Re: [PATCH v5 16/29] dhcpv6: Use iov_tail in dhcpv6_opt()

[Stefano Brivio <sbrivio@redhat.com>]

On Thu, 17 Apr 2025 18:51:23 +0200
Laurent Vivier <lvivier@redhat.com> wrote:

> Signed-off-by: Laurent Vivier <lvivier@redhat.com>
> ---
>  dhcpv6.c | 179 ++++++++++++++++++++++++++++++++-----------------------
>  iov.c    |   1 -
>  2 files changed, 103 insertions(+), 77 deletions(-)
> 
> diff --git a/dhcpv6.c b/dhcpv6.c
> index a52af1b7a0fe..365b609addda 100644
> --- a/dhcpv6.c
> +++ b/dhcpv6.c
> @@ -278,112 +278,122 @@ static struct resp_not_on_link_t {
>  
>  /**
>   * dhcpv6_opt() - Get option from DHCPv6 message
> - * @p:		Packet pool, single packet with UDP header
> - * @offset:	Offset to look at, 0: end of header, set to option start
> + * @data:	Data to look at (input/output)

This isn't really clear to me. I'd rather say it's data where we look
for options, and that it's set to the option on return, maybe:

 @data:		Buffer with options, set to matching option on return

?

>   * @type:	Option type to look up, network order
>   *
> - * Return: pointer to option header, or NULL on malformed or missing option
> + * Return: true if found and @data points to the option header,
> + *         or false on malformed or missing option and @data is
> + *         unmodified.
>   */
> -static struct opt_hdr *dhcpv6_opt(const struct pool *p, size_t *offset,
> -				  uint16_t type)
> +static bool dhcpv6_opt(struct iov_tail *data, uint16_t type)
>  {
> -	struct opt_hdr *o;
> -	size_t left;
> +	struct iov_tail head = *data;
> +	const struct opt_hdr *o;
> +	struct opt_hdr oc;
>  
> -	ASSERT(*offset >= UDP_MSG_HDR_SIZE);
> -
> -	while ((o = packet_get_try(p, 0, *offset, sizeof(*o), &left))) {
> +	while ((o = IOV_PEEK_HEADER(data, oc))) {
>  		unsigned int opt_len = ntohs(o->l) + sizeof(*o);
>  
> -		if (ntohs(o->l) > left)
> -			return NULL;
> +		if (opt_len > iov_tail_size(data))
> +			break;
>  
>  		if (o->t == type)
> -			return o;
> +			return true;
>  
> -		*offset += opt_len;
> +		iov_tail_drop(data, opt_len);
>  	}
>  
> -	return NULL;
> +	*data = head;
> +	return false;
>  }
>  
>  /**
>   * dhcpv6_ia_notonlink() - Check if any IA contains non-appropriate addresses
> - * @p:		Packet pool, single packet starting from UDP header
> + * @data:	Data to look at, packet starting from UDP header (input/output)
>   * @la:		Address we want to lease to the client
>   *
> - * Return: pointer to non-appropriate IA_NA or IA_TA, if any, NULL otherwise
> + * Return: true and @data points to non-appropriate IA_NA or IA_TA, if any,
> + *         false otherwise and @data is unmodified
>   */
> -static struct opt_hdr *dhcpv6_ia_notonlink(const struct pool *p,
> -					   struct in6_addr *la)
> +static bool dhcpv6_ia_notonlink(struct iov_tail *data,
> +				struct in6_addr *la)
>  {
>  	int ia_types[2] = { OPT_IA_NA, OPT_IA_TA }, *ia_type;
>  	const struct opt_ia_addr *opt_addr;
> +	struct iov_tail current, ia_base;
> +	struct opt_ia_addr opt_addrc;
>  	char buf[INET6_ADDRSTRLEN];
> +	const struct opt_ia_na *ia;
>  	struct in6_addr req_addr;
>  	const struct opt_hdr *h;
> -	struct opt_hdr *ia;
> -	size_t offset;
> +	struct opt_ia_na iac;
> +	struct opt_hdr hc;
>  
>  	foreach(ia_type, ia_types) {
> -		offset = UDP_MSG_HDR_SIZE;
> -		while ((ia = dhcpv6_opt(p, &offset, *ia_type))) {
> -			if (ntohs(ia->l) < OPT_VSIZE(ia_na))
> -				return NULL;
> -
> -			offset += sizeof(struct opt_ia_na);
> -
> -			while ((h = dhcpv6_opt(p, &offset, OPT_IAAADR))) {
> -				if (ntohs(h->l) != OPT_VSIZE(ia_addr))
> -					return NULL;
> -
> -				opt_addr = (const struct opt_ia_addr *)h;
> +		current = *data;
> +		while (dhcpv6_opt(&current, *ia_type)) {
> +			ia_base = current;
> +			ia = IOV_REMOVE_HEADER(&current, iac);
> +			if (!ia || ntohs(ia->hdr.l) < OPT_VSIZE(ia_na))
> +				goto notfound;
> +
> +			while (dhcpv6_opt(&current, OPT_IAAADR)) {
> +				h = IOV_PEEK_HEADER(&current, hc);
> +				if (!h || ntohs(h->l) != OPT_VSIZE(ia_addr))
> +					goto notfound;
> +
> +				opt_addr = IOV_REMOVE_HEADER(&current,
> +							     opt_addrc);
>  				req_addr = opt_addr->addr;
>  				if (!IN6_ARE_ADDR_EQUAL(la, &req_addr))
> -					goto err;
> -
> -				offset += sizeof(struct opt_ia_addr);
> +					goto notonlink;
>  			}
>  		}
>  	}
>  
> -	return NULL;
> +notfound:
> +	return false;
>  
> -err:
> +notonlink:
>  	info("DHCPv6: requested address %s not on link",
>  	     inet_ntop(AF_INET6, &req_addr, buf, sizeof(buf)));
> -	return ia;
> +	*data = ia_base;
> +	return true;
>  }
>  
>  /**
>   * dhcpv6_send_ia_notonlink() - Send NotOnLink status
> - * @c:		Execution context
> - * @ia:		Pointer to non-appropriate IA_NA or IA_TA
> - * @client_id:	Client ID message option
> - * xid:		Transaction ID for message exchange
> + * @c:			Execution context
> + * @ia_base:		Non-appropriate IA_NA or IA_TA base
> + * @client_id_base:	Client ID message option base
> + * @len:		Client ID length
> + * @xid:		Transaction ID for message exchange
>   */
> -static void dhcpv6_send_ia_notonlink(struct ctx *c, struct opt_hdr *ia,
> -				     const struct opt_hdr *client_id,
> -				     uint32_t xid)
> +static void dhcpv6_send_ia_notonlink(struct ctx *c,
> +				     const struct iov_tail *ia_base,
> +				     const struct iov_tail *client_id_base,
> +				     int len, uint32_t xid)
>  {
>  	const struct in6_addr *src = &c->ip6.our_tap_ll;
> +	struct opt_hdr *ia = (struct opt_hdr *)resp_not_on_link.var;
>  	size_t n;
>  
>  	info("DHCPv6: received CONFIRM with inappropriate IA,"
>  	     " sending NotOnLink status in REPLY");
>  
> -	ia->l = htons(OPT_VSIZE(ia_na) + sizeof(sc_not_on_link));
> -
>  	n = sizeof(struct opt_ia_na);
> -	memcpy(resp_not_on_link.var, ia, n);
> +	iov_to_buf(&ia_base->iov[0], ia_base->cnt, ia_base->off,
> +		   resp_not_on_link.var, n);
> +	ia->l = htons(OPT_VSIZE(ia_na) + sizeof(sc_not_on_link));
>  	memcpy(resp_not_on_link.var + n, &sc_not_on_link,
>  	       sizeof(sc_not_on_link));
>  
>  	n += sizeof(sc_not_on_link);
> -	memcpy(resp_not_on_link.var + n, client_id,
> -	       sizeof(struct opt_hdr) + ntohs(client_id->l));
> +	iov_to_buf(&client_id_base->iov[0], client_id_base->cnt,
> +		   client_id_base->off, resp_not_on_link.var + n,
> +		   sizeof(struct opt_hdr) + len);
>  
> -	n += sizeof(struct opt_hdr) + ntohs(client_id->l);
> +	n += sizeof(struct opt_hdr) + len;
>  
>  	n = offsetof(struct resp_not_on_link_t, var) + n;
>  
> @@ -472,17 +482,19 @@ search:
>  
>  /**
>   * dhcpv6_client_fqdn_fill() - Fill in client FQDN option
> + * @data:	Data to look at
>   * @c:		Execution context
>   * @buf:	Response message buffer where options will be appended
>   * @offset:	Offset in message buffer for new options
>   *
>   * Return: updated length of response message buffer.
>   */
> -static size_t dhcpv6_client_fqdn_fill(const struct pool *p, const struct ctx *c,
> +static size_t dhcpv6_client_fqdn_fill(const struct iov_tail *data,
> +				      const struct ctx *c,
>  				      char *buf, int offset)
>  
>  {
> -	struct opt_client_fqdn const *req_opt;
> +	struct iov_tail current = *data;
>  	struct opt_client_fqdn *o;
>  	size_t opt_len;
>  
> @@ -501,13 +513,16 @@ static size_t dhcpv6_client_fqdn_fill(const struct pool *p, const struct ctx *c,
>  
>  	o = (struct opt_client_fqdn *)(buf + offset);
>  	encode_domain_name(o->domain_name, c->fqdn);
> -	req_opt = (struct opt_client_fqdn *)dhcpv6_opt(p,
> -						&(size_t){ UDP_MSG_HDR_SIZE },
> -						OPT_CLIENT_FQDN);
> -	if (req_opt && req_opt->flags & 0x01 /* S flag */)
> -		o->flags = 0x02 /* O flag */;
> -	else
> -		o->flags = 0x00;
> +	if (dhcpv6_opt(&current, OPT_CLIENT_FQDN)) {
> +		struct opt_client_fqdn const *req_opt;
> +		struct opt_client_fqdn req_optc;
> +
> +		req_opt = IOV_PEEK_HEADER(&current, req_optc);
> +		if (req_opt && req_opt->flags & 0x01 /* S flag */)
> +			o->flags = 0x02 /* O flag */;
> +		else
> +			o->flags = 0x00;
> +	}

Earlier, if we didn't find the option, we would set o->flags to 0x00.
Now we do nothing.

-- 
Stefano