esp4.c

Go to the documentation of this file.

#define pr_fmt(fmt) "IPsec: " fmt

#include <crypto/aead.h>
#include <crypto/authenc.h>
#include <linux/err.h>
#include <linux/module.h>
#include <net/ip.h>
#include <net/xfrm.h>
#include <net/esp.h>
#include <linux/scatterlist.h>
#include <linux/kernel.h>
#include <linux/pfkeyv2.h>
#include <linux/rtnetlink.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/in6.h>
#include <net/icmp.h>
#include <net/protocol.h>
#include <net/udp.h>

struct esp_skb_cb {
    struct xfrm_skb_cb xfrm;
    void *tmp;
};

#define ESP_SKB_CB(__skb) ((struct esp_skb_cb *)&((__skb)->cb[0]))

static u32 esp4_get_mtu(struct xfrm_state *x, int mtu);

/*
 * Allocate an AEAD request structure with extra space for SG and IV.
 *
 * For alignment considerations the IV is placed at the front, followed
 * by the request and finally the SG list.
 *
 * TODO: Use spare space in skb for this where possible.
 */
static void *esp_alloc_tmp(struct crypto_aead *aead, int nfrags, int seqhilen)
{
    unsigned int len;

    len = seqhilen;

    len += crypto_aead_ivsize(aead);

    if (len) {
        len += crypto_aead_alignmask(aead) &
               ~(crypto_tfm_ctx_alignment() - 1);
        len = ALIGN(len, crypto_tfm_ctx_alignment());
    }

    len += sizeof(struct aead_givcrypt_request) + crypto_aead_reqsize(aead);
    len = ALIGN(len, __alignof__(struct scatterlist));

    len += sizeof(struct scatterlist) * nfrags;

    return kmalloc(len, GFP_ATOMIC);
}

static inline __be32 *esp_tmp_seqhi(void *tmp)
{
    return PTR_ALIGN((__be32 *)tmp, __alignof__(__be32));
}
static inline u8 *esp_tmp_iv(struct crypto_aead *aead, void *tmp, int seqhilen)
{
    return crypto_aead_ivsize(aead) ?
           PTR_ALIGN((u8 *)tmp + seqhilen,
             crypto_aead_alignmask(aead) + 1) : tmp + seqhilen;
}

static inline struct aead_givcrypt_request *esp_tmp_givreq(
    struct crypto_aead *aead, u8 *iv)
{
    struct aead_givcrypt_request *req;

    req = (void *)PTR_ALIGN(iv + crypto_aead_ivsize(aead),
                crypto_tfm_ctx_alignment());
    aead_givcrypt_set_tfm(req, aead);
    return req;
}

static inline struct aead_request *esp_tmp_req(struct crypto_aead *aead, u8 *iv)
{
    struct aead_request *req;

    req = (void *)PTR_ALIGN(iv + crypto_aead_ivsize(aead),
                crypto_tfm_ctx_alignment());
    aead_request_set_tfm(req, aead);
    return req;
}

static inline struct scatterlist *esp_req_sg(struct crypto_aead *aead,
                         struct aead_request *req)
{
    return (void *)ALIGN((unsigned long)(req + 1) +
                 crypto_aead_reqsize(aead),
                 __alignof__(struct scatterlist));
}

static inline struct scatterlist *esp_givreq_sg(
    struct crypto_aead *aead, struct aead_givcrypt_request *req)
{
    return (void *)ALIGN((unsigned long)(req + 1) +
                 crypto_aead_reqsize(aead),
                 __alignof__(struct scatterlist));
}

static void esp_output_done(struct crypto_async_request *base, int err)
{
    struct sk_buff *skb = base->data;

    kfree(ESP_SKB_CB(skb)->tmp);
    xfrm_output_resume(skb, err);
}

static int esp_output(struct xfrm_state *x, struct sk_buff *skb)
{
    int err;
    struct ip_esp_hdr *esph;
    struct crypto_aead *aead;
    struct aead_givcrypt_request *req;
    struct scatterlist *sg;
    struct scatterlist *asg;
    struct esp_data *esp;
    struct sk_buff *trailer;
    void *tmp;
    u8 *iv;
    u8 *tail;
    int blksize;
    int clen;
    int alen;
    int plen;
    int tfclen;
    int nfrags;
    int assoclen;
    int sglists;
    int seqhilen;
    __be32 *seqhi;

    /* skb is pure payload to encrypt */

    err = -ENOMEM;

    esp = x->data;
    aead = esp->aead;
    alen = crypto_aead_authsize(aead);

    tfclen = 0;
    if (x->tfcpad) {
        struct xfrm_dst *dst = (struct xfrm_dst *)skb_dst(skb);
        u32 padto;

        padto = min(x->tfcpad, esp4_get_mtu(x, dst->child_mtu_cached));
        if (skb->len < padto)
            tfclen = padto - skb->len;
    }
    blksize = ALIGN(crypto_aead_blocksize(aead), 4);
    clen = ALIGN(skb->len + 2 + tfclen, blksize);
    if (esp->padlen)
        clen = ALIGN(clen, esp->padlen);
    plen = clen - skb->len - tfclen;

    err = skb_cow_data(skb, tfclen + plen + alen, &trailer);
    if (err < 0)
        goto error;
    nfrags = err;

    assoclen = sizeof(*esph);
    sglists = 1;
    seqhilen = 0;

    if (x->props.flags & XFRM_STATE_ESN) {
        sglists += 2;
        seqhilen += sizeof(__be32);
        assoclen += seqhilen;
    }

    tmp = esp_alloc_tmp(aead, nfrags + sglists, seqhilen);
    if (!tmp)
        goto error;

    seqhi = esp_tmp_seqhi(tmp);
    iv = esp_tmp_iv(aead, tmp, seqhilen);
    req = esp_tmp_givreq(aead, iv);
    asg = esp_givreq_sg(aead, req);
    sg = asg + sglists;

    /* Fill padding... */
    tail = skb_tail_pointer(trailer);
    if (tfclen) {
        memset(tail, 0, tfclen);
        tail += tfclen;
    }
    do {
        int i;
        for (i = 0; i < plen - 2; i++)
            tail[i] = i + 1;
    } while (0);
    tail[plen - 2] = plen - 2;
    tail[plen - 1] = *skb_mac_header(skb);
    pskb_put(skb, trailer, clen - skb->len + alen);

    skb_push(skb, -skb_network_offset(skb));
    esph = ip_esp_hdr(skb);
    *skb_mac_header(skb) = IPPROTO_ESP;

    /* this is non-NULL only with UDP Encapsulation */
    if (x->encap) {
        struct xfrm_encap_tmpl *encap = x->encap;
        struct udphdr *uh;
        __be32 *udpdata32;
        __be16 sport, dport;
        int encap_type;

        spin_lock_bh(&x->lock);
        sport = encap->encap_sport;
        dport = encap->encap_dport;
        encap_type = encap->encap_type;
        spin_unlock_bh(&x->lock);

        uh = (struct udphdr *)esph;
        uh->source = sport;
        uh->dest = dport;
        uh->len = htons(skb->len - skb_transport_offset(skb));
        uh->check = 0;

        switch (encap_type) {
        default:
        case UDP_ENCAP_ESPINUDP:
            esph = (struct ip_esp_hdr *)(uh + 1);
            break;
        case UDP_ENCAP_ESPINUDP_NON_IKE:
            udpdata32 = (__be32 *)(uh + 1);
            udpdata32[0] = udpdata32[1] = 0;
            esph = (struct ip_esp_hdr *)(udpdata32 + 2);
            break;
        }

        *skb_mac_header(skb) = IPPROTO_UDP;
    }

    esph->spi = x->id.spi;
    esph->seq_no = htonl(XFRM_SKB_CB(skb)->seq.output.low);

    sg_init_table(sg, nfrags);
    skb_to_sgvec(skb, sg,
             esph->enc_data + crypto_aead_ivsize(aead) - skb->data,
             clen + alen);

    if ((x->props.flags & XFRM_STATE_ESN)) {
        sg_init_table(asg, 3);
        sg_set_buf(asg, &esph->spi, sizeof(__be32));
        *seqhi = htonl(XFRM_SKB_CB(skb)->seq.output.hi);
        sg_set_buf(asg + 1, seqhi, seqhilen);
        sg_set_buf(asg + 2, &esph->seq_no, sizeof(__be32));
    } else
        sg_init_one(asg, esph, sizeof(*esph));

    aead_givcrypt_set_callback(req, 0, esp_output_done, skb);
    aead_givcrypt_set_crypt(req, sg, sg, clen, iv);
    aead_givcrypt_set_assoc(req, asg, assoclen);
    aead_givcrypt_set_giv(req, esph->enc_data,
                  XFRM_SKB_CB(skb)->seq.output.low);

    ESP_SKB_CB(skb)->tmp = tmp;
    err = crypto_aead_givencrypt(req);
    if (err == -EINPROGRESS)
        goto error;

    if (err == -EBUSY)
        err = NET_XMIT_DROP;

    kfree(tmp);

error:
    return err;
}

static int esp_input_done2(struct sk_buff *skb, int err)
{
    const struct iphdr *iph;
    struct xfrm_state *x = xfrm_input_state(skb);
    struct esp_data *esp = x->data;
    struct crypto_aead *aead = esp->aead;
    int alen = crypto_aead_authsize(aead);
    int hlen = sizeof(struct ip_esp_hdr) + crypto_aead_ivsize(aead);
    int elen = skb->len - hlen;
    int ihl;
    u8 nexthdr[2];
    int padlen;

    kfree(ESP_SKB_CB(skb)->tmp);

    if (unlikely(err))
        goto out;

    if (skb_copy_bits(skb, skb->len-alen-2, nexthdr, 2))
        BUG();

    err = -EINVAL;
    padlen = nexthdr[0];
    if (padlen + 2 + alen >= elen)
        goto out;

    /* ... check padding bits here. Silly. :-) */

    iph = ip_hdr(skb);
    ihl = iph->ihl * 4;

    if (x->encap) {
        struct xfrm_encap_tmpl *encap = x->encap;
        struct udphdr *uh = (void *)(skb_network_header(skb) + ihl);

        /*
         * 1) if the NAT-T peer's IP or port changed then
         *    advertize the change to the keying daemon.
         *    This is an inbound SA, so just compare
         *    SRC ports.
         */
        if (iph->saddr != x->props.saddr.a4 ||
            uh->source != encap->encap_sport) {
            xfrm_address_t ipaddr;

            ipaddr.a4 = iph->saddr;
            km_new_mapping(x, &ipaddr, uh->source);

            /* XXX: perhaps add an extra
             * policy check here, to see
             * if we should allow or
             * reject a packet from a
             * different source
             * address/port.
             */
        }

        /*
         * 2) ignore UDP/TCP checksums in case
         *    of NAT-T in Transport Mode, or
         *    perform other post-processing fixes
         *    as per draft-ietf-ipsec-udp-encaps-06,
         *    section 3.1.2
         */
        if (x->props.mode == XFRM_MODE_TRANSPORT)
            skb->ip_summed = CHECKSUM_UNNECESSARY;
    }

    pskb_trim(skb, skb->len - alen - padlen - 2);
    __skb_pull(skb, hlen);
    skb_set_transport_header(skb, -ihl);

    err = nexthdr[1];

    /* RFC4303: Drop dummy packets without any error */
    if (err == IPPROTO_NONE)
        err = -EINVAL;

out:
    return err;
}

static void esp_input_done(struct crypto_async_request *base, int err)
{
    struct sk_buff *skb = base->data;

    xfrm_input_resume(skb, esp_input_done2(skb, err));
}

/*
 * Note: detecting truncated vs. non-truncated authentication data is very
 * expensive, so we only support truncated data, which is the recommended
 * and common case.
 */
static int esp_input(struct xfrm_state *x, struct sk_buff *skb)
{
    struct ip_esp_hdr *esph;
    struct esp_data *esp = x->data;
    struct crypto_aead *aead = esp->aead;
    struct aead_request *req;
    struct sk_buff *trailer;
    int elen = skb->len - sizeof(*esph) - crypto_aead_ivsize(aead);
    int nfrags;
    int assoclen;
    int sglists;
    int seqhilen;
    __be32 *seqhi;
    void *tmp;
    u8 *iv;
    struct scatterlist *sg;
    struct scatterlist *asg;
    int err = -EINVAL;

    if (!pskb_may_pull(skb, sizeof(*esph) + crypto_aead_ivsize(aead)))
        goto out;

    if (elen <= 0)
        goto out;

    if ((err = skb_cow_data(skb, 0, &trailer)) < 0)
        goto out;
    nfrags = err;

    assoclen = sizeof(*esph);
    sglists = 1;
    seqhilen = 0;

    if (x->props.flags & XFRM_STATE_ESN) {
        sglists += 2;
        seqhilen += sizeof(__be32);
        assoclen += seqhilen;
    }

    err = -ENOMEM;
    tmp = esp_alloc_tmp(aead, nfrags + sglists, seqhilen);
    if (!tmp)
        goto out;

    ESP_SKB_CB(skb)->tmp = tmp;
    seqhi = esp_tmp_seqhi(tmp);
    iv = esp_tmp_iv(aead, tmp, seqhilen);
    req = esp_tmp_req(aead, iv);
    asg = esp_req_sg(aead, req);
    sg = asg + sglists;

    skb->ip_summed = CHECKSUM_NONE;

    esph = (struct ip_esp_hdr *)skb->data;

    /* Get ivec. This can be wrong, check against another impls. */
    iv = esph->enc_data;

    sg_init_table(sg, nfrags);
    skb_to_sgvec(skb, sg, sizeof(*esph) + crypto_aead_ivsize(aead), elen);

    if ((x->props.flags & XFRM_STATE_ESN)) {
        sg_init_table(asg, 3);
        sg_set_buf(asg, &esph->spi, sizeof(__be32));
        *seqhi = XFRM_SKB_CB(skb)->seq.input.hi;
        sg_set_buf(asg + 1, seqhi, seqhilen);
        sg_set_buf(asg + 2, &esph->seq_no, sizeof(__be32));
    } else
        sg_init_one(asg, esph, sizeof(*esph));

    aead_request_set_callback(req, 0, esp_input_done, skb);
    aead_request_set_crypt(req, sg, sg, elen, iv);
    aead_request_set_assoc(req, asg, assoclen);

    err = crypto_aead_decrypt(req);
    if (err == -EINPROGRESS)
        goto out;

    err = esp_input_done2(skb, err);

out:
    return err;
}

static u32 esp4_get_mtu(struct xfrm_state *x, int mtu)
{
    struct esp_data *esp = x->data;
    u32 blksize = ALIGN(crypto_aead_blocksize(esp->aead), 4);
    u32 align = max_t(u32, blksize, esp->padlen);
    unsigned int net_adj;

    switch (x->props.mode) {
    case XFRM_MODE_TRANSPORT:
    case XFRM_MODE_BEET:
        net_adj = sizeof(struct iphdr);
        break;
    case XFRM_MODE_TUNNEL:
        net_adj = 0;
        break;
    default:
        BUG();
    }

    return ((mtu - x->props.header_len - crypto_aead_authsize(esp->aead) -
         net_adj) & ~(align - 1)) + (net_adj - 2);
}

static void esp4_err(struct sk_buff *skb, u32 info)
{
    struct net *net = dev_net(skb->dev);
    const struct iphdr *iph = (const struct iphdr *)skb->data;
    struct ip_esp_hdr *esph = (struct ip_esp_hdr *)(skb->data+(iph->ihl<<2));
    struct xfrm_state *x;

    switch (icmp_hdr(skb)->type) {
    case ICMP_DEST_UNREACH:
        if (icmp_hdr(skb)->code != ICMP_FRAG_NEEDED)
            return;
    case ICMP_REDIRECT:
        break;
    default:
        return;
    }

    x = xfrm_state_lookup(net, skb->mark, (const xfrm_address_t *)&iph->daddr,
                  esph->spi, IPPROTO_ESP, AF_INET);
    if (!x)
        return;

    if (icmp_hdr(skb)->type == ICMP_DEST_UNREACH)
        ipv4_update_pmtu(skb, net, info, 0, 0, IPPROTO_ESP, 0);
    else
        ipv4_redirect(skb, net, 0, 0, IPPROTO_ESP, 0);
    xfrm_state_put(x);
}

static void esp_destroy(struct xfrm_state *x)
{
    struct esp_data *esp = x->data;

    if (!esp)
        return;

    crypto_free_aead(esp->aead);
    kfree(esp);
}

static int esp_init_aead(struct xfrm_state *x)
{
    struct esp_data *esp = x->data;
    struct crypto_aead *aead;
    int err;

    aead = crypto_alloc_aead(x->aead->alg_name, 0, 0);
    err = PTR_ERR(aead);
    if (IS_ERR(aead))
        goto error;

    esp->aead = aead;

    err = crypto_aead_setkey(aead, x->aead->alg_key,
                 (x->aead->alg_key_len + 7) / 8);
    if (err)
        goto error;

    err = crypto_aead_setauthsize(aead, x->aead->alg_icv_len / 8);
    if (err)
        goto error;

error:
    return err;
}

static int esp_init_authenc(struct xfrm_state *x)
{
    struct esp_data *esp = x->data;
    struct crypto_aead *aead;
    struct crypto_authenc_key_param *param;
    struct rtattr *rta;
    char *key;
    char *p;
    char authenc_name[CRYPTO_MAX_ALG_NAME];
    unsigned int keylen;
    int err;

    err = -EINVAL;
    if (x->ealg == NULL)
        goto error;

    err = -ENAMETOOLONG;

    if ((x->props.flags & XFRM_STATE_ESN)) {
        if (snprintf(authenc_name, CRYPTO_MAX_ALG_NAME,
                 "authencesn(%s,%s)",
                 x->aalg ? x->aalg->alg_name : "digest_null",
                 x->ealg->alg_name) >= CRYPTO_MAX_ALG_NAME)
            goto error;
    } else {
        if (snprintf(authenc_name, CRYPTO_MAX_ALG_NAME,
                 "authenc(%s,%s)",
                 x->aalg ? x->aalg->alg_name : "digest_null",
                 x->ealg->alg_name) >= CRYPTO_MAX_ALG_NAME)
            goto error;
    }

    aead = crypto_alloc_aead(authenc_name, 0, 0);
    err = PTR_ERR(aead);
    if (IS_ERR(aead))
        goto error;

    esp->aead = aead;

    keylen = (x->aalg ? (x->aalg->alg_key_len + 7) / 8 : 0) +
         (x->ealg->alg_key_len + 7) / 8 + RTA_SPACE(sizeof(*param));
    err = -ENOMEM;
    key = kmalloc(keylen, GFP_KERNEL);
    if (!key)
        goto error;

    p = key;
    rta = (void *)p;
    rta->rta_type = CRYPTO_AUTHENC_KEYA_PARAM;
    rta->rta_len = RTA_LENGTH(sizeof(*param));
    param = RTA_DATA(rta);
    p += RTA_SPACE(sizeof(*param));

    if (x->aalg) {
        struct xfrm_algo_desc *aalg_desc;

        memcpy(p, x->aalg->alg_key, (x->aalg->alg_key_len + 7) / 8);
        p += (x->aalg->alg_key_len + 7) / 8;

        aalg_desc = xfrm_aalg_get_byname(x->aalg->alg_name, 0);
        BUG_ON(!aalg_desc);

        err = -EINVAL;
        if (aalg_desc->uinfo.auth.icv_fullbits/8 !=
            crypto_aead_authsize(aead)) {
            NETDEBUG(KERN_INFO "ESP: %s digestsize %u != %hu\n",
                 x->aalg->alg_name,
                 crypto_aead_authsize(aead),
                 aalg_desc->uinfo.auth.icv_fullbits/8);
            goto free_key;
        }

        err = crypto_aead_setauthsize(
            aead, x->aalg->alg_trunc_len / 8);
        if (err)
            goto free_key;
    }

    param->enckeylen = cpu_to_be32((x->ealg->alg_key_len + 7) / 8);
    memcpy(p, x->ealg->alg_key, (x->ealg->alg_key_len + 7) / 8);

    err = crypto_aead_setkey(aead, key, keylen);

free_key:
    kfree(key);

error:
    return err;
}

static int esp_init_state(struct xfrm_state *x)
{
    struct esp_data *esp;
    struct crypto_aead *aead;
    u32 align;
    int err;

    esp = kzalloc(sizeof(*esp), GFP_KERNEL);
    if (esp == NULL)
        return -ENOMEM;

    x->data = esp;

    if (x->aead)
        err = esp_init_aead(x);
    else
        err = esp_init_authenc(x);

    if (err)
        goto error;

    aead = esp->aead;

    esp->padlen = 0;

    x->props.header_len = sizeof(struct ip_esp_hdr) +
                  crypto_aead_ivsize(aead);
    if (x->props.mode == XFRM_MODE_TUNNEL)
        x->props.header_len += sizeof(struct iphdr);
    else if (x->props.mode == XFRM_MODE_BEET && x->sel.family != AF_INET6)
        x->props.header_len += IPV4_BEET_PHMAXLEN;
    if (x->encap) {
        struct xfrm_encap_tmpl *encap = x->encap;

        switch (encap->encap_type) {
        default:
            goto error;
        case UDP_ENCAP_ESPINUDP:
            x->props.header_len += sizeof(struct udphdr);
            break;
        case UDP_ENCAP_ESPINUDP_NON_IKE:
            x->props.header_len += sizeof(struct udphdr) + 2 * sizeof(u32);
            break;
        }
    }

    align = ALIGN(crypto_aead_blocksize(aead), 4);
    if (esp->padlen)
        align = max_t(u32, align, esp->padlen);
    x->props.trailer_len = align + 1 + crypto_aead_authsize(esp->aead);

error:
    return err;
}

static const struct xfrm_type esp_type =
{
    .description    = "ESP4",
    .owner      = THIS_MODULE,
    .proto          = IPPROTO_ESP,
    .flags      = XFRM_TYPE_REPLAY_PROT,
    .init_state = esp_init_state,
    .destructor = esp_destroy,
    .get_mtu    = esp4_get_mtu,
    .input      = esp_input,
    .output     = esp_output
};

static const struct net_protocol esp4_protocol = {
    .handler    =   xfrm4_rcv,
    .err_handler    =   esp4_err,
    .no_policy  =   1,
    .netns_ok   =   1,
};

static int __init esp4_init(void)
{
    if (xfrm_register_type(&esp_type, AF_INET) < 0) {
        pr_info("%s: can't add xfrm type\n", __func__);
        return -EAGAIN;
    }
    if (inet_add_protocol(&esp4_protocol, IPPROTO_ESP) < 0) {
        pr_info("%s: can't add protocol\n", __func__);
        xfrm_unregister_type(&esp_type, AF_INET);
        return -EAGAIN;
    }
    return 0;
}

static void __exit esp4_fini(void)
{
    if (inet_del_protocol(&esp4_protocol, IPPROTO_ESP) < 0)
        pr_info("%s: can't remove protocol\n", __func__);
    if (xfrm_unregister_type(&esp_type, AF_INET) < 0)
        pr_info("%s: can't remove xfrm type\n", __func__);
}

module_init(esp4_init);
module_exit(esp4_fini);
MODULE_LICENSE("GPL");
MODULE_ALIAS_XFRM_TYPE(AF_INET, XFRM_PROTO_ESP);