On Tue, May 26, 2026 at 06:01:10PM +0530, Anshu Kumari wrote: > Add an RFC 2132 type lookup table mapping DHCP option codes to their > expected value formats, and a dhcp_opt_parse() function that converts > CLI string values into their binary wire representation. > > Wire dhcp_opt_parse() into the --dhcp-opt handler so that values are > validated and encoded at configuration time. > > Link: https://bugs.passt.top/show_bug.cgi?id=192 > Signed-off-by: Anshu Kumari Laurent's comments seconded, a few other ones here. > --- > v2: > - Replaced struct lookup table + dhcp_opt_type_lookup() function with flat dhcp_opt_types[256] array indexed by code. > - Consolidated DHCP_OPT_UINT8/UINT16/UINT32 into single DHCP_OPT_INTEGER with dhcp_opt_int_width[256] table. > - Dropped DHCP_OPT_ROUTES / option 121 entirely. > - Added kerneldoc for enum dhcp_opt_type values. > - Removed curly braces from switch cases, declarations before switch. > - Added newlines before return statements. > - Changed IP list delimiter from space to comma (--dhcp-opt 6,1.1.1.1,8.8.8.8). > - Defined DHCP_OPT_PARSE_BUF constant for bare 1024. > - Added len and val[255] fields to struct here (moved from patch 1). > - Added kerneldoc for @custom_opts.len and @custom_opts.val. > - Wired dhcp_opt_parse() into case 32 (--dhcp-boot) to populate val/len. > --- > conf.c | 16 ++++++ > dhcp.c | 148 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++ > dhcp.h | 17 +++++++ > passt.h | 4 ++ > 4 files changed, 185 insertions(+) > > diff --git a/conf.c b/conf.c > index ae8ee26..3a5f45d 100644 > --- a/conf.c > +++ b/conf.c > @@ -1266,6 +1266,7 @@ void conf(struct ctx *c, int argc, char **argv) > char *end; > uid_t uid; > gid_t gid; > + int len; > > > if (c->mode == MODE_PASTA) > @@ -1482,7 +1483,14 @@ void conf(struct ctx *c, int argc, char **argv) > die("Too many DHCP options (max %d)", > MAX_CUSTOM_DHCP_OPTS); > > + ret = dhcp_opt_parse(67, optarg, > + c->custom_opts[c->custom_opts_count].val, > + sizeof(c->custom_opts[0].val)); > + if (ret < 0) > + die("Invalid boot file value: %s", optarg); > + > c->custom_opts[c->custom_opts_count].code = 67; > + c->custom_opts[c->custom_opts_count].len = ret; > if (snprintf_check(c->custom_opts[c->custom_opts_count].str, > sizeof(c->custom_opts[0].str), > "%s", optarg)) > @@ -1503,7 +1511,15 @@ void conf(struct ctx *c, int argc, char **argv) > die("Too many --dhcp-opt entries (max %d)", > MAX_CUSTOM_DHCP_OPTS); > > + len = dhcp_opt_parse(optcode, comma + 1, > + c->custom_opts[c->custom_opts_count].val, > + sizeof(c->custom_opts[0].val)); > + if (len < 0) > + die("Invalid value for DHCP option %lu: %s", > + optcode, comma + 1); > + > c->custom_opts[c->custom_opts_count].code = optcode; > + c->custom_opts[c->custom_opts_count].len = len; > if (snprintf_check(c->custom_opts[c->custom_opts_count].str, > sizeof(c->custom_opts[0].str), > "%s", comma + 1)) > diff --git a/dhcp.c b/dhcp.c > index 1ff8cba..e1c95ad 100644 > --- a/dhcp.c > +++ b/dhcp.c > @@ -33,6 +33,154 @@ > #include "log.h" > #include "dhcp.h" > > +/** > + * dhcp_opt_types - Maps option code to RFC 2132 value type, indexed by code > + */ > +static const enum dhcp_opt_type dhcp_opt_types[256] = { > + [1] = DHCP_OPT_IPV4, /* Subnet Mask */ > + [2] = DHCP_OPT_INTEGER, /* Time Offset */ > + [3] = DHCP_OPT_IPV4_LIST, /* Router */ > + [4] = DHCP_OPT_IPV4_LIST, /* Time Server */ > + [5] = DHCP_OPT_IPV4_LIST, /* Name Server */ > + [6] = DHCP_OPT_IPV4_LIST, /* Domain Name Server */ > + [7] = DHCP_OPT_IPV4_LIST, /* Log Server */ > + [8] = DHCP_OPT_IPV4_LIST, /* Cookie Server */ > + [9] = DHCP_OPT_IPV4_LIST, /* LPR Server */ > + [10] = DHCP_OPT_IPV4_LIST, /* Impress Server */ > + [11] = DHCP_OPT_IPV4_LIST, /* Resource Location Server */ > + [12] = DHCP_OPT_STR, /* Host Name */ > + [13] = DHCP_OPT_INTEGER, /* Boot File Size */ > + [15] = DHCP_OPT_STR, /* Domain Name */ > + [16] = DHCP_OPT_IPV4, /* Swap Server */ > + [17] = DHCP_OPT_STR, /* Root Path */ > + [19] = DHCP_OPT_INTEGER, /* IP Forwarding */ > + [23] = DHCP_OPT_INTEGER, /* Default IP TTL */ > + [26] = DHCP_OPT_INTEGER, /* Interface MTU */ > + [28] = DHCP_OPT_IPV4, /* Broadcast Address */ > + [33] = DHCP_OPT_IPV4_LIST, /* Static Routes */ > + [37] = DHCP_OPT_INTEGER, /* TCP Default TTL */ > + [38] = DHCP_OPT_INTEGER, /* TCP Keepalive Interval */ > + [40] = DHCP_OPT_STR, /* NIS Domain Name */ > + [41] = DHCP_OPT_IPV4_LIST, /* NIS Servers */ > + [42] = DHCP_OPT_IPV4_LIST, /* NTP Servers */ > + [44] = DHCP_OPT_IPV4_LIST, /* NetBIOS Name Server */ > + [50] = DHCP_OPT_IPV4, /* Requested IP Address */ > + [51] = DHCP_OPT_INTEGER, /* IP Address Lease Time */ > + [53] = DHCP_OPT_INTEGER, /* DHCP Message Type */ > + [54] = DHCP_OPT_IPV4, /* Server Identifier */ > + [55] = DHCP_OPT_STR, /* Parameter Request List */ > + [57] = DHCP_OPT_INTEGER, /* Max DHCP Message Size */ > + [58] = DHCP_OPT_INTEGER, /* Renewal (T1) Time */ > + [59] = DHCP_OPT_INTEGER, /* Rebinding (T2) Time */ > + [60] = DHCP_OPT_STR, /* Vendor Class Identifier */ > + [61] = DHCP_OPT_STR, /* Client Identifier */ > + [66] = DHCP_OPT_STR, /* TFTP Server Name */ > + [67] = DHCP_OPT_STR, /* Bootfile Name */ > + [119] = DHCP_OPT_STR, /* Domain Search List */ > + [252] = DHCP_OPT_STR, /* WPAD URL */ > +}; > + > +/** > + * dhcp_opt_int_width - Integer width in bytes for INTEGER-typed options > + */ > +static const uint8_t dhcp_opt_int_width[256] = { I know I suggested this approach, but now seeing a whole array[256] it seems unpleasantly bulky. I'd suggest instead encoding the width into some bits of the DHCP_OPT_* constants. > + [2] = 4, /* Time Offset */ > + [13] = 2, /* Boot File Size */ > + [19] = 1, /* IP Forwarding */ > + [23] = 1, /* Default IP TTL */ > + [26] = 2, /* Interface MTU */ > + [37] = 1, /* TCP Default TTL */ > + [38] = 4, /* TCP Keepalive Interval */ > + [51] = 4, /* IP Address Lease Time */ > + [53] = 1, /* DHCP Message Type */ > + [57] = 2, /* Max DHCP Message Size */ > + [58] = 4, /* Renewal (T1) Time */ > + [59] = 4, /* Rebinding (T2) Time */ > +}; > + > +#define DHCP_OPT_PARSE_BUF 1024 > + > +/** > + * dhcp_opt_parse() - Parse a DHCP option value > + * @code: DHCP option code > + * @str: DHCP Value string from command line > + * @buf: Output buffer > + * @buf_len: Size of output buffer > + * > + * Return: number of bytes written to @buf, or -1 on error > + */ > +int dhcp_opt_parse(uint8_t code, const char *str, uint8_t *buf, size_t buf_len) > +{ > + enum dhcp_opt_type type = dhcp_opt_types[code]; > + char tmp[DHCP_OPT_PARSE_BUF]; > + char *tok, *saveptr, *end; > + struct in_addr addr; > + unsigned long val; > + unsigned int i; > + uint8_t width; > + size_t slen; > + int len; > + > + switch (type) { > + case DHCP_OPT_NONE: > + die("Unsupported DHCP option: %u," > + " see passt(1) for supported codes", code); > + case DHCP_OPT_IPV4: > + if (inet_pton(AF_INET, str, &addr) != 1) > + return -1; > + > + if (buf_len < sizeof(addr)) > + return -1; > + > + memcpy(buf, &addr, sizeof(addr)); > + > + return sizeof(addr); > + case DHCP_OPT_IPV4_LIST: I think it should be possible to share more logic between the single IPv4 and IPv4 list options (parse them both as a list, but error if there's >1 in the single case). > + len = 0; > + > + if (snprintf_check(tmp, sizeof(tmp), "%s", str)) > + return -1; > + > + for (tok = strtok_r(tmp, ",", &saveptr); tok; > + tok = strtok_r(NULL, ",", &saveptr)) { > + if (inet_pton(AF_INET, tok, &addr) != 1) > + return -1; > + > + if (len + (int)sizeof(addr) > (int)buf_len) > + return -1; > + > + memcpy(buf + len, &addr, sizeof(addr)); > + len += sizeof(addr); > + } > + return len; > + case DHCP_OPT_INTEGER: > + width = dhcp_opt_int_width[code]; > + val = strtoul(str, &end, 0); Most strtoul() errors can be discerned by checking end, but not all. You also need to explicitly set errno to 0 beforehand and check it again afterwards (clunky, but that's the interface we have). > + > + if (*end || buf_len < width) > + return -1; > + > + if (width < 4 && val >= (1UL << (width * 8))) strtoul() will parse 64-bit values on most current platforms, so you need this range enforcement for width==4 as well. > + return -1; > + > + for (i = 0; i < width; i++) > + buf[i] = (val >> ((width - 1 - i) * 8)) & 0xff; Might be easier to follow as: for (...) { buf[i] = val & 0xff; val >>= 8; } > + > + return width; > + case DHCP_OPT_STR: > + slen = strlen(str); > + > + if (!slen || slen >= buf_len) > + return -1; > + > + strncpy((char *)buf, str, buf_len); You've already know the length so you can make this a memcpy(). > + > + return slen; > + } > + > + return -1; > +} > + > /** > * struct opt - DHCP option > * @sent: Convenience flag, set while filling replies > diff --git a/dhcp.h b/dhcp.h > index cd50c99..3da571c 100644 > --- a/dhcp.h > +++ b/dhcp.h > @@ -6,7 +6,24 @@ > #ifndef DHCP_H > #define DHCP_H > > +/** > + * enum dhcp_opt_type - DHCP option value types per RFC 2132 > + * @DHCP_OPT_NONE: Unsupported or unknown option > + * @DHCP_OPT_STR: Variable-length string > + * @DHCP_OPT_IPV4: Single IPv4 address > + * @DHCP_OPT_IPV4_LIST:Multiple IPv4 addresses, comma-separated > + * @DHCP_OPT_INTEGER: Unsigned integer (1, 2, or 4 bytes) > + */ > +enum dhcp_opt_type { > + DHCP_OPT_NONE, > + DHCP_OPT_STR, > + DHCP_OPT_IPV4, > + DHCP_OPT_IPV4_LIST, > + DHCP_OPT_INTEGER, > +}; This can move to dhcp.c, since it's not used in any other files. > + > int dhcp(const struct ctx *c, struct iov_tail *data); > void dhcp_init(void); > +int dhcp_opt_parse(uint8_t code, const char *str, uint8_t *buf, size_t buf_len); > > #endif /* DHCP_H */ > diff --git a/passt.h b/passt.h > index 3a0816f..751fee3 100644 > --- a/passt.h > +++ b/passt.h > @@ -184,6 +184,8 @@ struct ip6_ctx { > * @fqdn: Guest FQDN > * @custom_opts: User-specified DHCP options from --dhcp-opt > * @custom_opts.code: DHCP option code > + * @custom_opts.len: Length of binary value in @val > + * @custom_opts.val: Binary-encoded option value > * @custom_opts.str: Original string value from command line > * @custom_opts_count: Number of entries in @custom_opts > * @ifi6: Template interface for IPv6, -1: none, 0: IPv6 disabled > @@ -271,6 +273,8 @@ struct ctx { > > struct { > uint8_t code; > + uint8_t len; > + uint8_t val[255]; > char str[256]; > } custom_opts[MAX_CUSTOM_DHCP_OPTS]; > int custom_opts_count; > -- > 2.54.0 > -- David Gibson (he or they) | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you, not the other way | around. http://www.ozlabs.org/~dgibson