secure_seq.c

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#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/cryptohash.h>
#include <linux/module.h>
#include <linux/cache.h>
#include <linux/random.h>
#include <linux/hrtimer.h>
#include <linux/ktime.h>
#include <linux/string.h>

#include <net/secure_seq.h>

static u32 net_secret[MD5_MESSAGE_BYTES / 4] ____cacheline_aligned;

static int __init net_secret_init(void)
{
    get_random_bytes(net_secret, sizeof(net_secret));
    return 0;
}
late_initcall(net_secret_init);

#ifdef CONFIG_INET
static u32 seq_scale(u32 seq)
{
    /*
     *  As close as possible to RFC 793, which
     *  suggests using a 250 kHz clock.
     *  Further reading shows this assumes 2 Mb/s networks.
     *  For 10 Mb/s Ethernet, a 1 MHz clock is appropriate.
     *  For 10 Gb/s Ethernet, a 1 GHz clock should be ok, but
     *  we also need to limit the resolution so that the u32 seq
     *  overlaps less than one time per MSL (2 minutes).
     *  Choosing a clock of 64 ns period is OK. (period of 274 s)
     */
    return seq + (ktime_to_ns(ktime_get_real()) >> 6);
}
#endif

#if IS_ENABLED(CONFIG_IPV6)
__u32 secure_tcpv6_sequence_number(const __be32 *saddr, const __be32 *daddr,
                   __be16 sport, __be16 dport)
{
    u32 secret[MD5_MESSAGE_BYTES / 4];
    u32 hash[MD5_DIGEST_WORDS];
    u32 i;

    memcpy(hash, saddr, 16);
    for (i = 0; i < 4; i++)
        secret[i] = net_secret[i] + (__force u32)daddr[i];
    secret[4] = net_secret[4] +
        (((__force u16)sport << 16) + (__force u16)dport);
    for (i = 5; i < MD5_MESSAGE_BYTES / 4; i++)
        secret[i] = net_secret[i];

    md5_transform(hash, secret);

    return seq_scale(hash[0]);
}
EXPORT_SYMBOL(secure_tcpv6_sequence_number);

u32 secure_ipv6_port_ephemeral(const __be32 *saddr, const __be32 *daddr,
                   __be16 dport)
{
    u32 secret[MD5_MESSAGE_BYTES / 4];
    u32 hash[MD5_DIGEST_WORDS];
    u32 i;

    memcpy(hash, saddr, 16);
    for (i = 0; i < 4; i++)
        secret[i] = net_secret[i] + (__force u32) daddr[i];
    secret[4] = net_secret[4] + (__force u32)dport;
    for (i = 5; i < MD5_MESSAGE_BYTES / 4; i++)
        secret[i] = net_secret[i];

    md5_transform(hash, secret);

    return hash[0];
}
EXPORT_SYMBOL(secure_ipv6_port_ephemeral);
#endif

#ifdef CONFIG_INET
__u32 secure_ip_id(__be32 daddr)
{
    u32 hash[MD5_DIGEST_WORDS];

    hash[0] = (__force __u32) daddr;
    hash[1] = net_secret[13];
    hash[2] = net_secret[14];
    hash[3] = net_secret[15];

    md5_transform(hash, net_secret);

    return hash[0];
}

__u32 secure_ipv6_id(const __be32 daddr[4])
{
    __u32 hash[4];

    memcpy(hash, daddr, 16);
    md5_transform(hash, net_secret);

    return hash[0];
}

__u32 secure_tcp_sequence_number(__be32 saddr, __be32 daddr,
                 __be16 sport, __be16 dport)
{
    u32 hash[MD5_DIGEST_WORDS];

    hash[0] = (__force u32)saddr;
    hash[1] = (__force u32)daddr;
    hash[2] = ((__force u16)sport << 16) + (__force u16)dport;
    hash[3] = net_secret[15];

    md5_transform(hash, net_secret);

    return seq_scale(hash[0]);
}

u32 secure_ipv4_port_ephemeral(__be32 saddr, __be32 daddr, __be16 dport)
{
    u32 hash[MD5_DIGEST_WORDS];

    hash[0] = (__force u32)saddr;
    hash[1] = (__force u32)daddr;
    hash[2] = (__force u32)dport ^ net_secret[14];
    hash[3] = net_secret[15];

    md5_transform(hash, net_secret);

    return hash[0];
}
EXPORT_SYMBOL_GPL(secure_ipv4_port_ephemeral);
#endif

#if IS_ENABLED(CONFIG_IP_DCCP)
u64 secure_dccp_sequence_number(__be32 saddr, __be32 daddr,
                __be16 sport, __be16 dport)
{
    u32 hash[MD5_DIGEST_WORDS];
    u64 seq;

    hash[0] = (__force u32)saddr;
    hash[1] = (__force u32)daddr;
    hash[2] = ((__force u16)sport << 16) + (__force u16)dport;
    hash[3] = net_secret[15];

    md5_transform(hash, net_secret);

    seq = hash[0] | (((u64)hash[1]) << 32);
    seq += ktime_to_ns(ktime_get_real());
    seq &= (1ull << 48) - 1;

    return seq;
}
EXPORT_SYMBOL(secure_dccp_sequence_number);

#if IS_ENABLED(CONFIG_IPV6)
u64 secure_dccpv6_sequence_number(__be32 *saddr, __be32 *daddr,
                  __be16 sport, __be16 dport)
{
    u32 secret[MD5_MESSAGE_BYTES / 4];
    u32 hash[MD5_DIGEST_WORDS];
    u64 seq;
    u32 i;

    memcpy(hash, saddr, 16);
    for (i = 0; i < 4; i++)
        secret[i] = net_secret[i] + daddr[i];
    secret[4] = net_secret[4] +
        (((__force u16)sport << 16) + (__force u16)dport);
    for (i = 5; i < MD5_MESSAGE_BYTES / 4; i++)
        secret[i] = net_secret[i];

    md5_transform(hash, secret);

    seq = hash[0] | (((u64)hash[1]) << 32);
    seq += ktime_to_ns(ktime_get_real());
    seq &= (1ull << 48) - 1;

    return seq;
}
EXPORT_SYMBOL(secure_dccpv6_sequence_number);
#endif
#endif