Implement option splitting per RFC 3396 for options that may exceed
255 bytes. A concat_req[] lookup table marks options requiring
concatenation (currently option 81, Client FQDN per RFC 4702).
The opts[].s buffer is resized from 255 to OPT_CONCAT_MAX to
hold the maximum data that can be split across the options
field, file field, and sname field.
When a concatenation-requiring option does not fit as a single
option in any field, fill() calls fill_split() to split it across
fields in RFC 3396 order: options field first, then file, then
sname. Each split chunk is capped at 255 bytes per the DHCP
option length field limit.
Link: https://bugs.passt.top/show_bug.cgi?id=192
Signed-off-by: Anshu Kumari
---
v8:
- OPT_CONCAT_MAX comment fixed
- struct opt reordered
- "written" variable initialization fixed
- foreach_unsent_opt() used in split loop
v7:
- Capped each split chunk at 255 bytes:
chunk = MIN(MIN(remaining, avail), 255) to prevent
overflow in the uint8_t length field
- Replaced inline space calculation with a dry-run pass
via fill_split_areas()
- Moved OPT_MAX and OPT_CONCAT_MAX definitions above struct opt.
- Reordered struct opt fields to place s[OPT_CONCAT_MAX]
- Added dry_run parameter to fill_split()
v6:
- Merged v5 patches 6/7 and 7/7 into a single patch.
- Replaced DHCP_OPT_STR_CONCAT enum value and is_concat_opt()
helper with a concat_req[] boolean lookup table.
- Used MIN() macro instead of ternary for chunk size.
- Fixed space calculation to account for 2-byte code+length
overhead per chunk.
v5:
- New patch: implement option splitting per RFC 3396 for options exceeding 255 bytes
- Add DHCP_OPT_STR_CONCAT type, is_concat_opt(), fill_split() helpers
- Resize opts[].s from 255 to OPT_CONCAT_MAX (497) bytes
- Add /* fallthrough */ between DHCP_OPT_STR and DHCP_OPT_STR_CONCAT case
---
dhcp.c | 161 ++++++++++++++++++++++++++++++++++++++++++++++++++-------
1 file changed, 141 insertions(+), 20 deletions(-)
diff --git a/dhcp.c b/dhcp.c
index 04a6d389..84b86109 100644
--- a/dhcp.c
+++ b/dhcp.c
@@ -35,6 +35,18 @@
#include "dhcp.h"
#include "parse.h"
+#define OPT_MIN 60 /* RFC 951 */
+
+/* Total option size (excluding end option) is 576 (RFC 2131), minus
+ * offset of options (268), minus end option (1).
+ */
+#define OPT_MAX 307
+
+/* RFC 3396: maximum option data that can be split across options field,
+ * file field, and sname field.
+ */
+#define OPT_CONCAT_MAX (OPT_MAX - 2 + 64 - 2 + 128 - 2)
+
/**
* enum opt_conf - DHCP option configuration
* @OPT_UNSET: Option not configured
@@ -51,18 +63,18 @@ enum opt_conf {
* struct opt - DHCP option
* @sent: Convenience flag, set while filling replies
* @slen: Length of option defined for server
- * @s: Option payload from server
* @clen: Length of option received from client, -1 if not received
- * @c: Option payload from client
* @conf: Option configuration (unset, default, or user)
+ * @c: Option payload from client
+ * @s: Option payload from server
*/
struct opt {
int sent;
int slen;
- uint8_t s[255];
int clen;
- uint8_t c[255];
enum opt_conf conf;
+ uint8_t c[255];
+ uint8_t s[OPT_CONCAT_MAX];
};
static struct opt opts[256];
@@ -83,32 +95,23 @@ static struct opt opts[256];
#define DHCPINFORM 8
#define DHCPFORCERENEW 9
-#define OPT_MIN 60 /* RFC 951 */
-
-/* Total option size (excluding end option) is 576 (RFC 2131), minus
- * offset of options (268), minus end option (1).
- */
-#define OPT_MAX 307
-
/**
* dhcp_init() - Initialise DHCP options
*/
void dhcp_init(void)
{
if (opts[1].conf != OPT_USER) /* Mask */
- opts[1] = (struct opt) { 0, 4, { 0 }, 0, { 0 }, OPT_DEFAULT };
+ opts[1] = (struct opt) { 0, 4, 0, OPT_DEFAULT, { 0 }, { 0 } };
if (opts[3].conf != OPT_USER) /* Router */
- opts[3] = (struct opt) { 0, 4, { 0 }, 0, { 0 }, OPT_DEFAULT };
+ opts[3] = (struct opt) { 0, 4, 0, OPT_DEFAULT, { 0 }, { 0 } };
if (opts[51].conf != OPT_USER) { /* Lease time */
- opts[51] = (struct opt) { 0, 4, { 0xff, 0xff, 0xff, 0xff },
- 0, { 0 }, OPT_DEFAULT };
+ opts[51] = (struct opt) { 0, 4, 0, OPT_DEFAULT, { 0 },
+ { 0xff, 0xff, 0xff, 0xff } };
}
/* Type */
- opts[53] = (struct opt) { 0, 1, { 0 }, 0, { 0 }, OPT_DEFAULT };
- if (opts[54].conf != OPT_USER) { /* Server ID */
- opts[54] = (struct opt) { 0, 4, { 0 }, 0, { 0 },
- OPT_DEFAULT };
- }
+ opts[53] = (struct opt) { 0, 1, 0, OPT_DEFAULT, { 0 }, { 0 } };
+ if (opts[54].conf != OPT_USER) /* Server ID */
+ opts[54] = (struct opt) { 0, 4, 0, OPT_DEFAULT, { 0 }, { 0 } };
}
/**
@@ -215,6 +218,11 @@ static const enum dhcp_opt_type dhcp_opt_types[] = {
[252] = DHCP_OPT_STR, /* WPAD URL */
};
+/* Options requiring RFC 3396 concatenation, indexed by code */
+static const bool concat_req[256] = {
+ [81] = true, /* Client FQDN (RFC 4702, Section 2) */
+};
+
/**
* dhcp_opt_parse() - Parse a DHCP option value
* @code: DHCP option code
@@ -312,6 +320,9 @@ static int dhcp_opt_parse(uint8_t code, const char *str,
case DHCP_OPT_STR:
slen = strlen(str);
+ if (!concat_req[code] && slen > 255)
+ return -1;
+
if (slen > buf_len)
return -1;
@@ -446,6 +457,45 @@ static void fill_one(uint8_t *buf, size_t size, int o, int *offset)
*offset += slen;
}
+/**
+ * fill_split() - Write a split portion of an option into a buffer
+ * @buf: Buffer to write into
+ * @size: Usable size of @buf
+ * @o: Option number (code)
+ * @offset: Current offset within @buf, updated on write
+ * @data: Pointer to remaining option data to write
+ * @remaining: Bytes of option data still to write
+ * @dry_run: If true, calculate size without writing to @buf
+ *
+ * Return: number of data bytes written (excluding code+length header)
+ */
+static size_t fill_split(uint8_t *buf, size_t size, int o, int *offset,
+ const uint8_t *data, size_t remaining,
+ bool dry_run)
+{
+ size_t avail, chunk;
+
+ if (*offset + 2 >= (int)size)
+ return 0;
+
+ avail = size - *offset - 2;
+ chunk = MIN(MIN(remaining, avail), 255);
+ if (!chunk)
+ return 0;
+
+ if (!dry_run) {
+ buf[*offset] = o;
+ buf[*offset + 1] = chunk;
+ }
+ *offset += 2;
+
+ if (!dry_run)
+ memcpy(buf + *offset, data, chunk);
+ *offset += chunk;
+
+ return chunk;
+}
+
/**
* enum dhcp_overload - DHCP option overload values (RFC 2132, Section 9.3)
* @DHCP_OVERLOAD_NONE: No overload
@@ -458,6 +508,43 @@ enum dhcp_overload {
DHCP_OVERLOAD_SNAME = 2,
};
+/**
+ * fill_split_areas() - Write a split option across options, file, and sname areas
+ * @m: Message to write into
+ * @opt_size: Usable size of the options area
+ * @o: Option number (code)
+ * @opt_off: Current offset within options area, updated on write
+ * @file_off: Current offset within file area, updated on write
+ * @sname_off: Current offset within sname area, updated on write
+ * @has_bootfile: If true, skip the file field
+ * @dry_run: If true, calculate size without writing
+ *
+ * Return: total data bytes written across all areas
+ */
+static size_t fill_split_areas(struct msg *m, size_t opt_size, int o,
+ int *opt_off, int *file_off, int *sname_off,
+ bool has_bootfile, bool dry_run)
+{
+ size_t written;
+
+ written = fill_split(m->o, opt_size, o, opt_off,
+ opts[o].s, opts[o].slen, dry_run);
+ if (written < (size_t)opts[o].slen && !has_bootfile) {
+ written += fill_split(m->file, sizeof(m->file) - 1, o,
+ file_off,
+ opts[o].s + written,
+ opts[o].slen - written, dry_run);
+ }
+ if (written < (size_t)opts[o].slen) {
+ written += fill_split(m->sname, sizeof(m->sname) - 1, o,
+ sname_off,
+ opts[o].s + written,
+ opts[o].slen - written, dry_run);
+ }
+
+ return written;
+}
+
/**
* fill() - Fill options in message, with overload into file/sname if needed
* @m: Message to fill
@@ -503,6 +590,40 @@ static int fill(struct msg *m, bool has_bootfile)
fill_one(m->file, sizeof(m->file) - 1, o, &file_off);
}
+ /* RFC 3396: split concatenation-requiring options that didn't fit
+ * as a single option. Split order: options, file, sname.
+ */
+ foreach_unsent_opt(o) {
+ int dry_off, dry_file_off, dry_sname_off;
+ size_t total, written;
+
+ if (!concat_req[o])
+ continue;
+
+ /* Dry run: verify the option fits across all areas */
+ dry_off = offset;
+ dry_file_off = file_off;
+ dry_sname_off = sname_off;
+
+ total = fill_split_areas(m, size, o,
+ &dry_off, &dry_file_off,
+ &dry_sname_off,
+ has_bootfile, true);
+
+ if (total < (size_t)opts[o].slen) {
+ debug("DHCP: skipping option %i (no space)", o);
+ continue;
+ }
+
+ /* Actual write */
+ written = fill_split_areas(m, size, o,
+ &offset, &file_off, &sname_off,
+ has_bootfile, false);
+
+ if (written >= (size_t)opts[o].slen)
+ opts[o].sent = 1;
+ }
+
/* Report any options that could not be sent */
foreach_unsent_opt(o)
debug("DHCP: skipping option %i", o);
--
2.55.0