ah4.c

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#define pr_fmt(fmt) "IPsec: " fmt

#include <crypto/hash.h>
#include <linux/err.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <net/ip.h>
#include <net/xfrm.h>
#include <net/ah.h>
#include <linux/crypto.h>
#include <linux/pfkeyv2.h>
#include <linux/scatterlist.h>
#include <net/icmp.h>
#include <net/protocol.h>

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

#define AH_SKB_CB(__skb) ((struct ah_skb_cb *)&((__skb)->cb[0]))

static void *ah_alloc_tmp(struct crypto_ahash *ahash, int nfrags,
              unsigned int size)
{
    unsigned int len;

    len = size + crypto_ahash_digestsize(ahash) +
          (crypto_ahash_alignmask(ahash) &
           ~(crypto_tfm_ctx_alignment() - 1));

    len = ALIGN(len, crypto_tfm_ctx_alignment());

    len += sizeof(struct ahash_request) + crypto_ahash_reqsize(ahash);
    len = ALIGN(len, __alignof__(struct scatterlist));

    len += sizeof(struct scatterlist) * nfrags;

    return kmalloc(len, GFP_ATOMIC);
}

static inline u8 *ah_tmp_auth(void *tmp, unsigned int offset)
{
    return tmp + offset;
}

static inline u8 *ah_tmp_icv(struct crypto_ahash *ahash, void *tmp,
                 unsigned int offset)
{
    return PTR_ALIGN((u8 *)tmp + offset, crypto_ahash_alignmask(ahash) + 1);
}

static inline struct ahash_request *ah_tmp_req(struct crypto_ahash *ahash,
                           u8 *icv)
{
    struct ahash_request *req;

    req = (void *)PTR_ALIGN(icv + crypto_ahash_digestsize(ahash),
                crypto_tfm_ctx_alignment());

    ahash_request_set_tfm(req, ahash);

    return req;
}

static inline struct scatterlist *ah_req_sg(struct crypto_ahash *ahash,
                         struct ahash_request *req)
{
    return (void *)ALIGN((unsigned long)(req + 1) +
                 crypto_ahash_reqsize(ahash),
                 __alignof__(struct scatterlist));
}

/* Clear mutable options and find final destination to substitute
 * into IP header for icv calculation. Options are already checked
 * for validity, so paranoia is not required. */

static int ip_clear_mutable_options(const struct iphdr *iph, __be32 *daddr)
{
    unsigned char *optptr = (unsigned char *)(iph+1);
    int  l = iph->ihl*4 - sizeof(struct iphdr);
    int  optlen;

    while (l > 0) {
        switch (*optptr) {
        case IPOPT_END:
            return 0;
        case IPOPT_NOOP:
            l--;
            optptr++;
            continue;
        }
        optlen = optptr[1];
        if (optlen<2 || optlen>l)
            return -EINVAL;
        switch (*optptr) {
        case IPOPT_SEC:
        case 0x85:  /* Some "Extended Security" crap. */
        case IPOPT_CIPSO:
        case IPOPT_RA:
        case 0x80|21:   /* RFC1770 */
            break;
        case IPOPT_LSRR:
        case IPOPT_SSRR:
            if (optlen < 6)
                return -EINVAL;
            memcpy(daddr, optptr+optlen-4, 4);
            /* Fall through */
        default:
            memset(optptr, 0, optlen);
        }
        l -= optlen;
        optptr += optlen;
    }
    return 0;
}

static void ah_output_done(struct crypto_async_request *base, int err)
{
    u8 *icv;
    struct iphdr *iph;
    struct sk_buff *skb = base->data;
    struct xfrm_state *x = skb_dst(skb)->xfrm;
    struct ah_data *ahp = x->data;
    struct iphdr *top_iph = ip_hdr(skb);
    struct ip_auth_hdr *ah = ip_auth_hdr(skb);
    int ihl = ip_hdrlen(skb);

    iph = AH_SKB_CB(skb)->tmp;
    icv = ah_tmp_icv(ahp->ahash, iph, ihl);
    memcpy(ah->auth_data, icv, ahp->icv_trunc_len);

    top_iph->tos = iph->tos;
    top_iph->ttl = iph->ttl;
    top_iph->frag_off = iph->frag_off;
    if (top_iph->ihl != 5) {
        top_iph->daddr = iph->daddr;
        memcpy(top_iph+1, iph+1, top_iph->ihl*4 - sizeof(struct iphdr));
    }

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

static int ah_output(struct xfrm_state *x, struct sk_buff *skb)
{
    int err;
    int nfrags;
    int ihl;
    u8 *icv;
    struct sk_buff *trailer;
    struct crypto_ahash *ahash;
    struct ahash_request *req;
    struct scatterlist *sg;
    struct iphdr *iph, *top_iph;
    struct ip_auth_hdr *ah;
    struct ah_data *ahp;

    ahp = x->data;
    ahash = ahp->ahash;

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

    skb_push(skb, -skb_network_offset(skb));
    ah = ip_auth_hdr(skb);
    ihl = ip_hdrlen(skb);

    err = -ENOMEM;
    iph = ah_alloc_tmp(ahash, nfrags, ihl);
    if (!iph)
        goto out;

    icv = ah_tmp_icv(ahash, iph, ihl);
    req = ah_tmp_req(ahash, icv);
    sg = ah_req_sg(ahash, req);

    memset(ah->auth_data, 0, ahp->icv_trunc_len);

    top_iph = ip_hdr(skb);

    iph->tos = top_iph->tos;
    iph->ttl = top_iph->ttl;
    iph->frag_off = top_iph->frag_off;

    if (top_iph->ihl != 5) {
        iph->daddr = top_iph->daddr;
        memcpy(iph+1, top_iph+1, top_iph->ihl*4 - sizeof(struct iphdr));
        err = ip_clear_mutable_options(top_iph, &top_iph->daddr);
        if (err)
            goto out_free;
    }

    ah->nexthdr = *skb_mac_header(skb);
    *skb_mac_header(skb) = IPPROTO_AH;

    top_iph->tos = 0;
    top_iph->tot_len = htons(skb->len);
    top_iph->frag_off = 0;
    top_iph->ttl = 0;
    top_iph->check = 0;

    if (x->props.flags & XFRM_STATE_ALIGN4)
        ah->hdrlen  = (XFRM_ALIGN4(sizeof(*ah) + ahp->icv_trunc_len) >> 2) - 2;
    else
        ah->hdrlen  = (XFRM_ALIGN8(sizeof(*ah) + ahp->icv_trunc_len) >> 2) - 2;

    ah->reserved = 0;
    ah->spi = x->id.spi;
    ah->seq_no = htonl(XFRM_SKB_CB(skb)->seq.output.low);

    sg_init_table(sg, nfrags);
    skb_to_sgvec(skb, sg, 0, skb->len);

    ahash_request_set_crypt(req, sg, icv, skb->len);
    ahash_request_set_callback(req, 0, ah_output_done, skb);

    AH_SKB_CB(skb)->tmp = iph;

    err = crypto_ahash_digest(req);
    if (err) {
        if (err == -EINPROGRESS)
            goto out;

        if (err == -EBUSY)
            err = NET_XMIT_DROP;
        goto out_free;
    }

    memcpy(ah->auth_data, icv, ahp->icv_trunc_len);

    top_iph->tos = iph->tos;
    top_iph->ttl = iph->ttl;
    top_iph->frag_off = iph->frag_off;
    if (top_iph->ihl != 5) {
        top_iph->daddr = iph->daddr;
        memcpy(top_iph+1, iph+1, top_iph->ihl*4 - sizeof(struct iphdr));
    }

out_free:
    kfree(iph);
out:
    return err;
}

static void ah_input_done(struct crypto_async_request *base, int err)
{
    u8 *auth_data;
    u8 *icv;
    struct iphdr *work_iph;
    struct sk_buff *skb = base->data;
    struct xfrm_state *x = xfrm_input_state(skb);
    struct ah_data *ahp = x->data;
    struct ip_auth_hdr *ah = ip_auth_hdr(skb);
    int ihl = ip_hdrlen(skb);
    int ah_hlen = (ah->hdrlen + 2) << 2;

    work_iph = AH_SKB_CB(skb)->tmp;
    auth_data = ah_tmp_auth(work_iph, ihl);
    icv = ah_tmp_icv(ahp->ahash, auth_data, ahp->icv_trunc_len);

    err = memcmp(icv, auth_data, ahp->icv_trunc_len) ? -EBADMSG: 0;
    if (err)
        goto out;

    err = ah->nexthdr;

    skb->network_header += ah_hlen;
    memcpy(skb_network_header(skb), work_iph, ihl);
    __skb_pull(skb, ah_hlen + ihl);
    skb_set_transport_header(skb, -ihl);
out:
    kfree(AH_SKB_CB(skb)->tmp);
    xfrm_input_resume(skb, err);
}

static int ah_input(struct xfrm_state *x, struct sk_buff *skb)
{
    int ah_hlen;
    int ihl;
    int nexthdr;
    int nfrags;
    u8 *auth_data;
    u8 *icv;
    struct sk_buff *trailer;
    struct crypto_ahash *ahash;
    struct ahash_request *req;
    struct scatterlist *sg;
    struct iphdr *iph, *work_iph;
    struct ip_auth_hdr *ah;
    struct ah_data *ahp;
    int err = -ENOMEM;

    if (!pskb_may_pull(skb, sizeof(*ah)))
        goto out;

    ah = (struct ip_auth_hdr *)skb->data;
    ahp = x->data;
    ahash = ahp->ahash;

    nexthdr = ah->nexthdr;
    ah_hlen = (ah->hdrlen + 2) << 2;

    if (x->props.flags & XFRM_STATE_ALIGN4) {
        if (ah_hlen != XFRM_ALIGN4(sizeof(*ah) + ahp->icv_full_len) &&
            ah_hlen != XFRM_ALIGN4(sizeof(*ah) + ahp->icv_trunc_len))
            goto out;
    } else {
        if (ah_hlen != XFRM_ALIGN8(sizeof(*ah) + ahp->icv_full_len) &&
            ah_hlen != XFRM_ALIGN8(sizeof(*ah) + ahp->icv_trunc_len))
            goto out;
    }

    if (!pskb_may_pull(skb, ah_hlen))
        goto out;

    /* We are going to _remove_ AH header to keep sockets happy,
     * so... Later this can change. */
    if (skb_cloned(skb) &&
        pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
        goto out;

    skb->ip_summed = CHECKSUM_NONE;


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

    ah = (struct ip_auth_hdr *)skb->data;
    iph = ip_hdr(skb);
    ihl = ip_hdrlen(skb);

    work_iph = ah_alloc_tmp(ahash, nfrags, ihl + ahp->icv_trunc_len);
    if (!work_iph)
        goto out;

    auth_data = ah_tmp_auth(work_iph, ihl);
    icv = ah_tmp_icv(ahash, auth_data, ahp->icv_trunc_len);
    req = ah_tmp_req(ahash, icv);
    sg = ah_req_sg(ahash, req);

    memcpy(work_iph, iph, ihl);
    memcpy(auth_data, ah->auth_data, ahp->icv_trunc_len);
    memset(ah->auth_data, 0, ahp->icv_trunc_len);

    iph->ttl = 0;
    iph->tos = 0;
    iph->frag_off = 0;
    iph->check = 0;
    if (ihl > sizeof(*iph)) {
        __be32 dummy;
        err = ip_clear_mutable_options(iph, &dummy);
        if (err)
            goto out_free;
    }

    skb_push(skb, ihl);

    sg_init_table(sg, nfrags);
    skb_to_sgvec(skb, sg, 0, skb->len);

    ahash_request_set_crypt(req, sg, icv, skb->len);
    ahash_request_set_callback(req, 0, ah_input_done, skb);

    AH_SKB_CB(skb)->tmp = work_iph;

    err = crypto_ahash_digest(req);
    if (err) {
        if (err == -EINPROGRESS)
            goto out;

        goto out_free;
    }

    err = memcmp(icv, auth_data, ahp->icv_trunc_len) ? -EBADMSG: 0;
    if (err)
        goto out_free;

    skb->network_header += ah_hlen;
    memcpy(skb_network_header(skb), work_iph, ihl);
    __skb_pull(skb, ah_hlen + ihl);
    skb_set_transport_header(skb, -ihl);

    err = nexthdr;

out_free:
    kfree (work_iph);
out:
    return err;
}

static void ah4_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_auth_hdr *ah = (struct ip_auth_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,
                  ah->spi, IPPROTO_AH, AF_INET);
    if (!x)
        return;

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

static int ah_init_state(struct xfrm_state *x)
{
    struct ah_data *ahp = NULL;
    struct xfrm_algo_desc *aalg_desc;
    struct crypto_ahash *ahash;

    if (!x->aalg)
        goto error;

    if (x->encap)
        goto error;

    ahp = kzalloc(sizeof(*ahp), GFP_KERNEL);
    if (!ahp)
        return -ENOMEM;

    ahash = crypto_alloc_ahash(x->aalg->alg_name, 0, 0);
    if (IS_ERR(ahash))
        goto error;

    ahp->ahash = ahash;
    if (crypto_ahash_setkey(ahash, x->aalg->alg_key,
                (x->aalg->alg_key_len + 7) / 8))
        goto error;

    /*
     * Lookup the algorithm description maintained by xfrm_algo,
     * verify crypto transform properties, and store information
     * we need for AH processing.  This lookup cannot fail here
     * after a successful crypto_alloc_ahash().
     */
    aalg_desc = xfrm_aalg_get_byname(x->aalg->alg_name, 0);
    BUG_ON(!aalg_desc);

    if (aalg_desc->uinfo.auth.icv_fullbits/8 !=
        crypto_ahash_digestsize(ahash)) {
        pr_info("%s: %s digestsize %u != %hu\n",
            __func__, x->aalg->alg_name,
            crypto_ahash_digestsize(ahash),
            aalg_desc->uinfo.auth.icv_fullbits / 8);
        goto error;
    }

    ahp->icv_full_len = aalg_desc->uinfo.auth.icv_fullbits/8;
    ahp->icv_trunc_len = x->aalg->alg_trunc_len/8;

    BUG_ON(ahp->icv_trunc_len > MAX_AH_AUTH_LEN);

    if (x->props.flags & XFRM_STATE_ALIGN4)
        x->props.header_len = XFRM_ALIGN4(sizeof(struct ip_auth_hdr) +
                          ahp->icv_trunc_len);
    else
        x->props.header_len = XFRM_ALIGN8(sizeof(struct ip_auth_hdr) +
                          ahp->icv_trunc_len);
    if (x->props.mode == XFRM_MODE_TUNNEL)
        x->props.header_len += sizeof(struct iphdr);
    x->data = ahp;

    return 0;

error:
    if (ahp) {
        crypto_free_ahash(ahp->ahash);
        kfree(ahp);
    }
    return -EINVAL;
}

static void ah_destroy(struct xfrm_state *x)
{
    struct ah_data *ahp = x->data;

    if (!ahp)
        return;

    crypto_free_ahash(ahp->ahash);
    kfree(ahp);
}


static const struct xfrm_type ah_type =
{
    .description    = "AH4",
    .owner      = THIS_MODULE,
    .proto          = IPPROTO_AH,
    .flags      = XFRM_TYPE_REPLAY_PROT,
    .init_state = ah_init_state,
    .destructor = ah_destroy,
    .input      = ah_input,
    .output     = ah_output
};

static const struct net_protocol ah4_protocol = {
    .handler    =   xfrm4_rcv,
    .err_handler    =   ah4_err,
    .no_policy  =   1,
    .netns_ok   =   1,
};

static int __init ah4_init(void)
{
    if (xfrm_register_type(&ah_type, AF_INET) < 0) {
        pr_info("%s: can't add xfrm type\n", __func__);
        return -EAGAIN;
    }
    if (inet_add_protocol(&ah4_protocol, IPPROTO_AH) < 0) {
        pr_info("%s: can't add protocol\n", __func__);
        xfrm_unregister_type(&ah_type, AF_INET);
        return -EAGAIN;
    }
    return 0;
}

static void __exit ah4_fini(void)
{
    if (inet_del_protocol(&ah4_protocol, IPPROTO_AH) < 0)
        pr_info("%s: can't remove protocol\n", __func__);
    if (xfrm_unregister_type(&ah_type, AF_INET) < 0)
        pr_info("%s: can't remove xfrm type\n", __func__);
}

module_init(ah4_init);
module_exit(ah4_fini);
MODULE_LICENSE("GPL");
MODULE_ALIAS_XFRM_TYPE(AF_INET, XFRM_PROTO_AH);