RPCSEC_GSS: Add support for privacy to krb5 rpcsec_gss mechanism.

 Add support for privacy to the krb5 rpcsec_gss mechanism.

 Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
 Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

7 files changed, 552 insertions, 7 deletions

diff --git a/include/linux/sunrpc/gss_krb5.h b/include/linux/sunrpc/gss_krb5.h
index cb35833e2ae3..7f93c2d5ebdb 100644
--- a/include/linux/sunrpc/gss_krb5.h
+++ b/include/linux/sunrpc/gss_krb5.h
@@ -116,7 +116,7 @@ enum seal_alg {
 
 s32
 make_checksum(s32 cksumtype, char *header, int hdrlen, struct xdr_buf *body,
-                   struct xdr_netobj *cksum);
+                   int body_offset, struct xdr_netobj *cksum);
 
 u32
 krb5_make_token(struct krb5_ctx *context_handle, int qop_req,
@@ -129,6 +129,15 @@ krb5_read_token(struct krb5_ctx *context_handle,
           struct xdr_buf *message_buffer, int *qop_state);
 
 u32
+gss_wrap_kerberos(struct gss_ctx *ctx_id, u32 qop, int offset,
+                struct xdr_buf *outbuf, struct page **pages);
+
+u32
+gss_unwrap_kerberos(struct gss_ctx *ctx_id, u32 *qop, int offset,
+                struct xdr_buf *buf);
+
+
+u32
 krb5_encrypt(struct crypto_tfm * key,
              void *iv, void *in, void *out, int length);
 
@@ -136,6 +145,13 @@ u32
 krb5_decrypt(struct crypto_tfm * key,
              void *iv, void *in, void *out, int length); 
 
+int
+gss_encrypt_xdr_buf(struct crypto_tfm *tfm, struct xdr_buf *outbuf, int offset,
+                struct page **pages);
+
+int
+gss_decrypt_xdr_buf(struct crypto_tfm *tfm, struct xdr_buf *inbuf, int offset);
+
 s32
 krb5_make_seq_num(struct crypto_tfm * key,
                 int direction,
diff --git a/net/sunrpc/auth_gss/Makefile b/net/sunrpc/auth_gss/Makefile
index fe1b874084bc..f3431a7e33da 100644
--- a/net/sunrpc/auth_gss/Makefile
+++ b/net/sunrpc/auth_gss/Makefile
@@ -10,7 +10,7 @@ auth_rpcgss-objs := auth_gss.o gss_generic_token.o \
 obj-$(CONFIG_RPCSEC_GSS_KRB5) += rpcsec_gss_krb5.o
 
 rpcsec_gss_krb5-objs := gss_krb5_mech.o gss_krb5_seal.o gss_krb5_unseal.o \
-        gss_krb5_seqnum.o
+        gss_krb5_seqnum.o gss_krb5_wrap.o
 
 obj-$(CONFIG_RPCSEC_GSS_SPKM3) += rpcsec_gss_spkm3.o
 
diff --git a/net/sunrpc/auth_gss/gss_krb5_crypto.c b/net/sunrpc/auth_gss/gss_krb5_crypto.c
index 2baf93f8b8f5..3f3d5437f02d 100644
--- a/net/sunrpc/auth_gss/gss_krb5_crypto.c
+++ b/net/sunrpc/auth_gss/gss_krb5_crypto.c
@@ -218,7 +218,7 @@ checksummer(struct scatterlist *sg, void *data)
 /* checksum the plaintext data and hdrlen bytes of the token header */
 s32
 make_checksum(s32 cksumtype, char *header, int hdrlen, struct xdr_buf *body,
-                   struct xdr_netobj *cksum)
+                   int body_offset, struct xdr_netobj *cksum)
 {
         char                            *cksumname;
         struct crypto_tfm               *tfm = NULL; /* XXX add to ctx? */
@@ -243,7 +243,8 @@ make_checksum(s32 cksumtype, char *header, int hdrlen, struct xdr_buf *body,
         crypto_digest_init(tfm);
         buf_to_sg(sg, header, hdrlen);
         crypto_digest_update(tfm, sg, 1);
-        process_xdr_buf(body, 0, body->len, checksummer, tfm);
+        process_xdr_buf(body, body_offset, body->len - body_offset,
+                        checksummer, tfm);
         crypto_digest_final(tfm, cksum->data);
         code = 0;
 out:
@@ -252,3 +253,154 @@ out:
 }
 
 EXPORT_SYMBOL(make_checksum);
+
+struct encryptor_desc {
+        u8 iv[8]; /* XXX hard-coded blocksize */
+        struct crypto_tfm *tfm;
+        int pos;
+        struct xdr_buf *outbuf;
+        struct page **pages;
+        struct scatterlist infrags[4];
+        struct scatterlist outfrags[4];
+        int fragno;
+        int fraglen;
+};
+
+static int
+encryptor(struct scatterlist *sg, void *data)
+{
+        struct encryptor_desc *desc = data;
+        struct xdr_buf *outbuf = desc->outbuf;
+        struct page *in_page;
+        int thislen = desc->fraglen + sg->length;
+        int fraglen, ret;
+        int page_pos;
+
+        /* Worst case is 4 fragments: head, end of page 1, start
+         * of page 2, tail.  Anything more is a bug. */
+        BUG_ON(desc->fragno > 3);
+        desc->infrags[desc->fragno] = *sg;
+        desc->outfrags[desc->fragno] = *sg;
+
+        page_pos = desc->pos - outbuf->head[0].iov_len;
+        if (page_pos >= 0 && page_pos < outbuf->page_len) {
+                /* pages are not in place: */
+                int i = (page_pos + outbuf->page_base) >> PAGE_CACHE_SHIFT;
+                in_page = desc->pages[i];
+        } else {
+                in_page = sg->page;
+        }
+        desc->infrags[desc->fragno].page = in_page;
+        desc->fragno++;
+        desc->fraglen += sg->length;
+        desc->pos += sg->length;
+
+        fraglen = thislen & 7; /* XXX hardcoded blocksize */
+        thislen -= fraglen;
+
+        if (thislen == 0)
+                return 0;
+
+        ret = crypto_cipher_encrypt_iv(desc->tfm, desc->outfrags, desc->infrags,
+                                        thislen, desc->iv);
+        if (ret)
+                return ret;
+        if (fraglen) {
+                desc->outfrags[0].page = sg->page;
+                desc->outfrags[0].offset = sg->offset + sg->length - fraglen;
+                desc->outfrags[0].length = fraglen;
+                desc->infrags[0] = desc->outfrags[0];
+                desc->infrags[0].page = in_page;
+                desc->fragno = 1;
+                desc->fraglen = fraglen;
+        } else {
+                desc->fragno = 0;
+                desc->fraglen = 0;
+        }
+        return 0;
+}
+
+int
+gss_encrypt_xdr_buf(struct crypto_tfm *tfm, struct xdr_buf *buf, int offset,
+                struct page **pages)
+{
+        int ret;
+        struct encryptor_desc desc;
+
+        BUG_ON((buf->len - offset) % crypto_tfm_alg_blocksize(tfm) != 0);
+
+        memset(desc.iv, 0, sizeof(desc.iv));
+        desc.tfm = tfm;
+        desc.pos = offset;
+        desc.outbuf = buf;
+        desc.pages = pages;
+        desc.fragno = 0;
+        desc.fraglen = 0;
+
+        ret = process_xdr_buf(buf, offset, buf->len - offset, encryptor, &desc);
+        return ret;
+}
+
+EXPORT_SYMBOL(gss_encrypt_xdr_buf);
+
+struct decryptor_desc {
+        u8 iv[8]; /* XXX hard-coded blocksize */
+        struct crypto_tfm *tfm;
+        struct scatterlist frags[4];
+        int fragno;
+        int fraglen;
+};
+
+static int
+decryptor(struct scatterlist *sg, void *data)
+{
+        struct decryptor_desc *desc = data;
+        int thislen = desc->fraglen + sg->length;
+        int fraglen, ret;
+
+        /* Worst case is 4 fragments: head, end of page 1, start
+         * of page 2, tail.  Anything more is a bug. */
+        BUG_ON(desc->fragno > 3);
+        desc->frags[desc->fragno] = *sg;
+        desc->fragno++;
+        desc->fraglen += sg->length;
+
+        fraglen = thislen & 7; /* XXX hardcoded blocksize */
+        thislen -= fraglen;
+
+        if (thislen == 0)
+                return 0;
+
+        ret = crypto_cipher_decrypt_iv(desc->tfm, desc->frags, desc->frags,
+                                        thislen, desc->iv);
+        if (ret)
+                return ret;
+        if (fraglen) {
+                desc->frags[0].page = sg->page;
+                desc->frags[0].offset = sg->offset + sg->length - fraglen;
+                desc->frags[0].length = fraglen;
+                desc->fragno = 1;
+                desc->fraglen = fraglen;
+        } else {
+                desc->fragno = 0;
+                desc->fraglen = 0;
+        }
+        return 0;
+}
+
+int
+gss_decrypt_xdr_buf(struct crypto_tfm *tfm, struct xdr_buf *buf, int offset)
+{
+        struct decryptor_desc desc;
+
+        /* XXXJBF: */
+        BUG_ON((buf->len - offset) % crypto_tfm_alg_blocksize(tfm) != 0);
+
+        memset(desc.iv, 0, sizeof(desc.iv));
+        desc.tfm = tfm;
+        desc.fragno = 0;
+        desc.fraglen = 0;
+        return process_xdr_buf(buf, offset, buf->len - offset, decryptor, &desc);
+}
+
+EXPORT_SYMBOL(gss_decrypt_xdr_buf);
diff --git a/net/sunrpc/auth_gss/gss_krb5_mech.c b/net/sunrpc/auth_gss/gss_krb5_mech.c
index 8b9066fdfda5..37a9ad97ccd4 100644
--- a/net/sunrpc/auth_gss/gss_krb5_mech.c
+++ b/net/sunrpc/auth_gss/gss_krb5_mech.c
@@ -226,6 +226,8 @@ static struct gss_api_ops gss_kerberos_ops = {
         .gss_import_sec_context = gss_import_sec_context_kerberos,
         .gss_get_mic            = gss_get_mic_kerberos,
         .gss_verify_mic         = gss_verify_mic_kerberos,
+        .gss_wrap               = gss_wrap_kerberos,
+        .gss_unwrap             = gss_unwrap_kerberos,
         .gss_delete_sec_context = gss_delete_sec_context_kerberos,
 };
 
@@ -240,6 +242,11 @@ static struct pf_desc gss_kerberos_pfs[] = {
                 .service = RPC_GSS_SVC_INTEGRITY,
                 .name = "krb5i",
         },
+        [2] = {
+                .pseudoflavor = RPC_AUTH_GSS_KRB5P,
+                .service = RPC_GSS_SVC_PRIVACY,
+                .name = "krb5p",
+        },
 };
 
 static struct gss_api_mech gss_kerberos_mech = {
diff --git a/net/sunrpc/auth_gss/gss_krb5_seal.c b/net/sunrpc/auth_gss/gss_krb5_seal.c
index 2511834e6e52..fb852d9ab06f 100644
--- a/net/sunrpc/auth_gss/gss_krb5_seal.c
+++ b/net/sunrpc/auth_gss/gss_krb5_seal.c
@@ -116,8 +116,8 @@ krb5_make_token(struct krb5_ctx *ctx, int qop_req,
         *(u16 *)(krb5_hdr + 2) = htons(ctx->signalg);
         memset(krb5_hdr + 4, 0xff, 4);
 
-        if (make_checksum(checksum_type, krb5_hdr, 8, text, &md5cksum))
-                goto out_err;
+        if (make_checksum(checksum_type, krb5_hdr, 8, text, 0, &md5cksum))
+                        goto out_err;
 
         switch (ctx->signalg) {
         case SGN_ALG_DES_MAC_MD5:
diff --git a/net/sunrpc/auth_gss/gss_krb5_unseal.c b/net/sunrpc/auth_gss/gss_krb5_unseal.c
index 19eba3df6607..c3d6d1bc100c 100644
--- a/net/sunrpc/auth_gss/gss_krb5_unseal.c
+++ b/net/sunrpc/auth_gss/gss_krb5_unseal.c
@@ -136,7 +136,7 @@ krb5_read_token(struct krb5_ctx *ctx,
         switch (signalg) {
         case SGN_ALG_DES_MAC_MD5:
                 ret = make_checksum(checksum_type, ptr - 2, 8,
-                                         message_buffer, &md5cksum);
+                                         message_buffer, 0, &md5cksum);
                 if (ret)
                         goto out;
 
diff --git a/net/sunrpc/auth_gss/gss_krb5_wrap.c b/net/sunrpc/auth_gss/gss_krb5_wrap.c
new file mode 100644
index 000000000000..ddcde6e42b23
--- /dev/null
+++ b/net/sunrpc/auth_gss/gss_krb5_wrap.c
@@ -0,0 +1,370 @@
+#include <linux/types.h>
+#include <linux/slab.h>
+#include <linux/jiffies.h>
+#include <linux/sunrpc/gss_krb5.h>
+#include <linux/random.h>
+#include <linux/pagemap.h>
+#include <asm/scatterlist.h>
+#include <linux/crypto.h>
+
+#ifdef RPC_DEBUG
+# define RPCDBG_FACILITY        RPCDBG_AUTH
+#endif
+
+static inline int
+gss_krb5_padding(int blocksize, int length)
+{
+        /* Most of the code is block-size independent but currently we
+         * use only 8: */
+        BUG_ON(blocksize != 8);
+        return 8 - (length & 7);
+}
+
+static inline void
+gss_krb5_add_padding(struct xdr_buf *buf, int offset, int blocksize)
+{
+        int padding = gss_krb5_padding(blocksize, buf->len - offset);
+        char *p;
+        struct kvec *iov;
+
+        if (buf->page_len || buf->tail[0].iov_len)
+                iov = &buf->tail[0];
+        else
+                iov = &buf->head[0];
+        p = iov->iov_base + iov->iov_len;
+        iov->iov_len += padding;
+        buf->len += padding;
+        memset(p, padding, padding);
+}
+
+static inline int
+gss_krb5_remove_padding(struct xdr_buf *buf, int blocksize)
+{
+        u8 *ptr;
+        u8 pad;
+        int len = buf->len;
+
+        if (len <= buf->head[0].iov_len) {
+                pad = *(u8 *)(buf->head[0].iov_base + len - 1);
+                if (pad > buf->head[0].iov_len)
+                        return -EINVAL;
+                buf->head[0].iov_len -= pad;
+                goto out;
+        } else
+                len -= buf->head[0].iov_len;
+        if (len <= buf->page_len) {
+                int last = (buf->page_base + len - 1)
+                                        >>PAGE_CACHE_SHIFT;
+                int offset = (buf->page_base + len - 1)
+                                        & (PAGE_CACHE_SIZE - 1);
+                ptr = kmap_atomic(buf->pages[last], KM_SKB_SUNRPC_DATA);
+                pad = *(ptr + offset);
+                kunmap_atomic(ptr, KM_SKB_SUNRPC_DATA);
+                goto out;
+        } else
+                len -= buf->page_len;
+        BUG_ON(len > buf->tail[0].iov_len);
+        pad = *(u8 *)(buf->tail[0].iov_base + len - 1);
+out:
+        /* XXX: NOTE: we do not adjust the page lengths--they represent
+         * a range of data in the real filesystem page cache, and we need
+         * to know that range so the xdr code can properly place read data.
+         * However adjusting the head length, as we do above, is harmless.
+         * In the case of a request that fits into a single page, the server
+         * also uses length and head length together to determine the original
+         * start of the request to copy the request for deferal; so it's
+         * easier on the server if we adjust head and tail length in tandem.
+         * It's not really a problem that we don't fool with the page and
+         * tail lengths, though--at worst badly formed xdr might lead the
+         * server to attempt to parse the padding.
+         * XXX: Document all these weird requirements for gss mechanism
+         * wrap/unwrap functions. */
+        if (pad > blocksize)
+                return -EINVAL;
+        if (buf->len > pad)
+                buf->len -= pad;
+        else
+                return -EINVAL;
+        return 0;
+}
+
+static inline void
+make_confounder(char *p, int blocksize)
+{
+        static u64 i = 0;
+        u64 *q = (u64 *)p;
+
+        /* rfc1964 claims this should be "random".  But all that's really
+         * necessary is that it be unique.  And not even that is necessary in
+         * our case since our "gssapi" implementation exists only to support
+         * rpcsec_gss, so we know that the only buffers we will ever encrypt
+         * already begin with a unique sequence number.  Just to hedge my bets
+         * I'll make a half-hearted attempt at something unique, but ensuring
+         * uniqueness would mean worrying about atomicity and rollover, and I
+         * don't care enough. */
+
+        BUG_ON(blocksize != 8);
+        *q = i++;
+}
+
+/* Assumptions: the head and tail of inbuf are ours to play with.
+ * The pages, however, may be real pages in the page cache and we replace
+ * them with scratch pages from **pages before writing to them. */
+/* XXX: obviously the above should be documentation of wrap interface,
+ * and shouldn't be in this kerberos-specific file. */
+
+/* XXX factor out common code with seal/unseal. */
+
+u32
+gss_wrap_kerberos(struct gss_ctx *ctx, u32 qop, int offset,
+                struct xdr_buf *buf, struct page **pages)
+{
+        struct krb5_ctx         *kctx = ctx->internal_ctx_id;
+        s32                     checksum_type;
+        struct xdr_netobj       md5cksum = {.len = 0, .data = NULL};
+        int                     blocksize = 0, plainlen;
+        unsigned char           *ptr, *krb5_hdr, *msg_start;
+        s32                     now;
+        int                     headlen;
+        struct page             **tmp_pages;
+
+        dprintk("RPC:     gss_wrap_kerberos\n");
+
+        now = get_seconds();
+
+        if (qop != 0)
+                goto out_err;
+
+        switch (kctx->signalg) {
+                case SGN_ALG_DES_MAC_MD5:
+                        checksum_type = CKSUMTYPE_RSA_MD5;
+                        break;
+                default:
+                        dprintk("RPC:      gss_krb5_seal: kctx->signalg %d not"
+                                " supported\n", kctx->signalg);
+                        goto out_err;
+        }
+        if (kctx->sealalg != SEAL_ALG_NONE && kctx->sealalg != SEAL_ALG_DES) {
+                dprintk("RPC:      gss_krb5_seal: kctx->sealalg %d not supported\n",
+                        kctx->sealalg);
+                goto out_err;
+        }
+
+        blocksize = crypto_tfm_alg_blocksize(kctx->enc);
+        gss_krb5_add_padding(buf, offset, blocksize);
+        BUG_ON((buf->len - offset) % blocksize);
+        plainlen = blocksize + buf->len - offset;
+
+        headlen = g_token_size(&kctx->mech_used, 22 + plainlen) -
+                                                (buf->len - offset);
+
+        ptr = buf->head[0].iov_base + offset;
+        /* shift data to make room for header. */
+        /* XXX Would be cleverer to encrypt while copying. */
+        /* XXX bounds checking, slack, etc. */
+        memmove(ptr + headlen, ptr, buf->head[0].iov_len - offset);
+        buf->head[0].iov_len += headlen;
+        buf->len += headlen;
+        BUG_ON((buf->len - offset - headlen) % blocksize);
+
+        g_make_token_header(&kctx->mech_used, 22 + plainlen, &ptr);
+
+
+        *ptr++ = (unsigned char) ((KG_TOK_WRAP_MSG>>8)&0xff);
+        *ptr++ = (unsigned char) (KG_TOK_WRAP_MSG&0xff);
+
+        /* ptr now at byte 2 of header described in rfc 1964, section 1.2.1: */
+        krb5_hdr = ptr - 2;
+        msg_start = krb5_hdr + 24;
+        /* XXXJBF: */ BUG_ON(buf->head[0].iov_base + offset + headlen != msg_start + blocksize);
+
+        *(u16 *)(krb5_hdr + 2) = htons(kctx->signalg);
+        memset(krb5_hdr + 4, 0xff, 4);
+        *(u16 *)(krb5_hdr + 4) = htons(kctx->sealalg);
+
+        make_confounder(msg_start, blocksize);
+
+        /* XXXJBF: UGH!: */
+        tmp_pages = buf->pages;
+        buf->pages = pages;
+        if (make_checksum(checksum_type, krb5_hdr, 8, buf,
+                                offset + headlen - blocksize, &md5cksum))
+                goto out_err;
+        buf->pages = tmp_pages;
+
+        switch (kctx->signalg) {
+        case SGN_ALG_DES_MAC_MD5:
+                if (krb5_encrypt(kctx->seq, NULL, md5cksum.data,
+                                  md5cksum.data, md5cksum.len))
+                        goto out_err;
+                memcpy(krb5_hdr + 16,
+                       md5cksum.data + md5cksum.len - KRB5_CKSUM_LENGTH,
+                       KRB5_CKSUM_LENGTH);
+
+                dprintk("RPC:      make_seal_token: cksum data: \n");
+                print_hexl((u32 *) (krb5_hdr + 16), KRB5_CKSUM_LENGTH, 0);
+                break;
+        default:
+                BUG();
+        }
+
+        kfree(md5cksum.data);
+
+        /* XXX would probably be more efficient to compute checksum
+         * and encrypt at the same time: */
+        if ((krb5_make_seq_num(kctx->seq, kctx->initiate ? 0 : 0xff,
+                               kctx->seq_send, krb5_hdr + 16, krb5_hdr + 8)))
+                goto out_err;
+
+        if (gss_encrypt_xdr_buf(kctx->enc, buf, offset + headlen - blocksize,
+                                                                        pages))
+                goto out_err;
+
+        kctx->seq_send++;
+
+        return ((kctx->endtime < now) ? GSS_S_CONTEXT_EXPIRED : GSS_S_COMPLETE);
+out_err:
+        if (md5cksum.data) kfree(md5cksum.data);
+        return GSS_S_FAILURE;
+}
+
+u32
+gss_unwrap_kerberos(struct gss_ctx *ctx, u32 *qop, int offset,
+                        struct xdr_buf *buf)
+{
+        struct krb5_ctx         *kctx = ctx->internal_ctx_id;
+        int                     signalg;
+        int                     sealalg;
+        s32                     checksum_type;
+        struct xdr_netobj       md5cksum = {.len = 0, .data = NULL};
+        s32                     now;
+        int                     direction;
+        s32                     seqnum;
+        unsigned char           *ptr;
+        int                     bodysize;
+        u32                     ret = GSS_S_DEFECTIVE_TOKEN;
+        void                    *data_start, *orig_start;
+        int                     data_len;
+        int                     blocksize;
+
+        dprintk("RPC:      gss_unwrap_kerberos\n");
+
+        ptr = (u8 *)buf->head[0].iov_base + offset;
+        if (g_verify_token_header(&kctx->mech_used, &bodysize, &ptr,
+                                        buf->len - offset))
+                goto out;
+
+        if ((*ptr++ != ((KG_TOK_WRAP_MSG>>8)&0xff)) ||
+            (*ptr++ !=  (KG_TOK_WRAP_MSG    &0xff))   )
+                goto out;
+
+        /* XXX sanity-check bodysize?? */
+
+        /* get the sign and seal algorithms */
+
+        signalg = ptr[0] + (ptr[1] << 8);
+        sealalg = ptr[2] + (ptr[3] << 8);
+
+        /* Sanity checks */
+
+        if ((ptr[4] != 0xff) || (ptr[5] != 0xff))
+                goto out;
+
+        if (sealalg == 0xffff)
+                goto out;
+
+        /* in the current spec, there is only one valid seal algorithm per
+           key type, so a simple comparison is ok */
+
+        if (sealalg != kctx->sealalg)
+                goto out;
+
+        /* there are several mappings of seal algorithms to sign algorithms,
+           but few enough that we can try them all. */
+
+        if ((kctx->sealalg == SEAL_ALG_NONE && signalg > 1) ||
+            (kctx->sealalg == SEAL_ALG_1 && signalg != SGN_ALG_3) ||
+            (kctx->sealalg == SEAL_ALG_DES3KD &&
+             signalg != SGN_ALG_HMAC_SHA1_DES3_KD))
+                goto out;
+
+        if (gss_decrypt_xdr_buf(kctx->enc, buf,
+                        ptr + 22 - (unsigned char *)buf->head[0].iov_base))
+                goto out;
+
+        /* compute the checksum of the message */
+
+        /* initialize the the cksum */
+        switch (signalg) {
+        case SGN_ALG_DES_MAC_MD5:
+                checksum_type = CKSUMTYPE_RSA_MD5;
+                break;
+        default:
+                ret = GSS_S_DEFECTIVE_TOKEN;
+                goto out;
+        }
+
+        switch (signalg) {
+        case SGN_ALG_DES_MAC_MD5:
+                ret = make_checksum(checksum_type, ptr - 2, 8, buf,
+                         ptr + 22 - (unsigned char *)buf->head[0].iov_base, &md5cksum);
+                if (ret)
+                        goto out;
+
+                ret = krb5_encrypt(kctx->seq, NULL, md5cksum.data,
+                                   md5cksum.data, md5cksum.len);
+                if (ret)
+                        goto out;
+
+                if (memcmp(md5cksum.data + 8, ptr + 14, 8)) {
+                        ret = GSS_S_BAD_SIG;
+                        goto out;
+                }
+                break;
+        default:
+                ret = GSS_S_DEFECTIVE_TOKEN;
+                goto out;
+        }
+
+        /* it got through unscathed.  Make sure the context is unexpired */
+
+        if (qop)
+                *qop = GSS_C_QOP_DEFAULT;
+
+        now = get_seconds();
+
+        ret = GSS_S_CONTEXT_EXPIRED;
+        if (now > kctx->endtime)
+                goto out;
+
+        /* do sequencing checks */
+
+        ret = GSS_S_BAD_SIG;
+        if ((ret = krb5_get_seq_num(kctx->seq, ptr + 14, ptr + 6, &direction,
+                                    &seqnum)))
+                goto out;
+
+        if ((kctx->initiate && direction != 0xff) ||
+            (!kctx->initiate && direction != 0))
+                goto out;
+
+        /* Copy the data back to the right position.  XXX: Would probably be
+         * better to copy and encrypt at the same time. */
+
+        blocksize = crypto_tfm_alg_blocksize(kctx->enc);
+        data_start = ptr + 22 + blocksize;
+        orig_start = buf->head[0].iov_base + offset;
+        data_len = (buf->head[0].iov_base + buf->head[0].iov_len) - data_start;
+        memmove(orig_start, data_start, data_len);
+        buf->head[0].iov_len -= (data_start - orig_start);
+        buf->len -= (data_start - orig_start);
+
+        ret = GSS_S_DEFECTIVE_TOKEN;
+        if (gss_krb5_remove_padding(buf, blocksize))
+                goto out;
+
+        ret = GSS_S_COMPLETE;
+out:
+        if (md5cksum.data) kfree(md5cksum.data);
+        return ret;
+}