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pping: Avoid timestamping pure TCP ACKs

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Add a parsing_context struct to keep track data, data_end and
currently parsed position, as well as handling the difference between
data_end for XDP and TC through data_end_end pointer.

Use parsing_context struct to detect pure TCP ACKs, and avoid creating
identifier for them on egress (to avoid creating timestamp
entries). This solves issue of calculating RTTs in inproper contexts.

Signed-off-by: Simon Sundberg <simon.sundberg@kau.se>
This commit is contained in:
Simon Sundberg
2021-02-12 18:31:30 +01:00
parent 502663f354
commit 219e962832
3 changed files with 41 additions and 18 deletions
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41
pping/pping_helpers.h
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@@ -18,6 +18,21 @@
#define AF_INET6 10
#define MAX_TCP_OPTIONS 10
/*
* This struct keeps track of the data and data_end pointers from the xdp_md or
* __skb_buff contexts, as well as a currently parsed to position kept in nh.
* The member data_end_end pointer which has the adress that would correspond
* to the logical end of the packet (for XDP, this is the same as data_end,
* but for TC this is skb->data + skb->len), which is useful for determining
* how much data a certain header encloses.
*/
struct parsing_context {
void *data; //Start of eth hdr
void *data_end; //End of safe acessible area
void *data_end_end; //Logical end of packet
struct hdr_cursor nh; //Position to parse next
};
/*
* Maps and IPv4 address into an IPv6 address according to RFC 4291 sec 2.5.5.2
*/
@@ -85,18 +100,21 @@ static int parse_tcp_ts(struct tcphdr *tcph, void *data_end, __u32 *tsval,
* and dest, respectively, and 0 will be returned. On failure, -1 will be
* returned.
*/
// Has 6 parameters (one too many)
static int parse_tcp_identifier(struct hdr_cursor *nh, void *data_end,
bool is_egress, struct flow_address *saddr,
static int parse_tcp_identifier(struct parsing_context *ctx, bool is_egress,
struct flow_address *saddr,
struct flow_address *daddr, __u32 *identifier)
{
__u32 tsval, tsecr;
struct tcphdr *tcph;
if (parse_tcphdr(nh, data_end, &tcph) < 0)
if (parse_tcphdr(&ctx->nh, ctx->data_end, &tcph) < 0)
return -1;
if (parse_tcp_ts(tcph, data_end, &tsval, &tsecr) < 0)
// Do not timestamp pure ACKs
if (is_egress && ctx->data_end_end <= ctx->nh.pos && !tcph->syn)
return -1;
if (parse_tcp_ts(tcph, ctx->data_end, &tsval, &tsecr) < 0)
return -1; //Possible TODO, fall back on seq/ack instead
saddr->port = tcph->source;
@@ -116,11 +134,10 @@ static int parse_tcp_identifier(struct hdr_cursor *nh, void *data_end,
* destination and source of packet, respectively), and identifier will be
* set to the identifier of a response.
*/
static int parse_packet_identifier(void *data, void *data_end, bool is_egress,
static int parse_packet_identifier(struct parsing_context *ctx, bool is_egress,
struct packet_id *p_id)
{
int proto, err;
struct hdr_cursor nh = { .pos = data };
struct ethhdr *eth;
struct iphdr *iph;
struct ipv6hdr *ip6h;
@@ -135,23 +152,23 @@ static int parse_packet_identifier(void *data, void *data_end, bool is_egress,
daddr = &p_id->flow.saddr;
}
proto = parse_ethhdr(&nh, data_end, &eth);
proto = parse_ethhdr(&ctx->nh, ctx->data_end, &eth);
// Parse IPv4/6 header
if (proto == bpf_htons(ETH_P_IP)) {
p_id->flow.ipv = AF_INET;
proto = parse_iphdr(&nh, data_end, &iph);
proto = parse_iphdr(&ctx->nh, ctx->data_end, &iph);
} else if (proto == bpf_htons(ETH_P_IPV6)) {
p_id->flow.ipv = AF_INET6;
proto = parse_ip6hdr(&nh, data_end, &ip6h);
proto = parse_ip6hdr(&ctx->nh, ctx->data_end, &ip6h);
} else {
return -1;
}
// Add new protocols here
if (proto == IPPROTO_TCP) {
err = parse_tcp_identifier(&nh, data_end, is_egress, saddr,
daddr, &p_id->identifier);
err = parse_tcp_identifier(ctx, is_egress, saddr, daddr,
&p_id->identifier);
if (err)
return -1;
} else {