CLASS cases.
- Store options as pre-parsed binary in a static array indexed by
option code, instead of storing raw strings.
- Add dhcpv6_opt_to_str() to render binary option values back to
printable strings for startup logging in conf_print().
v2:
- Renamed custom_v6opts to dhcpv6_opts, MAX_CUSTOM_DHCPV6_OPTS
to MAX_DHCPV6_OPTS.
- Dropped val/len from ctx struct.
- Moved dhcpv6_add_option() to conf.c as static
conf_dhcpv6_option().
- Made dhcpv6_opt_parse() non-static, declared in dhcpv6.h
- Omitted explicit [256] from dhcpv6_opt_types[].
- Moved chunk declaration into while block.
- Removed redundant !slen check in DHCPV6_OPT_STR case.
- All errors in dhcpv6_opt_parse() return -1, removed die()
calls.
---
conf.c | 26 ++++-
dhcpv6.c | 339 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
dhcpv6.h | 2 +
passt.1 | 31 +++++
4 files changed, 397 insertions(+), 1 deletion(-)
diff --git a/conf.c b/conf.c
index faf26814..dba62bf8 100644
--- a/conf.c
+++ b/conf.c
@@ -47,6 +47,7 @@
#include "lineread.h"
#include "isolation.h"
#include "log.h"
+#include "dhcpv6.h"
#include "vhost_user.h"
#include "epoll_ctl.h"
#include "conf.h"
@@ -632,7 +633,8 @@ static void usage(const char *name, FILE *f, int status)
" -S, --search LIST Space-separated list, search domains\n"
" a single, empty option disables the DNS search list\n"
" -H, --hostname NAME Hostname to configure client with\n"
- " --fqdn NAME FQDN to configure client with\n");
+ " --fqdn NAME FQDN to configure client with\n"
+ " --dhcpv6-opt CODE,VAL Set DHCPv6 option CODE to VAL\n");
if (strstr(name, "pasta"))
FPRINTF(f, " default: don't use any search list\n");
else
@@ -800,6 +802,7 @@ enum passt_modes conf_mode(int argc, char *argv[])
static void conf_print(const struct ctx *c)
{
char buf[INANY_ADDRSTRLEN];
+ char optbuf[512];
int i;
if (c->fd_control_listen >= 0)
@@ -900,6 +903,10 @@ static void conf_print(const struct ctx *c)
info(" our link-local: %s",
inet_ntop(AF_INET6, &c->ip6.our_tap_ll,
buf, sizeof(buf)));
+ for (i = 1; i < UINT16_MAX; i++) {
+ if (dhcpv6_opt_to_str(i, optbuf, sizeof(optbuf)))
+ info(" option %u: %s", i, optbuf);
+ }
dns6:
for (i = 0; i < ARRAY_SIZE(c->ip6.dns); i++) {
@@ -1348,6 +1355,7 @@ void conf(struct ctx *c, int argc, char **argv)
{"stats", required_argument, NULL, 31 },
{"conf-path", required_argument, NULL, 'c' },
{"chroot-fallback", no_argument, NULL, 32 },
+ {"dhcpv6-opt", required_argument, NULL, 35 },
{ 0 },
};
const char *optstring = "+dqfel:hs:c:F:I:p:P:m:a:n:M:g:i:o:D:S:H:461t:u:T:U:";
@@ -1589,6 +1597,22 @@ void conf(struct ctx *c, int argc, char **argv)
case 32:
c->chroot_fallback = true;
break;
+ case 35: {
+ unsigned long dhcpv6_opt_code;
+
+ p = optarg;
+
+ if (!parse_unsigned(&p, 0, &dhcpv6_opt_code) ||
+ !parse_literal(&p, ","))
+ die("--dhcpv6-opt requires CODE,VALUE format");
+
+ if (dhcpv6_opt_code == 0 ||
+ dhcpv6_opt_code > UINT16_MAX)
+ die("Invalid DHCPv6 option code: %s", optarg);
+
+ dhcpv6_set_opt(dhcpv6_opt_code, p);
+ break;
+ }
case 'd':
c->debug = 1;
c->quiet = 0;
diff --git a/dhcpv6.c b/dhcpv6.c
index 29c7e320..abc45813 100644
--- a/dhcpv6.c
+++ b/dhcpv6.c
@@ -31,6 +31,8 @@
#include "passt.h"
#include "tap.h"
#include "log.h"
+#include "inany.h"
+#include "parse.h"
/**
* struct opt_hdr - DHCPv6 option header
@@ -63,6 +65,11 @@ struct opt_hdr {
#define OPT_MAX_SIZE IPV6_MIN_MTU - (sizeof(struct ipv6hdr) + \
UDP_MSG_HDR_SIZE)
+#define for_each_in6_off(off, len) \
+ for ((off) = 0; \
+ (off) + sizeof(struct in6_addr) <= (unsigned int)(len); \
+ (off) += sizeof(struct in6_addr))
+
/**
* struct opt_client_id - DHCPv6 Client Identifier option
* @hdr: Option header
@@ -278,6 +285,338 @@ static struct resp_not_on_link_t {
{ 0, },
};
+/**
+ * enum dhcpv6_opt_type - DHCPv6 option value types
+ * @DHCPV6_OPT_NONE: Unsupported or unknown option
+ * @DHCPV6_OPT_STR: Variable-length string
+ * @DHCPV6_OPT_IPV6: Single IPv6 address
+ * @DHCPV6_OPT_IPV6_LIST: Multiple IPv6 addresses, comma-separated
+ * @DHCPV6_OPT_UINT8: Unsigned 8-bit integer
+ * @DHCPV6_OPT_UINT16: Unsigned 16-bit integer
+ * @DHCPV6_OPT_UINT32: Unsigned 32-bit integer
+ * @DHCPV6_OPT_VENDOR_CLASS: Enterprise number + length-prefixed data
+ * @DHCPV6_OPT_LEN_STR_LIST: Length-prefixed string list
+ */
+enum dhcpv6_opt_type {
+ DHCPV6_OPT_NONE,
+ DHCPV6_OPT_STR,
+ DHCPV6_OPT_IPV6,
+ DHCPV6_OPT_IPV6_LIST,
+ DHCPV6_OPT_UINT8,
+ DHCPV6_OPT_UINT16,
+ DHCPV6_OPT_UINT32,
+ DHCPV6_OPT_VENDOR_CLASS,
+ DHCPV6_OPT_LEN_STR_LIST,
+};
+
+/**
+ * dhcpv6_opt_types - Maps DHCPv6 option code to value type, indexed by code
+ * RFC 8415 Options: 7, 15, 16, 32, 82, 83
+ * RFC 5970 Options: 59, 60
+ * RFC 4075 Options: 31
+ */
+static const enum dhcpv6_opt_type dhcpv6_opt_types[] = {
+ [7] = DHCPV6_OPT_UINT8, /* Preference */
+ [15] = DHCPV6_OPT_LEN_STR_LIST, /* User Class */
+ [16] = DHCPV6_OPT_VENDOR_CLASS, /* Vendor Class */
+ [31] = DHCPV6_OPT_IPV6_LIST, /* SNTP Servers */
+ [32] = DHCPV6_OPT_UINT32, /* Information Refresh Time */
+ [59] = DHCPV6_OPT_STR, /* Boot File URL */
+ [60] = DHCPV6_OPT_LEN_STR_LIST, /* Boot File Params */
+ [82] = DHCPV6_OPT_UINT32, /* SOL_MAX_RT */
+ [83] = DHCPV6_OPT_UINT32, /* INF_MAX_RT */
+};
+
+/**
+ * dhcpv6_opt_parse() - Parse a DHCPv6 option value string into binary
+ * @code: DHCPv6 option code
+ * @str: Value string from command line
+ * @buf: Output buffer for binary value
+ * @buf_len: Size of output buffer
+ *
+ * Return: number of bytes written to @buf, or -1 on error
+ */
+static int dhcpv6_opt_parse(uint16_t code, const char *str,
+ uint8_t *buf, size_t buf_len)
+{
+ enum dhcpv6_opt_type type;
+ union inany_addr addr;
+ unsigned long val;
+ uint16_t slen_net;
+ sa_family_t af;
+ uint8_t width;
+ uint32_t ent;
+ size_t slen;
+ int len;
+
+ if (!*str)
+ return -1;
+
+ if (code >= ARRAY_SIZE(dhcpv6_opt_types))
+ return -1;
+
+ type = dhcpv6_opt_types[code];
+
+ switch (type) {
+ case DHCPV6_OPT_NONE:
+ return -1;
+ case DHCPV6_OPT_IPV6:
+ case DHCPV6_OPT_IPV6_LIST:
+ len = 0;
+
+ do {
+ if (len + sizeof(struct in6_addr) > buf_len)
+ return -1;
+
+ if (!parse_inany_(&str, &addr, &af) || af != AF_INET6)
+ return -1;
+
+ memcpy(buf + len, &addr.a6, sizeof(struct in6_addr));
+ len += sizeof(struct in6_addr);
+
+ if (type == DHCPV6_OPT_IPV6)
+ break;
+ } while (parse_literal(&str, ","));
+
+ if (!len || !parse_eoi(str))
+ return -1;
+
+ return len;
+ case DHCPV6_OPT_UINT8:
+ case DHCPV6_OPT_UINT16:
+ case DHCPV6_OPT_UINT32:
+ if (type == DHCPV6_OPT_UINT8)
+ width = 1;
+ else if (type == DHCPV6_OPT_UINT16)
+ width = 2;
+ else
+ width = 4;
+
+ if (buf_len < width)
+ return -1;
+
+ if (!parse_unsigned(&str, 0, &val) || !parse_eoi(str) ||
+ val >= (1ULL << (width * 8)))
+ return -1;
+
+ if (type == DHCPV6_OPT_UINT16) {
+ uint16_t v16 = htons(val);
+ memcpy(buf, &v16, sizeof(v16));
+ } else if (type == DHCPV6_OPT_UINT32) {
+ uint32_t v32 = htonl(val);
+ memcpy(buf, &v32, sizeof(v32));
+ } else {
+ buf[0] = val;
+ }
+
+ return width;
+ case DHCPV6_OPT_STR:
+ slen = strlen(str);
+
+ if (slen > buf_len)
+ return -1;
+
+ memcpy(buf, str, slen);
+
+ return slen;
+ case DHCPV6_OPT_VENDOR_CLASS:
+ if (!parse_unsigned(&str, 0, &val) ||
+ !parse_literal(&str, ":") || val > UINT32_MAX)
+ return -1;
+
+ slen = strlen(str);
+ if (!slen)
+ return -1;
+
+ len = sizeof(uint32_t) + sizeof(uint16_t) + slen;
+ if ((size_t)len > buf_len)
+ return -1;
+
+ ent = htonl(val);
+ memcpy(buf, &ent, sizeof(ent));
+
+ slen_net = htons(slen);
+ memcpy(buf + sizeof(uint32_t), &slen_net, sizeof(slen_net));
+
+ memcpy(buf + sizeof(uint32_t) + sizeof(uint16_t), str, slen);
+
+ return len;
+ case DHCPV6_OPT_LEN_STR_LIST:
+ len = 0;
+
+ while (*str) {
+ slen = strcspn(str, ",");
+ if (!slen)
+ return -1;
+
+ if (len + (int)(sizeof(uint16_t) + slen) > (int)buf_len)
+ return -1;
+
+ slen_net = htons(slen);
+ memcpy(buf + len, &slen_net, sizeof(slen_net));
+ len += sizeof(uint16_t);
+
+ memcpy(buf + len, str, slen);
+ len += slen;
+
+ str += slen;
+ if (*str == ',')
+ str++;
+ }
+
+ if (!len)
+ return -1;
+
+ return len;
+ }
+
+ return -1;
+}
+
+/**
+ * struct dhcpv6_user_opts - User-specified DHCPv6 options from --dhcpv6-opt
+ * @val: Binary option value in wire format
+ * @len: Length of @val in bytes, 0 if not set
+ */
+static struct {
+ uint8_t val[UINT16_MAX];
+ int len;
+} dhcpv6_user_opts[ARRAY_SIZE(dhcpv6_opt_types)];
+
+/**
+ * dhcpv6_opt_to_str() - Render a binary DHCPv6 option value to printable string
+ * @code: DHCPv6 option code
+ * @buf: Output string buffer
+ * @buf_len: Size of output buffer
+ *
+ * Return: pointer to @buf if option is set, NULL otherwise
+ */
+const char *dhcpv6_opt_to_str(uint16_t code, char *buf, size_t buf_len)
+{
+ enum dhcpv6_opt_type type;
+ unsigned int i;
+ uint16_t slen;
+ int off = 0;
+
+ if (code >= ARRAY_SIZE(dhcpv6_user_opts) ||
+ !dhcpv6_user_opts[code].len)
+ return NULL;
+
+ type = dhcpv6_opt_types[code];
+
+ switch (type) {
+ case DHCPV6_OPT_IPV6:
+ case DHCPV6_OPT_IPV6_LIST:
+ for_each_in6_off(i, dhcpv6_user_opts[code].len) {
+ if (off) {
+ if (off + 1 >= (int)buf_len)
+ return NULL;
+ buf[off++] = ',';
+ }
+ if (!inet_ntop(AF_INET6,
+ dhcpv6_user_opts[code].val + i,
+ buf + off, buf_len - off))
+ return NULL;
+ off += strlen(buf + off);
+ }
+ return buf;
+ case DHCPV6_OPT_UINT8:
+ case DHCPV6_OPT_UINT16:
+ case DHCPV6_OPT_UINT32: {
+ uint32_t val = 0;
+
+ if (dhcpv6_user_opts[code].len == 1) {
+ val = dhcpv6_user_opts[code].val[0];
+ } else if (dhcpv6_user_opts[code].len == 2) {
+ uint16_t v16;
+ memcpy(&v16, dhcpv6_user_opts[code].val, sizeof(v16));
+ val = ntohs(v16);
+ } else if (dhcpv6_user_opts[code].len == 4) {
+ memcpy(&val, dhcpv6_user_opts[code].val, sizeof(val));
+ val = ntohl(val);
+ }
+
+ (void)snprintf(buf, buf_len, "%u", val);
+ return buf;
+ }
+ case DHCPV6_OPT_STR:
+ (void)snprintf(buf, buf_len, "%.*s",
+ dhcpv6_user_opts[code].len,
+ dhcpv6_user_opts[code].val);
+ return buf;
+ case DHCPV6_OPT_VENDOR_CLASS: {
+ uint32_t ent;
+ int doff;
+
+ if (dhcpv6_user_opts[code].len <
+ (int)(sizeof(uint32_t) + sizeof(uint16_t)))
+ return NULL;
+
+ memcpy(&ent, dhcpv6_user_opts[code].val, sizeof(ent));
+ memcpy(&slen, dhcpv6_user_opts[code].val + sizeof(uint32_t),
+ sizeof(slen));
+ doff = sizeof(uint32_t) + sizeof(uint16_t);
+
+ (void)snprintf(buf, buf_len, "%u:%.*s",
+ ntohl(ent), ntohs(slen),
+ dhcpv6_user_opts[code].val + doff);
+ return buf;
+ }
+ case DHCPV6_OPT_LEN_STR_LIST:
+ off = 0;
+ i = 0;
+
+ while (i + sizeof(uint16_t) <=
+ (unsigned int)dhcpv6_user_opts[code].len) {
+ memcpy(&slen, dhcpv6_user_opts[code].val + i,
+ sizeof(slen));
+ slen = ntohs(slen);
+ i += sizeof(uint16_t);
+
+ if (i + slen > (unsigned int)dhcpv6_user_opts[code].len)
+ break;
+
+ if (off) {
+ if (off + 1 >= (int)buf_len)
+ return NULL;
+ buf[off++] = ',';
+ }
+ if (off + slen >= (int)buf_len)
+ return NULL;
+ memcpy(buf + off, dhcpv6_user_opts[code].val + i,
+ slen);
+ off += slen;
+ i += slen;
+ }
+ buf[off] = '\0';
+ return buf;
+ default:
+ return NULL;
+ }
+}
+
+/**
+ * dhcpv6_set_opt() - Parse and store a user-specified DHCPv6 option
+ * @code: DHCPv6 option code
+ * @val_str: Value string from command line
+ */
+void dhcpv6_set_opt(uint16_t code, const char *val_str)
+{
+ int ret;
+
+ if (code >= ARRAY_SIZE(dhcpv6_opt_types) ||
+ dhcpv6_opt_types[code] == DHCPV6_OPT_NONE)
+ die("DHCPv6 option %u is not supported", code);
+
+ ret = dhcpv6_opt_parse(code, val_str,
+ dhcpv6_user_opts[code].val,
+ sizeof(dhcpv6_user_opts[code].val));
+ if (ret < 0)
+ die("Invalid value for DHCPv6 option %u: %s", code, val_str);
+
+ dhcpv6_user_opts[code].len = ret;
+}
+
/**
* dhcpv6_opt() - Get option from DHCPv6 message
* @data: Buffer with options, set to matching option on return
diff --git a/dhcpv6.h b/dhcpv6.h
index 1015a1a7..973c477c 100644
--- a/dhcpv6.h
+++ b/dhcpv6.h
@@ -9,5 +9,7 @@
int dhcpv6(struct ctx *c, struct iov_tail *data,
const struct in6_addr *saddr, const struct in6_addr *daddr);
void dhcpv6_init(const struct ctx *c);
+void dhcpv6_set_opt(uint16_t code, const char *val_str);
+const char *dhcpv6_opt_to_str(uint16_t code, char *buf, size_t buf_len);
#endif /* DHCPV6_H */
diff --git a/passt.1 b/passt.1
index 53e072a9..249ed5cf 100644
--- a/passt.1
+++ b/passt.1
@@ -440,6 +440,37 @@ Send \fIname\fR as DHCP option 12 (hostname).
FQDN to configure the client with.
Send \fIname\fR as Client FQDN: DHCP option 81 and DHCPv6 option 39.
+.TP
+.BR \-\-dhcpv6-opt " " \fICODE\fR,\fIVALUE\fR
+Set DHCPv6 option \fICODE\fR to \fIVALUE\fR. The value format depends
+on the option type and is determined automatically from the option code.
+Multiple IPv6 addresses are comma-separated.
+This option can be specified multiple times. If the same option code is
+given more than once, the last value wins.
+.RS
+.TP
+.B String options
+59 (Boot File URL, RFC 5970)
+.TP
+.B Length-prefixed string list options (comma-separated entries)
+15 (User Class, RFC 8415), 60 (Boot File Params, RFC 5970).
+Each comma-separated entry is encoded with a 2-byte length prefix.
+Example: \fB\-\-dhcpv6-opt 15,class1,class2\fR.
+.TP
+.B Vendor class options (ENTERPRISE:DATA format)
+16 (Vendor Class, RFC 8415).
+VALUE is \fIENTERPRISE\fR:\fIDATA\fR where \fIENTERPRISE\fR is the IANA
+Private Enterprise Number and \fIDATA\fR is the vendor class string.
+Example: \fB\-\-dhcpv6-opt 16,0:HTTPClient\fR for UEFI HTTP Boot.
+.TP
+.B IPv6 address list options (comma-separated)
+31 (SNTP Servers)
+.TP
+.B Integer options
+7 (Preference, 8-bit), 32 (Information Refresh Time, 32-bit),
+82 (SOL_MAX_RT, 32-bit), 83 (INF_MAX_RT, 32-bit)
+.RE
+
.TP
.BR \-t ", " \-\-tcp-ports " " \fIspec
Configure TCP port forwarding to guest or namespace. \fIspec\fR can be either:
--
2.55.0
^ permalink raw reply [flat|nested] 3+ messages in thread