view src/event/quic/bpf/ngx_quic_reuseport_helper.c @ 9153:8f7e6d8c061e

QUIC: use last client dcid to receive initial packets. Previously, original dcid was used to receive initial client packets in case server initial response was lost. However, last dcid should be used instead. These two are the same unless retry is used. In case of retry, client resends initial packet with a new dcid, that is different from the original dcid. If server response is lost, the client resends this packet again with the same dcid. This is shown in RFC 9000, 7.3. Authenticating Connection IDs, Figure 8. The issue manifested itself with creating multiple server sessions in response to each post-retry client initial packet, if server response is lost.
author Roman Arutyunyan <arut@nginx.com>
date Wed, 30 Aug 2023 11:09:21 +0400
parents a2fbae359828
children
line wrap: on
line source

#include <errno.h>
#include <linux/string.h>
#include <linux/udp.h>
#include <linux/bpf.h>
/*
 * the bpf_helpers.h is not included into linux-headers, only available
 * with kernel sources in "tools/lib/bpf/bpf_helpers.h" or in libbpf.
 */
#include <bpf/bpf_helpers.h>


#if !defined(SEC)
#define SEC(NAME)  __attribute__((section(NAME), used))
#endif


#if defined(LICENSE_GPL)

/*
 * To see debug:
 *
 *  echo 1 > /sys/kernel/debug/tracing/events/bpf_trace/enable
 *  cat /sys/kernel/debug/tracing/trace_pipe
 *  echo 0 > /sys/kernel/debug/tracing/events/bpf_trace/enable
 */

#define debugmsg(fmt, ...)                                                    \
do {                                                                          \
    char __buf[] = fmt;                                                       \
    bpf_trace_printk(__buf, sizeof(__buf), ##__VA_ARGS__);                    \
} while (0)

#else

#define debugmsg(fmt, ...)

#endif

char _license[] SEC("license") = LICENSE;

/*****************************************************************************/

#define NGX_QUIC_PKT_LONG        0x80  /* header form */
#define NGX_QUIC_SERVER_CID_LEN  20


#define advance_data(nbytes)                                                  \
    offset += nbytes;                                                         \
    if (start + offset > end) {                                               \
        debugmsg("cannot read %ld bytes at offset %ld", nbytes, offset);      \
        goto failed;                                                          \
    }                                                                         \
    data = start + offset - 1;


#define ngx_quic_parse_uint64(p)                                              \
    (((__u64)(p)[0] << 56) |                                                  \
     ((__u64)(p)[1] << 48) |                                                  \
     ((__u64)(p)[2] << 40) |                                                  \
     ((__u64)(p)[3] << 32) |                                                  \
     ((__u64)(p)[4] << 24) |                                                  \
     ((__u64)(p)[5] << 16) |                                                  \
     ((__u64)(p)[6] << 8)  |                                                  \
     ((__u64)(p)[7]))

/*
 * actual map object is created by the "bpf" system call,
 * all pointers to this variable are replaced by the bpf loader
 */
struct bpf_map_def SEC("maps") ngx_quic_sockmap;


SEC(PROGNAME)
int ngx_quic_select_socket_by_dcid(struct sk_reuseport_md *ctx)
{
    int             rc;
    __u64           key;
    size_t          len, offset;
    unsigned char  *start, *end, *data, *dcid;

    start = ctx->data;
    end = (unsigned char *) ctx->data_end;
    offset = 0;

    advance_data(sizeof(struct udphdr)); /* data at UDP header */
    advance_data(1); /* data at QUIC flags */

    if (data[0] & NGX_QUIC_PKT_LONG) {

        advance_data(4); /* data at QUIC version */
        advance_data(1); /* data at DCID len */

        len = data[0];   /* read DCID length */

        if (len < 8) {
            /* it's useless to search for key in such short DCID */
            return SK_PASS;
        }

    } else {
        len = NGX_QUIC_SERVER_CID_LEN;
    }

    dcid = &data[1];
    advance_data(len); /* we expect the packet to have full DCID */

    /* make verifier happy */
    if (dcid + sizeof(__u64) > end) {
        goto failed;
    }

    key = ngx_quic_parse_uint64(dcid);

    rc = bpf_sk_select_reuseport(ctx, &ngx_quic_sockmap, &key, 0);

    switch (rc) {
    case 0:
        debugmsg("nginx quic socket selected by key 0x%llx", key);
        return SK_PASS;

    /* kernel returns positive error numbers, errno.h defines positive */
    case -ENOENT:
        debugmsg("nginx quic default route for key 0x%llx", key);
        /* let the default reuseport logic decide which socket to choose */
        return SK_PASS;

    default:
        debugmsg("nginx quic bpf_sk_select_reuseport err: %d key 0x%llx",
                 rc, key);
        goto failed;
    }

failed:
    /*
     * SK_DROP will generate ICMP, but we may want to process "invalid" packet
     * in userspace quic to investigate further and finally react properly
     * (maybe ignore, maybe send something in response or close connection)
     */
    return SK_PASS;
}