On Mon, Jun 01, 2026 at 01:07:53PM +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 dhcp_add_option() 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 > --- > v3: > - Replaced DHCP_OPT_INTEGER with separate DHCP_OPT_INT8/INT16/INT32 > enums, removed dhcp_opt_int_width[] array. > - Shared logic between DHCP_OPT_IPV4 and DHCP_OPT_IPV4_LIST — parse > both as list, error if >1 in single case. > - Added errno = 0 before strtoul() and check after. > - Fixed range check: 1ULL << (width * 8) for all widths including > width==4. > - strncpy → memcpy for DHCP_OPT_STR. > - Moved enum to dhcp.c since not used in other files. > - Removed options 55, 61 (client-only), 119 (DNS compression, use > --dhcp-search instead), 33 (IP pairs not supported). > - DHCP_OPT_PARSE_BUF 1024 → char tmp[256]. > - Upgraded dhcp_add_option() to call dhcp_opt_parse() and populate > val[]/len. > - Aligned array entries for readability. > - Added tab after @DHCP_OPT_IPV4_LIST: in kerneldoc. > - Reject empty value strings before parsing > - Reject leading/trailing/consecutive commas in IP list values. Thanks for the detailed changelogs, by the way. I know these are a bunch of work to maintain, but they really help when reviewing. > 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. > --- > dhcp.c | 180 +++++++++++++++++++++++++++++++++++++++++++++++++++++++- > passt.h | 4 ++ > 2 files changed, 181 insertions(+), 3 deletions(-) > > diff --git a/dhcp.c b/dhcp.c > index c5fbf37..07a42b9 100644 > --- a/dhcp.c > +++ b/dhcp.c > @@ -23,6 +23,7 @@ > #include > #include > #include > +#include > > #include "util.h" > #include "ip.h" > @@ -33,6 +34,170 @@ > #include "log.h" > #include "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_INT8: Unsigned 8-bit integer > + * @DHCP_OPT_INT16: Unsigned 16-bit integer > + * @DHCP_OPT_INT32: Unsigned 32-bit integer > + */ > +enum dhcp_opt_type { > + DHCP_OPT_NONE, > + DHCP_OPT_STR, > + DHCP_OPT_IPV4, > + DHCP_OPT_IPV4_LIST, > + DHCP_OPT_INT8, > + DHCP_OPT_INT16, > + DHCP_OPT_INT32, > +}; > + > +/** > + * 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_INT32, /* Time Offset */ > + [3] = DHCP_OPT_IPV4_LIST, /* Router */ I'm still a bit unsure if we want to allow user modification of the options, like this one, which we already manage ourselves. > + [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_INT16, /* Boot File Size */ > + [15] = DHCP_OPT_STR, /* Domain Name */ > + [16] = DHCP_OPT_IPV4, /* Swap Server */ > + [17] = DHCP_OPT_STR, /* Root Path */ > + [19] = DHCP_OPT_INT8, /* IP Forwarding */ > + [23] = DHCP_OPT_INT8, /* Default IP TTL */ > + [26] = DHCP_OPT_INT16, /* Interface MTU */ > + [28] = DHCP_OPT_IPV4, /* Broadcast Address */ > + [37] = DHCP_OPT_INT8, /* TCP Default TTL */ > + [38] = DHCP_OPT_INT32, /* 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_INT32, /* IP Address Lease Time */ > + [53] = DHCP_OPT_INT8, /* DHCP Message Type */ > + [54] = DHCP_OPT_IPV4, /* Server Identifier */ > + [57] = DHCP_OPT_INT16, /* Max DHCP Message Size */ > + [58] = DHCP_OPT_INT32, /* Renewal (T1) Time */ > + [59] = DHCP_OPT_INT32, /* Rebinding (T2) Time */ > + [60] = DHCP_OPT_STR, /* Vendor Class Identifier */ > + [66] = DHCP_OPT_STR, /* TFTP Server Name */ > + [67] = DHCP_OPT_STR, /* Bootfile Name */ > + [252] = DHCP_OPT_STR, /* WPAD URL */ > +}; > + > +/** > + * dhcp_opt_parse() - Parse a DHCP option value > + * @code: DHCP 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 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 *tok, *saveptr, *end; > + struct in_addr addr; > + unsigned long val; > + unsigned int i; > + uint8_t width; > + char tmp[256]; > + size_t slen; > + int len; > + > + if (!*str) > + die("Empty value for DHCP option %u", code); > + > + switch (type) { > + case DHCP_OPT_NONE: > + die("Unsupported DHCP option: %u," > + " see passt(1) for supported codes", code); > + case DHCP_OPT_IPV4: > + case DHCP_OPT_IPV4_LIST: > + len = 0; > + > + /* Reject empty, leading/trailing, or consecutive commas */ > + if (!*str || *str == ',' || str[strlen(str) - 1] == ',' || > + strstr(str, ",,")) > + return -1; > + > + if (snprintf_check(tmp, sizeof(tmp), "%s", str)) > + return -1; The arbitrary 256 byte buffer limit here isn't great. The string encoding of an IPv4 address can be nearly 4 times as long as the binary encoding, so we could potentially hit this with a longish, but not ridiculous address list. > + for (tok = strtok_r(tmp, ",", &saveptr); tok; > + tok = strtok_r(NULL, ",", &saveptr)) { One way to avoid that would be to avoid using strtok_r() which relies in in-place modifying the input. Instead you'd need to repeatedly find the length of the next chunk with strchr() or strcpsn(), then extract each one into a tmp of length INET_ADDRSTRLEN to call inet_pton(). On the plus side, that should naturally deal with the case of extraneous commas (it would show up as an empth entry), rather than requiring an explicit check at the top. > + if (inet_pton(AF_INET, tok, &addr) != 1) > + return -1; > + > + if (len + (int)sizeof(addr) > (int)buf_len) > + return -1; You could make this check before the inet_pton(), then do the conversion directly into buf, avoiding the addr temporary. > + > + memcpy(buf + len, &addr, sizeof(addr)); > + len += sizeof(addr); > + > + if (type == DHCP_OPT_IPV4) > + break; > + } > + > + if (type == DHCP_OPT_IPV4 && strtok_r(NULL, ",", &saveptr)) > + return -1; > + > + return len; > + case DHCP_OPT_INT8: > + case DHCP_OPT_INT16: > + case DHCP_OPT_INT32: > + if (type == DHCP_OPT_INT8) > + width = 1; > + else if (type == DHCP_OPT_INT16) > + width = 2; > + else > + width = 4; > + > + errno = 0; > + val = strtoul(str, &end, 0); > + > + if (*end || errno) > + return -1; > + > + if (buf_len < width) > + return -1; > + > + if (val >= (1ULL << (width * 8))) > + return -1; > + > + for (i = width; i > 0; i--) { > + buf[i - 1] = val & 0xff; > + val >>= 8; > + } > + > + return width; > + case DHCP_OPT_STR: > + slen = strlen(str); > + > + if (!slen || slen >= buf_len) > + return -1; > + > + memcpy(buf, str, slen); Do you need to include the terminating \0 here? If so you'll need slen + 1. > + > + return slen; > + } > + > + return -1; > +} > > /** > * dhcp_add_option() - Add or update a custom DHCP option > @@ -40,14 +205,15 @@ > * @code: DHCP option code > * @val_str: Value string from command line > * > - * If @code was already added, the previous value is overwritten. > - * Calls die() on any error. > + * Parses @val_str according to the type registered for @code in > + * dhcp_opt_types[]. If @code was already added, the previous value > + * is overwritten. Calls die() on any error. > * > * Return: 0 on success > */ > int dhcp_add_option(struct ctx *c, uint8_t code, const char *val_str) > { > - int idx; > + int idx, ret; > > for (idx = 0; idx < c->custom_opts_count; idx++) { > if (c->custom_opts[idx].code == code) > @@ -61,7 +227,15 @@ int dhcp_add_option(struct ctx *c, uint8_t code, const char *val_str) > c->custom_opts_count++; > } > > + ret = dhcp_opt_parse(code, val_str, > + c->custom_opts[idx].val, > + sizeof(c->custom_opts[0].val)); Now that this parsing and adding code is all in dhcp.c, could we parse the options directly into the existing opts[] global, rather than requiring both the string and parsed forms in c->custom_opts? > + if (ret < 0) > + die("Invalid value for DHCP option %u: %s", > + code, val_str); > + > c->custom_opts[idx].code = code; > + c->custom_opts[idx].len = ret; > > if (snprintf_check(c->custom_opts[idx].str, > sizeof(c->custom_opts[0].str), > 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