Re: [PATCH v3 3/6] dhcp: Add option type table and value parser

[David Gibson <david@gibson.dropbear.id.au>]

[-- Attachment #1: Type: text/plain, Size: 10921 bytes --]

On Fri, Jun 12, 2026 at 01:04:41AM +0200, Stefano Brivio wrote:
> On Mon,  1 Jun 2026 13:07:53 +0530
> Anshu Kumari <anskuma@redhat.com> 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 <anskuma@redhat.com>
> > ---
> > 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.
> > 
> > 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 <unistd.h>
> >  #include <string.h>
> >  #include <limits.h>
> > +#include <errno.h>
> >  
> >  #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 */
> > +	[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;
> > +
> > +		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);
> > +
> > +			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);
> > +
> > +		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));
> > +	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
> 
> But we already have struct opt opts[255] in dhcp.c, why don't you use
> that directly? It would have the advantage of clearly separating what
> belongs to the configuration proper and what belongs to the specific
> DHCP encoding.
> 
> Besides, I see the point in maintaining what was set via command line,
> but not some temporary value that would just be copied to struct opt[].
> This would be a third copy.

Right, that's what I was getting at :).

-- 
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

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]