Re: [PATCH v3 2/2] dhcpv6: Inject custom options into DHCPv6 replies

On 8/24/26 14:13, Anshu Kumari wrote:

Append user-specified options from --dhcpv6-opt to DHCPv6 reply messages. Options are read from the pre-parsed static storage populated by dhcpv6_set_opt() at startup, and skipped with a debug message if they exceed the available space.

Link: https://bugs.passt.top/show_bug.cgi?id=192 Signed-off-by: Anshu Kumari --- v3: - rename dhcpv6_custom_opts_fill() to dhcpv6_user_opts_fill(). - Iterate directly over the pre-parsed binary dhcpv6_user_opts[] array instead of re-parsing string values at reply time.

v2: - Updated dhcpv6_custom_opts_fill() to parse str at reply time using dhcpv6_opt_parse() instead of copying cached val/len. --- dhcpv6.c | 39 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 39 insertions(+)

Reviewed-by: Laurent Vivier but see below

diff --git a/dhcpv6.c b/dhcpv6.c index 3964dd9..041b589 100644 --- a/dhcpv6.c +++ b/dhcpv6.c @@ -865,6 +865,43 @@ static size_t dhcpv6_client_fqdn_fill(const struct iov_tail *data, return offset + sizeof(struct opt_hdr) + opt_len; }

+/** + * dhcpv6_user_opts_fill() - Append user-specified options to reply + * @buf: Response message buffer + * @offset: Current offset in buffer + * + * Return: updated offset after appending user options + */ +static size_t dhcpv6_user_opts_fill(char *buf, size_t offset) +{ + unsigned int i; + + for (i = 0; i < ARRAY_SIZE(dhcpv6_user_opts); i++) { + int vlen = dhcpv6_user_opts[i].len; + struct opt_hdr *hdr; + + if (!vlen) + continue; + + if (offset + sizeof(struct opt_hdr) + vlen > + OPT_MAX_SIZE) { + debug("DHCPv6: option %u doesn't fit," + " skipping", i);

Perhaps a warn() rather than a debug(), to inform user that something bad happens?

+ continue; + } + + hdr = (struct opt_hdr *)(buf + offset); + hdr->t = htons(i); + hdr->l = htons(vlen); + offset += sizeof(struct opt_hdr); + + memcpy(buf + offset, dhcpv6_user_opts[i].val, vlen); + offset += vlen; + } + + return offset; +} + /** * dhcpv6() - Check if this is a DHCPv6 message, reply as needed * @c: Execution context @@ -1003,6 +1040,8 @@ int dhcpv6(struct ctx *c, struct iov_tail *data, sizeof(struct opt_hdr) + ntohs(client_id->l); n = dhcpv6_dns_fill(c, (char *)&resp, n); n = dhcpv6_client_fqdn_fill(data, c, (char *)&resp, n); + n = dhcpv6_user_opts_fill((char *)&resp, n); + resp.hdr.xid = mh->xid;

tap_udp6_send(c, src, 547, saddr, 546, mh->xid, &resp, n);