[SCTP]: Implement SCTP-AUTH internals

This patch implements the internals operations of the AUTH, such as
key computation and storage.  It also adds necessary variables to
the SCTP data structures.

Signed-off-by: Vlad Yasevich <vladislav.yasevich@hp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 745 insertions, 0 deletions

diff --git a/net/sctp/auth.c b/net/sctp/auth.c
new file mode 100644
index 000000000000..2a29409a38d9
--- /dev/null
+++ b/net/sctp/auth.c
@@ -0,0 +1,745 @@
+/* SCTP kernel reference Implementation
+ * (C) Copyright 2007 Hewlett-Packard Development Company, L.P.
+ *
+ * This file is part of the SCTP kernel reference Implementation
+ *
+ * The SCTP reference implementation is free software;
+ * you can redistribute it and/or modify it under the terms of
+ * the GNU General Public License as published by
+ * the Free Software Foundation; either version 2, or (at your option)
+ * any later version.
+ *
+ * The SCTP reference implementation is distributed in the hope that it
+ * will be useful, but WITHOUT ANY WARRANTY; without even the implied
+ *                 ************************
+ * warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ * See the GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with GNU CC; see the file COPYING.  If not, write to
+ * the Free Software Foundation, 59 Temple Place - Suite 330,
+ * Boston, MA 02111-1307, USA.
+ *
+ * Please send any bug reports or fixes you make to the
+ * email address(es):
+ *    lksctp developers <lksctp-developers@lists.sourceforge.net>
+ *
+ * Or submit a bug report through the following website:
+ *    http://www.sf.net/projects/lksctp
+ *
+ * Written or modified by:
+ *   Vlad Yasevich     <vladislav.yasevich@hp.com>
+ *
+ * Any bugs reported given to us we will try to fix... any fixes shared will
+ * be incorporated into the next SCTP release.
+ */
+
+#include <linux/types.h>
+#include <linux/crypto.h>
+#include <linux/scatterlist.h>
+#include <net/sctp/sctp.h>
+#include <net/sctp/auth.h>
+
+static struct sctp_hmac sctp_hmac_list[SCTP_AUTH_NUM_HMACS] = {
+        {
+                /* id 0 is reserved.  as all 0 */
+                .hmac_id = SCTP_AUTH_HMAC_ID_RESERVED_0,
+        },
+        {
+                .hmac_id = SCTP_AUTH_HMAC_ID_SHA1,
+                .hmac_name="hmac(sha1)",
+                .hmac_len = SCTP_SHA1_SIG_SIZE,
+        },
+        {
+                /* id 2 is reserved as well */
+                .hmac_id = SCTP_AUTH_HMAC_ID_RESERVED_2,
+        },
+        {
+                .hmac_id = SCTP_AUTH_HMAC_ID_SHA256,
+                .hmac_name="hmac(sha256)",
+                .hmac_len = SCTP_SHA256_SIG_SIZE,
+        }
+};
+
+
+void sctp_auth_key_put(struct sctp_auth_bytes *key)
+{
+        if (!key)
+                return;
+
+        if (atomic_dec_and_test(&key->refcnt)) {
+                kfree(key);
+                SCTP_DBG_OBJCNT_DEC(keys);
+        }
+}
+
+/* Create a new key structure of a given length */
+static struct sctp_auth_bytes *sctp_auth_create_key(__u32 key_len, gfp_t gfp)
+{
+        struct sctp_auth_bytes *key;
+
+        /* Allocate the shared key */
+        key = kmalloc(sizeof(struct sctp_auth_bytes) + key_len, gfp);
+        if (!key)
+                return NULL;
+
+        key->len = key_len;
+        atomic_set(&key->refcnt, 1);
+        SCTP_DBG_OBJCNT_INC(keys);
+
+        return key;
+}
+
+/* Create a new shared key container with a give key id */
+struct sctp_shared_key *sctp_auth_shkey_create(__u16 key_id, gfp_t gfp)
+{
+        struct sctp_shared_key *new;
+
+        /* Allocate the shared key container */
+        new = kzalloc(sizeof(struct sctp_shared_key), gfp);
+        if (!new)
+                return NULL;
+
+        INIT_LIST_HEAD(&new->key_list);
+        new->key_id = key_id;
+
+        return new;
+}
+
+/* Free the shared key stucture */
+void sctp_auth_shkey_free(struct sctp_shared_key *sh_key)
+{
+        BUG_ON(!list_empty(&sh_key->key_list));
+        sctp_auth_key_put(sh_key->key);
+        sh_key->key = NULL;
+        kfree(sh_key);
+}
+
+/* Destory the entire key list.  This is done during the
+ * associon and endpoint free process.
+ */
+void sctp_auth_destroy_keys(struct list_head *keys)
+{
+        struct sctp_shared_key *ep_key;
+        struct sctp_shared_key *tmp;
+
+        if (list_empty(keys))
+                return;
+
+        key_for_each_safe(ep_key, tmp, keys) {
+                list_del_init(&ep_key->key_list);
+                sctp_auth_shkey_free(ep_key);
+        }
+}
+
+/* Compare two byte vectors as numbers.  Return values
+ * are:
+ *        0 - vectors are equal
+ *      < 0 - vector 1 is smaller then vector2
+ *      > 0 - vector 1 is greater then vector2
+ *
+ * Algorithm is:
+ *      This is performed by selecting the numerically smaller key vector...
+ *      If the key vectors are equal as numbers but differ in length ...
+ *      the shorter vector is considered smaller
+ *
+ * Examples (with small values):
+ *      000123456789 > 123456789 (first number is longer)
+ *      000123456789 < 234567891 (second number is larger numerically)
+ *      123456789 > 2345678      (first number is both larger & longer)
+ */
+static int sctp_auth_compare_vectors(struct sctp_auth_bytes *vector1,
+                              struct sctp_auth_bytes *vector2)
+{
+        int diff;
+        int i;
+        const __u8 *longer;
+
+        diff = vector1->len - vector2->len;
+        if (diff) {
+                longer = (diff > 0) ? vector1->data : vector2->data;
+
+                /* Check to see if the longer number is
+                 * lead-zero padded.  If it is not, it
+                 * is automatically larger numerically.
+                 */
+                for (i = 0; i < abs(diff); i++ ) {
+                        if (longer[i] != 0)
+                                return diff;
+                }
+        }
+
+        /* lengths are the same, compare numbers */
+        return memcmp(vector1->data, vector2->data, vector1->len);
+}
+
+/*
+ * Create a key vector as described in SCTP-AUTH, Section 6.1
+ *    The RANDOM parameter, the CHUNKS parameter and the HMAC-ALGO
+ *    parameter sent by each endpoint are concatenated as byte vectors.
+ *    These parameters include the parameter type, parameter length, and
+ *    the parameter value, but padding is omitted; all padding MUST be
+ *    removed from this concatenation before proceeding with further
+ *    computation of keys.  Parameters which were not sent are simply
+ *    omitted from the concatenation process.  The resulting two vectors
+ *    are called the two key vectors.
+ */
+static struct sctp_auth_bytes *sctp_auth_make_key_vector(
+                        sctp_random_param_t *random,
+                        sctp_chunks_param_t *chunks,
+                        sctp_hmac_algo_param_t *hmacs,
+                        gfp_t gfp)
+{
+        struct sctp_auth_bytes *new;
+        __u32   len;
+        __u32   offset = 0;
+
+        len = ntohs(random->param_hdr.length) + ntohs(hmacs->param_hdr.length);
+        if (chunks)
+                len += ntohs(chunks->param_hdr.length);
+
+        new = kmalloc(sizeof(struct sctp_auth_bytes) + len, gfp);
+        if (!new)
+                return NULL;
+
+        new->len = len;
+
+        memcpy(new->data, random, ntohs(random->param_hdr.length));
+        offset += ntohs(random->param_hdr.length);
+
+        if (chunks) {
+                memcpy(new->data + offset, chunks,
+                        ntohs(chunks->param_hdr.length));
+                offset += ntohs(chunks->param_hdr.length);
+        }
+
+        memcpy(new->data + offset, hmacs, ntohs(hmacs->param_hdr.length));
+
+        return new;
+}
+
+
+/* Make a key vector based on our local parameters */
+struct sctp_auth_bytes *sctp_auth_make_local_vector(
+                                    const struct sctp_association *asoc,
+                                    gfp_t gfp)
+{
+        return sctp_auth_make_key_vector(
+                                    (sctp_random_param_t*)asoc->c.auth_random,
+                                    (sctp_chunks_param_t*)asoc->c.auth_chunks,
+                                    (sctp_hmac_algo_param_t*)asoc->c.auth_hmacs,
+                                    gfp);
+}
+
+/* Make a key vector based on peer's parameters */
+struct sctp_auth_bytes *sctp_auth_make_peer_vector(
+                                    const struct sctp_association *asoc,
+                                    gfp_t gfp)
+{
+        return sctp_auth_make_key_vector(asoc->peer.peer_random,
+                                         asoc->peer.peer_chunks,
+                                         asoc->peer.peer_hmacs,
+                                         gfp);
+}
+
+
+/* Set the value of the association shared key base on the parameters
+ * given.  The algorithm is:
+ *    From the endpoint pair shared keys and the key vectors the
+ *    association shared keys are computed.  This is performed by selecting
+ *    the numerically smaller key vector and concatenating it to the
+ *    endpoint pair shared key, and then concatenating the numerically
+ *    larger key vector to that.  The result of the concatenation is the
+ *    association shared key.
+ */
+static struct sctp_auth_bytes *sctp_auth_asoc_set_secret(
+                        struct sctp_shared_key *ep_key,
+                        struct sctp_auth_bytes *first_vector,
+                        struct sctp_auth_bytes *last_vector,
+                        gfp_t gfp)
+{
+        struct sctp_auth_bytes *secret;
+        __u32 offset = 0;
+        __u32 auth_len;
+
+        auth_len = first_vector->len + last_vector->len;
+        if (ep_key->key)
+                auth_len += ep_key->key->len;
+
+        secret = sctp_auth_create_key(auth_len, gfp);
+        if (!secret)
+                return NULL;
+
+        if (ep_key->key) {
+                memcpy(secret->data, ep_key->key->data, ep_key->key->len);
+                offset += ep_key->key->len;
+        }
+
+        memcpy(secret->data + offset, first_vector->data, first_vector->len);
+        offset += first_vector->len;
+
+        memcpy(secret->data + offset, last_vector->data, last_vector->len);
+
+        return secret;
+}
+
+/* Create an association shared key.  Follow the algorithm
+ * described in SCTP-AUTH, Section 6.1
+ */
+static struct sctp_auth_bytes *sctp_auth_asoc_create_secret(
+                                 const struct sctp_association *asoc,
+                                 struct sctp_shared_key *ep_key,
+                                 gfp_t gfp)
+{
+        struct sctp_auth_bytes *local_key_vector;
+        struct sctp_auth_bytes *peer_key_vector;
+        struct sctp_auth_bytes  *first_vector,
+                                *last_vector;
+        struct sctp_auth_bytes  *secret = NULL;
+        int     cmp;
+
+
+        /* Now we need to build the key vectors
+         * SCTP-AUTH , Section 6.1
+         *    The RANDOM parameter, the CHUNKS parameter and the HMAC-ALGO
+         *    parameter sent by each endpoint are concatenated as byte vectors.
+         *    These parameters include the parameter type, parameter length, and
+         *    the parameter value, but padding is omitted; all padding MUST be
+         *    removed from this concatenation before proceeding with further
+         *    computation of keys.  Parameters which were not sent are simply
+         *    omitted from the concatenation process.  The resulting two vectors
+         *    are called the two key vectors.
+         */
+
+        local_key_vector = sctp_auth_make_local_vector(asoc, gfp);
+        peer_key_vector = sctp_auth_make_peer_vector(asoc, gfp);
+
+        if (!peer_key_vector || !local_key_vector)
+                goto out;
+
+        /* Figure out the order in wich the key_vectors will be
+         * added to the endpoint shared key.
+         * SCTP-AUTH, Section 6.1:
+         *   This is performed by selecting the numerically smaller key
+         *   vector and concatenating it to the endpoint pair shared
+         *   key, and then concatenating the numerically larger key
+         *   vector to that.  If the key vectors are equal as numbers
+         *   but differ in length, then the concatenation order is the
+         *   endpoint shared key, followed by the shorter key vector,
+         *   followed by the longer key vector.  Otherwise, the key
+         *   vectors are identical, and may be concatenated to the
+         *   endpoint pair key in any order.
+         */
+        cmp = sctp_auth_compare_vectors(local_key_vector,
+                                        peer_key_vector);
+        if (cmp < 0) {
+                first_vector = local_key_vector;
+                last_vector = peer_key_vector;
+        } else {
+                first_vector = peer_key_vector;
+                last_vector = local_key_vector;
+        }
+
+        secret = sctp_auth_asoc_set_secret(ep_key, first_vector, last_vector,
+                                            gfp);
+out:
+        kfree(local_key_vector);
+        kfree(peer_key_vector);
+
+        return secret;
+}
+
+/*
+ * Populate the association overlay list with the list
+ * from the endpoint.
+ */
+int sctp_auth_asoc_copy_shkeys(const struct sctp_endpoint *ep,
+                                struct sctp_association *asoc,
+                                gfp_t gfp)
+{
+        struct sctp_shared_key *sh_key;
+        struct sctp_shared_key *new;
+
+        BUG_ON(!list_empty(&asoc->endpoint_shared_keys));
+
+        key_for_each(sh_key, &ep->endpoint_shared_keys) {
+                new = sctp_auth_shkey_create(sh_key->key_id, gfp);
+                if (!new)
+                        goto nomem;
+
+                new->key = sh_key->key;
+                sctp_auth_key_hold(new->key);
+                list_add(&new->key_list, &asoc->endpoint_shared_keys);
+        }
+
+        return 0;
+
+nomem:
+        sctp_auth_destroy_keys(&asoc->endpoint_shared_keys);
+        return -ENOMEM;
+}
+
+
+/* Public interface to creat the association shared key.
+ * See code above for the algorithm.
+ */
+int sctp_auth_asoc_init_active_key(struct sctp_association *asoc, gfp_t gfp)
+{
+        struct sctp_auth_bytes  *secret;
+        struct sctp_shared_key *ep_key;
+
+        /* If we don't support AUTH, or peer is not capable
+         * we don't need to do anything.
+         */
+        if (!sctp_auth_enable || !asoc->peer.auth_capable)
+                return 0;
+
+        /* If the key_id is non-zero and we couldn't find an
+         * endpoint pair shared key, we can't compute the
+         * secret.
+         * For key_id 0, endpoint pair shared key is a NULL key.
+         */
+        ep_key = sctp_auth_get_shkey(asoc, asoc->active_key_id);
+        BUG_ON(!ep_key);
+
+        secret = sctp_auth_asoc_create_secret(asoc, ep_key, gfp);
+        if (!secret)
+                return -ENOMEM;
+
+        sctp_auth_key_put(asoc->asoc_shared_key);
+        asoc->asoc_shared_key = secret;
+
+        return 0;
+}
+
+
+/* Find the endpoint pair shared key based on the key_id */
+struct sctp_shared_key *sctp_auth_get_shkey(
+                                const struct sctp_association *asoc,
+                                __u16 key_id)
+{
+        struct sctp_shared_key *key = NULL;
+
+        /* First search associations set of endpoint pair shared keys */
+        key_for_each(key, &asoc->endpoint_shared_keys) {
+                if (key->key_id == key_id)
+                        break;
+        }
+
+        return key;
+}
+
+/*
+ * Initialize all the possible digest transforms that we can use.  Right now
+ * now, the supported digests are SHA1 and SHA256.  We do this here once
+ * because of the restrictiong that transforms may only be allocated in
+ * user context.  This forces us to pre-allocated all possible transforms
+ * at the endpoint init time.
+ */
+int sctp_auth_init_hmacs(struct sctp_endpoint *ep, gfp_t gfp)
+{
+        struct crypto_hash *tfm = NULL;
+        __u16   id;
+
+        /* if the transforms are already allocted, we are done */
+        if (!sctp_auth_enable) {
+                ep->auth_hmacs = NULL;
+                return 0;
+        }
+
+        if (ep->auth_hmacs)
+                return 0;
+
+        /* Allocated the array of pointers to transorms */
+        ep->auth_hmacs = kzalloc(
+                            sizeof(struct crypto_hash *) * SCTP_AUTH_NUM_HMACS,
+                            gfp);
+        if (!ep->auth_hmacs)
+                return -ENOMEM;
+
+        for (id = 0; id < SCTP_AUTH_NUM_HMACS; id++) {
+
+                /* See is we support the id.  Supported IDs have name and
+                 * length fields set, so that we can allocated and use
+                 * them.  We can safely just check for name, for without the
+                 * name, we can't allocate the TFM.
+                 */
+                if (!sctp_hmac_list[id].hmac_name)
+                        continue;
+
+                /* If this TFM has been allocated, we are all set */
+                if (ep->auth_hmacs[id])
+                        continue;
+
+                /* Allocate the ID */
+                tfm = crypto_alloc_hash(sctp_hmac_list[id].hmac_name, 0,
+                                        CRYPTO_ALG_ASYNC);
+                if (IS_ERR(tfm))
+                        goto out_err;
+
+                ep->auth_hmacs[id] = tfm;
+        }
+
+        return 0;
+
+out_err:
+        /* Clean up any successfull allocations */
+        sctp_auth_destroy_hmacs(ep->auth_hmacs);
+        return -ENOMEM;
+}
+
+/* Destroy the hmac tfm array */
+void sctp_auth_destroy_hmacs(struct crypto_hash *auth_hmacs[])
+{
+        int i;
+
+        if (!auth_hmacs)
+                return;
+
+        for (i = 0; i < SCTP_AUTH_NUM_HMACS; i++)
+        {
+                if (auth_hmacs[i])
+                        crypto_free_hash(auth_hmacs[i]);
+        }
+        kfree(auth_hmacs);
+}
+
+
+struct sctp_hmac *sctp_auth_get_hmac(__u16 hmac_id)
+{
+        return &sctp_hmac_list[hmac_id];
+}
+
+/* Get an hmac description information that we can use to build
+ * the AUTH chunk
+ */
+struct sctp_hmac *sctp_auth_asoc_get_hmac(const struct sctp_association *asoc)
+{
+        struct sctp_hmac_algo_param *hmacs;
+        __u16 n_elt;
+        __u16 id = 0;
+        int i;
+
+        /* If we have a default entry, use it */
+        if (asoc->default_hmac_id)
+                return &sctp_hmac_list[asoc->default_hmac_id];
+
+        /* Since we do not have a default entry, find the first entry
+         * we support and return that.  Do not cache that id.
+         */
+        hmacs = asoc->peer.peer_hmacs;
+        if (!hmacs)
+                return NULL;
+
+        n_elt = (ntohs(hmacs->param_hdr.length) - sizeof(sctp_paramhdr_t)) >> 1;
+        for (i = 0; i < n_elt; i++) {
+                id = ntohs(hmacs->hmac_ids[i]);
+
+                /* Check the id is in the supported range */
+                if (id > SCTP_AUTH_HMAC_ID_MAX)
+                        continue;
+
+                /* See is we support the id.  Supported IDs have name and
+                 * length fields set, so that we can allocated and use
+                 * them.  We can safely just check for name, for without the
+                 * name, we can't allocate the TFM.
+                 */
+                if (!sctp_hmac_list[id].hmac_name)
+                        continue;
+
+                break;
+        }
+
+        if (id == 0)
+                return NULL;
+
+        return &sctp_hmac_list[id];
+}
+
+static int __sctp_auth_find_hmacid(__u16 *hmacs, int n_elts, __u16 hmac_id)
+{
+        int  found = 0;
+        int  i;
+
+        for (i = 0; i < n_elts; i++) {
+                if (hmac_id == hmacs[i]) {
+                        found = 1;
+                        break;
+                }
+        }
+
+        return found;
+}
+
+/* See if the HMAC_ID is one that we claim as supported */
+int sctp_auth_asoc_verify_hmac_id(const struct sctp_association *asoc,
+                                    __u16 hmac_id)
+{
+        struct sctp_hmac_algo_param *hmacs;
+        __u16 n_elt;
+
+        if (!asoc)
+                return 0;
+
+        hmacs = (struct sctp_hmac_algo_param *)asoc->c.auth_hmacs;
+        n_elt = (ntohs(hmacs->param_hdr.length) - sizeof(sctp_paramhdr_t)) >> 1;
+
+        return __sctp_auth_find_hmacid(hmacs->hmac_ids, n_elt, hmac_id);
+}
+
+
+/* Cache the default HMAC id.  This to follow this text from SCTP-AUTH:
+ * Section 6.1:
+ *   The receiver of a HMAC-ALGO parameter SHOULD use the first listed
+ *   algorithm it supports.
+ */
+void sctp_auth_asoc_set_default_hmac(struct sctp_association *asoc,
+                                     struct sctp_hmac_algo_param *hmacs)
+{
+        struct sctp_endpoint *ep;
+        __u16   id;
+        int     i;
+        int     n_params;
+
+        /* if the default id is already set, use it */
+        if (asoc->default_hmac_id)
+                return;
+
+        n_params = (ntohs(hmacs->param_hdr.length)
+                                - sizeof(sctp_paramhdr_t)) >> 1;
+        ep = asoc->ep;
+        for (i = 0; i < n_params; i++) {
+                id = ntohs(hmacs->hmac_ids[i]);
+
+                /* Check the id is in the supported range */
+                if (id > SCTP_AUTH_HMAC_ID_MAX)
+                        continue;
+
+                /* If this TFM has been allocated, use this id */
+                if (ep->auth_hmacs[id]) {
+                        asoc->default_hmac_id = id;
+                        break;
+                }
+        }
+}
+
+
+/* Check to see if the given chunk is supposed to be authenticated */
+static int __sctp_auth_cid(sctp_cid_t chunk, struct sctp_chunks_param *param)
+{
+        unsigned short len;
+        int found = 0;
+        int i;
+
+        if (!param)
+                return 0;
+
+        len = ntohs(param->param_hdr.length) - sizeof(sctp_paramhdr_t);
+
+        /* SCTP-AUTH, Section 3.2
+         *    The chunk types for INIT, INIT-ACK, SHUTDOWN-COMPLETE and AUTH
+         *    chunks MUST NOT be listed in the CHUNKS parameter.  However, if
+         *    a CHUNKS parameter is received then the types for INIT, INIT-ACK,
+         *    SHUTDOWN-COMPLETE and AUTH chunks MUST be ignored.
+         */
+        for (i = 0; !found && i < len; i++) {
+                switch (param->chunks[i]) {
+                    case SCTP_CID_INIT:
+                    case SCTP_CID_INIT_ACK:
+                    case SCTP_CID_SHUTDOWN_COMPLETE:
+                    case SCTP_CID_AUTH:
+                        break;
+
+                    default:
+                        if (param->chunks[i] == chunk)
+                            found = 1;
+                        break;
+                }
+        }
+
+        return found;
+}
+
+/* Check if peer requested that this chunk is authenticated */
+int sctp_auth_send_cid(sctp_cid_t chunk, const struct sctp_association *asoc)
+{
+        if (!sctp_auth_enable || !asoc || !asoc->peer.auth_capable)
+                return 0;
+
+        return __sctp_auth_cid(chunk, asoc->peer.peer_chunks);
+}
+
+/* Check if we requested that peer authenticate this chunk. */
+int sctp_auth_recv_cid(sctp_cid_t chunk, const struct sctp_association *asoc)
+{
+        if (!sctp_auth_enable || !asoc)
+                return 0;
+
+        return __sctp_auth_cid(chunk,
+                              (struct sctp_chunks_param *)asoc->c.auth_chunks);
+}
+
+/* SCTP-AUTH: Section 6.2:
+ *    The sender MUST calculate the MAC as described in RFC2104 [2] using
+ *    the hash function H as described by the MAC Identifier and the shared
+ *    association key K based on the endpoint pair shared key described by
+ *    the shared key identifier.  The 'data' used for the computation of
+ *    the AUTH-chunk is given by the AUTH chunk with its HMAC field set to
+ *    zero (as shown in Figure 6) followed by all chunks that are placed
+ *    after the AUTH chunk in the SCTP packet.
+ */
+void sctp_auth_calculate_hmac(const struct sctp_association *asoc,
+                              struct sk_buff *skb,
+                              struct sctp_auth_chunk *auth,
+                              gfp_t gfp)
+{
+        struct scatterlist sg;
+        struct hash_desc desc;
+        struct sctp_auth_bytes *asoc_key;
+        __u16 key_id, hmac_id;
+        __u8 *digest;
+        unsigned char *end;
+        int free_key = 0;
+
+        /* Extract the info we need:
+         * - hmac id
+         * - key id
+         */
+        key_id = ntohs(auth->auth_hdr.shkey_id);
+        hmac_id = ntohs(auth->auth_hdr.hmac_id);
+
+        if (key_id == asoc->active_key_id)
+                asoc_key = asoc->asoc_shared_key;
+        else {
+                struct sctp_shared_key *ep_key;
+
+                ep_key = sctp_auth_get_shkey(asoc, key_id);
+                if (!ep_key)
+                        return;
+
+                asoc_key = sctp_auth_asoc_create_secret(asoc, ep_key, gfp);
+                if (!asoc_key)
+                        return;
+
+                free_key = 1;
+        }
+
+        /* set up scatter list */
+        end = skb_tail_pointer(skb);
+        sg.page = virt_to_page(auth);
+        sg.offset = (unsigned long)(auth) % PAGE_SIZE;
+        sg.length = end - (unsigned char *)auth;
+
+        desc.tfm = asoc->ep->auth_hmacs[hmac_id];
+        desc.flags = 0;
+
+        digest = auth->auth_hdr.hmac;
+        if (crypto_hash_setkey(desc.tfm, &asoc_key->data[0], asoc_key->len))
+                goto free;
+
+        crypto_hash_digest(&desc, &sg, sg.length, digest);
+
+free:
+        if (free_key)
+                sctp_auth_key_put(asoc_key);
+}