Re: [PATCH 3/6] dhcp: Add option type table and value parser

On Mon, May 18, 2026 at 06:49:59PM +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 --- conf.c | 9 +++ dhcp.c | 227 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++ dhcp.h | 15 ++++ 3 files changed, 251 insertions(+)

diff --git a/conf.c b/conf.c index 61a393f..3ec10ac 100644 --- a/conf.c +++ b/conf.c @@ -1485,6 +1485,7 @@ void conf(struct ctx *c, int argc, char **argv) unsigned long code; const char *comma; char *end; + int len;

comma = strchr(optarg, ','); if (!comma) @@ -1499,7 +1500,15 @@ 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(code, 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", + code, comma + 1); + c->custom_opts[c->custom_opts_count].code = code; + c->custom_opts[c->custom_opts_count].len = len;

I don't love the fact that .val and .str permanently store redundant information. Initially I was going to suggest that you delay dhcp_opt_parse() until you're actually processing a DHCP message. However, that's also not great at that point it awkward to handle parse errors. Not sure how best to tackle this for now.

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..9220516 100644 --- a/dhcp.c +++ b/dhcp.c @@ -33,6 +33,233 @@ #include "log.h" #include "dhcp.h"

+/** + * struct dhcp_opt_type_entry - Maps option code to RFC 2132 value type + * @code: DHCP option code + * @type: Expected value format + */ +static const struct dhcp_opt_type_entry { + uint8_t code; + enum dhcp_opt_type type; +} dhcp_opt_types[] = { + { 1, DHCP_OPT_IPV4 }, /* Subnet Mask */ + { 2, DHCP_OPT_UINT32 }, /* 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_UINT16 }, /* Boot File Size */ + { 15, DHCP_OPT_STR }, /* Domain Name */ + { 16, DHCP_OPT_IPV4 }, /* Swap Server */ + + { 17, DHCP_OPT_STR }, /* Root Path */ + { 19, DHCP_OPT_UINT8 }, /* IP Forwarding */ + { 23, DHCP_OPT_UINT8 }, /* Default IP TTL */ + { 26, DHCP_OPT_UINT16 }, /* Interface MTU */ + { 28, DHCP_OPT_IPV4 }, /* Broadcast Address */ + + { 33, DHCP_OPT_IPV4_LIST }, /* Static Routes (dest+router pairs) */ + { 37, DHCP_OPT_UINT8 }, /* TCP Default TTL */ + { 38, DHCP_OPT_UINT32 }, /* 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_UINT32 }, /* IP Address Lease Time */ + { 53, DHCP_OPT_UINT8 }, /* DHCP Message Type */ + + { 54, DHCP_OPT_IPV4 }, /* Server Identifier */ + { 57, DHCP_OPT_UINT16 }, /* Max DHCP Message Size */ + { 58, DHCP_OPT_UINT32 }, /* Renewal (T1) Time */ + { 59, DHCP_OPT_UINT32 }, /* 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 (RFC 3397) */ + { 121, DHCP_OPT_ROUTES }, /* Classless Static Routes */ + + { 252, DHCP_OPT_STR }, /* WPAD URL */

At least initially, I'd suggest we don't permit the user to set options which passt already manages internally (1, 3, 51, 53, 54, 55, and 199 from a quick scan).

+}; + +/** + * dhcp_opt_type_lookup() - Look up the value type for a DHCP option code + * @code: DHCP option code + * + * Return: type from table + */ +static enum dhcp_opt_type dhcp_opt_type_lookup(uint8_t code) +{ + unsigned int i; + + for (i = 0; i < ARRAY_SIZE(dhcp_opt_types); i++) { + if (dhcp_opt_types[i].code == code) + return dhcp_opt_types[i].type; + } + + return DHCP_OPT_NONE; +} + +/** + * dhcp_opt_parse() - Parse a DHCP option value + * @code: DHCP option code (determines value type via lookup table) + * @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 + */ +int dhcp_opt_parse(uint8_t code, const char *str, uint8_t *buf, size_t buf_len) +{ + enum dhcp_opt_type type = dhcp_opt_type_lookup(code); + + switch (type) { + case DHCP_OPT_NONE: { + die("Unsupported DHCP option: %u," + " see passt(1) for supported codes", + code); + } + case DHCP_OPT_IPV4: { + struct in_addr addr; + + 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: { + char *tok, *saveptr; + char tmp[1024];

Bare 1024 constant isn't ideal.

+ int len = 0; + + if (snprintf_check(tmp, sizeof(tmp), "%s", str)) + return -1; + + for (tok = strtok_r(tmp, " ", &saveptr); tok; + tok = strtok_r(NULL, " ", &saveptr)) {

Apparently strtok_r() is specified by POSIX, so it should be ok. Might be worth double checking musl has it, though. " " seems an odd choice of delimiter - it's pretty awkward to use on the command line. I guess "," is also problematic since it can be found within various of the of the option values.

+ struct in_addr addr; + + 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_UINT8: { + unsigned long val; + char *end; + + val = strtoul(str, &end, 0); + if (*end || val > 255 || buf_len < 1) + return -1; + buf[0] = val; + return 1; + } + case DHCP_OPT_UINT16: { + unsigned long val; + char *end; + + val = strtoul(str, &end, 0); + if (*end || val > 65535 || buf_len < 2) + return -1; + buf[0] = (val >> 8) & 0xff; + buf[1] = val & 0xff; + return 2; + } + case DHCP_OPT_UINT32: { + unsigned long val; + char *end; + + val = strtoul(str, &end, 0); + if (*end || buf_len < 4) + return -1; + buf[0] = (val >> 24) & 0xff; + buf[1] = (val >> 16) & 0xff; + buf[2] = (val >> 8) & 0xff; + buf[3] = val & 0xff; + return 4; + }

It might be possible to simplify the sections above using a single DHCP_OPT_INTEGER type, plus an extra field giving the integer width.

+ case DHCP_OPT_ROUTES: {

I'd consider excluding this one for now. For one thing it's rather a lot of code. But more importantly with the multi-address and route monitoring changes we're considering, there's a fairly high chance we might want to manage this one ourselves.

+ /* RFC 3442: "CIDR/mask,gateway" entries, space-separated + * Encodes as: mask-width + significant-octets + router + * e.g. "192.168.1.0/24,10.0.0.1 0.0.0.0/0,10.0.0.1" + */ + char *tok, *saveptr; + char tmp[1024]; + int len = 0; + + if (snprintf_check(tmp, sizeof(tmp), "%s", str)) + return -1; + + for (tok = strtok_r(tmp, " ", &saveptr); tok; + tok = strtok_r(NULL, " ", &saveptr)) { + struct in_addr dest, gw; + char *slash, *comma; + unsigned long mask; + int sig_octets; + + slash = strchr(tok, '/'); + if (!slash) + return -1; + *slash = '\0'; + + if (inet_pton(AF_INET, tok, &dest) != 1) + return -1; + + comma = strchr(slash + 1, ','); + if (!comma) + return -1; + *comma = '\0'; + + mask = strtoul(slash + 1, NULL, 10); + if (mask > 32) + return -1; + + if (inet_pton(AF_INET, comma + 1, &gw) != 1) + return -1; + + sig_octets = (mask + 7) / 8; + + if (len + 1 + sig_octets + 4 > (int)buf_len) + return -1; + + buf[len++] = mask; + memcpy(buf + len, &dest, sig_octets); + len += sig_octets; + memcpy(buf + len, &gw, 4); + len += 4; + } + return len; + } + case DHCP_OPT_STR: { + size_t len = strlen(str); + + if (!len || len >= buf_len) + return -1; + strncpy((char *)buf, str, buf_len); + return len; + } + } + + return -1; +} + /** * struct opt - DHCP option * @sent: Convenience flag, set while filling replies diff --git a/dhcp.h b/dhcp.h index cd50c99..01b2290 100644 --- a/dhcp.h +++ b/dhcp.h @@ -6,7 +6,22 @@ #ifndef DHCP_H #define DHCP_H

+/** + * enum dhcp_opt_type - DHCP option value types per RFC 2132 + */ +enum dhcp_opt_type { + DHCP_OPT_NONE, + DHCP_OPT_STR, + DHCP_OPT_IPV4, + DHCP_OPT_IPV4_LIST, + DHCP_OPT_UINT8, + DHCP_OPT_UINT16, + DHCP_OPT_UINT32, + DHCP_OPT_ROUTES, +}; + 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 */ -- 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