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

[Anshu Kumari <anskuma@redhat.com>]

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
  * @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