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