Re: [PATCH v2 3/6] dhcp: Add option type table and value parser

[Anshu Kumari <anskuma@redhat.com>]

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On Tue, May 26, 2026 at 9:35 PM Laurent Vivier <lvivier@redhat.com> wrote:

> On 5/26/26 14:31, 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 <anskuma@redhat.com>
> > ---
> > 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;
>
> I think you don't need to introduce len for --dhcp-opt as you already use
> ret for --dhcp-boot
> >
> >
> >       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));
>
> you can use "ret" here too
>
> > +                     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 */
>
> This is a client option, I don't think we need to manage it.
>
> > +     [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 */
>
> This is also a client option.
>
> > +     [66] = DHCP_OPT_STR,            /* TFTP Server Name */
> > +     [67] = DHCP_OPT_STR,            /* Bootfile Name */
> > +     [119] = DHCP_OPT_STR,           /* Domain Search List */
>
> This is not really a string as this uses the message compression described
> in RFC 1035,
> 4.1.4. (See also 3. Example in rfc3397). I'm not sure we can encode this
> manually on the
> command line. And RFC 3396 defines how to encode search string for more
> than 255
> characters length
>
> > +     [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] = {
> > +     [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
>
> Do we need 1024 bytes, all options are bounded to 256 bytes.
> > +
> > +/**
> > + * 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:
> > +             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);
> > +
> > +             if (*end || buf_len < width)
> > +                     return -1;
> > +
> > +             if (width < 4 && val >= (1UL << (width * 8)))
> > +                     return -1;
> > +
> > +             for (i = 0; i < width; i++)
> > +                     buf[i] = (val >> ((width - 1 - i) * 8)) & 0xff;
> > +
> > +             return width;
> > +     case DHCP_OPT_STR:
> > +             slen = strlen(str);
> > +
> > +             if (!slen || slen >= buf_len)
> > +                     return -1;
> > +
> > +             strncpy((char *)buf, str, buf_len);
> > +
> > +             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,
> > +};
> > +
> >   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];
>
> Why do we need to keep str[] once the value is encoded into val[]?
>

To print the option value as entered by user.


anskuma@anskuma-thinkpadp1gen7:~/Documents/passt$ ./passt -f   --dhcp-opt
60,HTTPClient --dhcp-opt 67,http://192.168.1.1:8080/alpine.iso --dhcp-opt
12,testhost   --dhcp-opt 15,test.example.com   --dhcp-opt 6,8.8.8.8,8.8.4.4
  --dhcp-opt 26,1400   --dhcp-opt 42,192.168.1.1   --dhcp-opt 51,360
--dhcp-opt 6,1.1.1.1,9.9.9.9
UNIX domain socket bound at /tmp/passt_1.socket
No IPv6 nameserver available for NDP/DHCPv6
Template interface: wlp9s0f0 (IPv4), wlp9s0f0 (IPv6)
MAC:
    host: 9a:55:9a:55:9a:55
    NAT to host 127.0.0.1: 192.168.1.1
DHCP:
    assign: 192.168.1.9
    mask: 255.255.255.0
    router: 192.168.1.1







*option 60: HTTPClient    option 67: http://192.168.1.1:8080/alpine.iso
<http://192.168.1.1:8080/alpine.iso>    option 12: testhost    option 15:
test.example.com <http://test.example.com>    option 6: 1.1.1.1,9.9.9.9
option 26: 1400    option 42: 192.168.1.1    option 51: 360*


>
> >       } custom_opts[MAX_CUSTOM_DHCP_OPTS];
> >       int custom_opts_count;
>
> Thanks,
> Laurent
>
>

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