/*
 * Copyright (C) 2003 Christophe Saout <christophe@saout.de>
 *
 * This file is released under the GPL.
 */

#include <linux/module.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/bio.h>
#include <linux/blkdev.h>
#include <linux/mempool.h>
#include <linux/slab.h>
#include <linux/crypto.h>
#include <linux/workqueue.h>
#include <asm/atomic.h>
#include <asm/scatterlist.h>

#include "dm.h"

#define PFX     "crypt: "

/*
 * per bio private data
 */
struct crypt_io {
        struct dm_target *target;
        struct bio *bio;
        struct bio *first_clone;
        struct work_struct work;
        atomic_t pending;
        int error;
};

/*
 * context holding the current state of a multi-part conversion
 */
struct convert_context {
        struct bio *bio_in;
        struct bio *bio_out;
        unsigned int offset_in;
        unsigned int offset_out;
        int idx_in;
        int idx_out;
        sector_t sector;
        int write;
};

/*
 * Crypt: maps a linear range of a block device
 * and encrypts / decrypts at the same time.
 */
struct crypt_config {
        struct dm_dev *dev;
        sector_t start;

        /*
         * pool for per bio private data and
         * for encryption buffer pages
         */
        mempool_t *io_pool;
        mempool_t *page_pool;

        /*
         * crypto related data
         */
        struct crypto_tfm *tfm;
        sector_t iv_offset;
        int (*iv_generator)(struct crypt_config *cc, u8 *iv, sector_t sector);
        int iv_size;
        int key_size;
        u8 key[0];
};

#define MIN_IOS        256
#define MIN_POOL_PAGES 32
#define MIN_BIO_PAGES  8

static kmem_cache_t *_crypt_io_pool;

/*
 * Mempool alloc and free functions for the page
 */
static void *mempool_alloc_page(int gfp_mask, void *data)
{
        return alloc_page(gfp_mask);
}

static void mempool_free_page(void *page, void *data)
{
        __free_page(page);
}


/*
 * Different IV generation algorithms
 */
static int crypt_iv_plain(struct crypt_config *cc, u8 *iv, sector_t sector)
{
        *(u32 *)iv = cpu_to_le32(sector & 0xffffffff);
        if (cc->iv_size > sizeof(u32) / sizeof(u8))
                memset(iv + (sizeof(u32) / sizeof(u8)), 0,
                       cc->iv_size - (sizeof(u32) / sizeof(u8)));

        return 0;
}

static inline int
crypt_convert_scatterlist(struct crypt_config *cc, struct scatterlist *out,
                          struct scatterlist *in, unsigned int length,
                          int write, sector_t sector)
{
        u8 iv[cc->iv_size];
        int r;

        if (cc->iv_generator) {
                r = cc->iv_generator(cc, iv, sector);
                if (r < 0)
                        return r;

                if (write)
                        r = crypto_cipher_encrypt_iv(cc->tfm, out, in, length, iv);
                else
                        r = crypto_cipher_decrypt_iv(cc->tfm, out, in, length, iv);
        } else {
                if (write)
                        r = crypto_cipher_encrypt(cc->tfm, out, in, length);
                else
                        r = crypto_cipher_decrypt(cc->tfm, out, in, length);
        }

        return r;
}

static void
crypt_convert_init(struct crypt_config *cc, struct convert_context *ctx,
                   struct bio *bio_out, struct bio *bio_in,
                   sector_t sector, int write)
{
        ctx->bio_in = bio_in;
        ctx->bio_out = bio_out;
        ctx->offset_in = 0;
        ctx->offset_out = 0;
        ctx->idx_in = bio_in ? bio_in->bi_idx : 0;
        ctx->idx_out = bio_out ? bio_out->bi_idx : 0;
        ctx->sector = sector + cc->iv_offset;
        ctx->write = write;
}

/*
 * Encrypt / decrypt data from one bio to another one (can be the same one)
 */
static int crypt_convert(struct crypt_config *cc,
                         struct convert_context *ctx)
{
        int r = 0;

        while(ctx->idx_in < ctx->bio_in->bi_vcnt &&
              ctx->idx_out < ctx->bio_out->bi_vcnt) {
                struct bio_vec *bv_in = bio_iovec_idx(ctx->bio_in, ctx->idx_in);
                struct bio_vec *bv_out = bio_iovec_idx(ctx->bio_out, ctx->idx_out);
                struct scatterlist sg_in = {
                        .page = bv_in->bv_page,
                        .offset = bv_in->bv_offset + ctx->offset_in,
                        .length = 1 << SECTOR_SHIFT
                };
                struct scatterlist sg_out = {
                        .page = bv_out->bv_page,
                        .offset = bv_out->bv_offset + ctx->offset_out,
                        .length = 1 << SECTOR_SHIFT
                };

                ctx->offset_in += sg_in.length;
                if (ctx->offset_in >= bv_in->bv_len) {
                        ctx->offset_in = 0;
                        ctx->idx_in++;
                }

                ctx->offset_out += sg_out.length;
                if (ctx->offset_out >= bv_out->bv_len) {
                        ctx->offset_out = 0;
                        ctx->idx_out++;
                }

                r = crypt_convert_scatterlist(cc, &sg_out, &sg_in, sg_in.length,
                                              ctx->write, ctx->sector);
                if (r < 0)
                        break;

                ctx->sector++;
        }

        return r;
}

/*
 * Generate a new unfragmented bio with the given size
 * This should never violate the device limitations
 * May return a smaller bio when running out of pages
 */
static struct bio *
crypt_alloc_buffer(struct crypt_config *cc, unsigned int size,
                   struct bio *base_bio, int *bio_vec_idx)
{
        struct bio *bio;
        int nr_iovecs = dm_div_up(size, PAGE_SIZE);
        int gfp_mask = GFP_NOIO | __GFP_HIGHMEM;
        int flags = current->flags;
        int i;

        /*
         * Tell VM to act less aggressively and fail earlier.
         * This is not necessary but increases throughput.
         * FIXME: Is this really intelligent?
         */
        current->flags &= ~PF_MEMALLOC;

        if (base_bio)
                bio = bio_clone(base_bio, GFP_NOIO);
        else
                bio = bio_alloc(GFP_NOIO, nr_iovecs);
        if (!bio) {
                if (flags & PF_MEMALLOC)
                        current->flags |= PF_MEMALLOC;
                return NULL;
        }

        /* if the last bio was not complete, continue where that one ended */
        bio->bi_idx = *bio_vec_idx;
        bio->bi_vcnt = *bio_vec_idx;
        bio->bi_size = 0;
        bio->bi_flags &= ~(1 << BIO_SEG_VALID);

        /* bio->bi_idx pages have already been allocated */
        size -= bio->bi_idx * PAGE_SIZE;

        for(i = bio->bi_idx; i < nr_iovecs; i++) {
                struct bio_vec *bv = bio_iovec_idx(bio, i);

                bv->bv_page = mempool_alloc(cc->page_pool, gfp_mask);
                if (!bv->bv_page)
                        break;

                /*
                 * if additional pages cannot be allocated without waiting,
                 * return a partially allocated bio, the caller will then try
                 * to allocate additional bios while submitting this partial bio
                 */
                if ((i - bio->bi_idx) == (MIN_BIO_PAGES - 1))
                        gfp_mask = (gfp_mask | __GFP_NOWARN) & ~__GFP_WAIT;

                bv->bv_offset = 0;
                if (size > PAGE_SIZE)
                        bv->bv_len = PAGE_SIZE;
                else
                        bv->bv_len = size;

                bio->bi_size += bv->bv_len;
                bio->bi_vcnt++;
                size -= bv->bv_len;
        }

        if (flags & PF_MEMALLOC)
                current->flags |= PF_MEMALLOC;

        if (!bio->bi_size) {
                bio_put(bio);
                return NULL;
        }

        /*
         * Remember the last bio_vec allocated to be able
         * to correctly continue after the splitting.
         */
        *bio_vec_idx = bio->bi_vcnt;

        return bio;
}

static void crypt_free_buffer_pages(struct crypt_config *cc,
                                    struct bio *bio, unsigned int bytes)
{
        unsigned int start, end;
        struct bio_vec *bv;
        int i;

        /*
         * This is ugly, but Jens Axboe thinks that using bi_idx in the
         * endio function is too dangerous at the moment, so I calculate the
         * correct position using bi_vcnt and bi_size.
         * The bv_offset and bv_len fields might already be modified but we
         * know that we always allocated whole pages.
         * A fix to the bi_idx issue in the kernel is in the works, so
         * we will hopefully be able to revert to the cleaner solution soon.
         */
        i = bio->bi_vcnt - 1;
        bv = bio_iovec_idx(bio, i);
        end = (i << PAGE_SHIFT) + (bv->bv_offset + bv->bv_len) - bio->bi_size;
        start = end - bytes;

        start >>= PAGE_SHIFT;
        if (!bio->bi_size)
                end = bio->bi_vcnt;
        else
                end >>= PAGE_SHIFT;

        for(i = start; i < end; i++) {
                bv = bio_iovec_idx(bio, i);
                BUG_ON(!bv->bv_page);
                mempool_free(bv->bv_page, cc->page_pool);
                bv->bv_page = NULL;
        }
}

/*
 * One of the bios was finished. Check for completion of
 * the whole request and correctly clean up the buffer.
 */
static void dec_pending(struct crypt_io *io, int error)
{
        struct crypt_config *cc = (struct crypt_config *) io->target->private;

        if (error < 0)
                io->error = error;

        if (!atomic_dec_and_test(&io->pending))
                return;

        if (io->first_clone)
                bio_put(io->first_clone);

        bio_endio(io->bio, io->bio->bi_size, io->error);

        mempool_free(io, cc->io_pool);
}

/*
 * kcryptd:
 *
 * Needed because it would be very unwise to do decryption in an
 * interrupt context, so bios returning from read requests get
 * queued here.
 */
static struct workqueue_struct *_kcryptd_workqueue;

static void kcryptd_do_work(void *data)
{
        struct crypt_io *io = (struct crypt_io *) data;
        struct crypt_config *cc = (struct crypt_config *) io->target->private;
        struct convert_context ctx;
        int r;

        crypt_convert_init(cc, &ctx, io->bio, io->bio,
                           io->bio->bi_sector - io->target->begin, 0);
        r = crypt_convert(cc, &ctx);

        dec_pending(io, r);
}

static void kcryptd_queue_io(struct crypt_io *io)
{
        INIT_WORK(&io->work, kcryptd_do_work, io);
        queue_work(_kcryptd_workqueue, &io->work);
}

/*
 * Decode key from its hex representation
 */
static int crypt_decode_key(u8 *key, char *hex, int size)
{
        char buffer[3];
        char *endp;
        int i;

        buffer[2] = '\0';

        for(i = 0; i < size; i++) {
                buffer[0] = *hex++;
                buffer[1] = *hex++;

                key[i] = (u8)simple_strtoul(buffer, &endp, 16);

                if (endp != &buffer[2])
                        return -EINVAL;
        }

        if (*hex != '\0')
                return -EINVAL;

        return 0;
}

/*
 * Encode key into its hex representation
 */
static void crypt_encode_key(char *hex, u8 *key, int size)
{
        int i;

        for(i = 0; i < size; i++) {
                sprintf(hex, "%02x", *key);
                hex += 2;
                key++;
        }
}

/*
 * Construct an encryption mapping:
 * <cipher> <key> <iv_offset> <dev_path> <start>
 */
static int crypt_ctr(struct dm_target *ti, unsigned int argc, char **argv)
{
        struct crypt_config *cc;
        struct crypto_tfm *tfm;
        char *tmp;
        char *cipher;
        char *mode;
        int crypto_flags;
        int key_size;

        if (argc != 5) {
                ti->error = PFX "Not enough arguments";
                return -EINVAL;
        }

        tmp = argv[0];
        cipher = strsep(&tmp, "-");
        mode = strsep(&tmp, "-");

        if (tmp)
                DMWARN(PFX "Unexpected additional cipher options");

        key_size = strlen(argv[1]) >> 1;

        cc = kmalloc(sizeof(*cc) + key_size * sizeof(u8), GFP_KERNEL);
        if (cc == NULL) {
                ti->error =
                        PFX "Cannot allocate transparent encryption context";
                return -ENOMEM;
        }

        if (!mode || strcmp(mode, "plain") == 0)
                cc->iv_generator = crypt_iv_plain;
        else if (strcmp(mode, "ecb") == 0)
                cc->iv_generator = NULL;
        else {
                ti->error = PFX "Invalid chaining mode";
                goto bad1;
        }

        if (cc->iv_generator)
                crypto_flags = CRYPTO_TFM_MODE_CBC;
        else
                crypto_flags = CRYPTO_TFM_MODE_ECB;

        tfm = crypto_alloc_tfm(cipher, crypto_flags);
        if (!tfm) {
                ti->error = PFX "Error allocating crypto tfm";
                goto bad1;
        }
        if (crypto_tfm_alg_type(tfm) != CRYPTO_ALG_TYPE_CIPHER) {
                ti->error = PFX "Expected cipher algorithm";
                goto bad2;
        }

        if (tfm->crt_cipher.cit_decrypt_iv && tfm->crt_cipher.cit_encrypt_iv)
                /* at least a 32 bit sector number should fit in our buffer */
                cc->iv_size = max(crypto_tfm_alg_ivsize(tfm),
                                  (unsigned int)(sizeof(u32) / sizeof(u8)));
        else {
                cc->iv_size = 0;
                if (cc->iv_generator) {
                        DMWARN(PFX "Selected cipher does not support IVs");
                        cc->iv_generator = NULL;
                }
        }

        cc->io_pool = mempool_create(MIN_IOS, mempool_alloc_slab,
                                     mempool_free_slab, _crypt_io_pool);
        if (!cc->io_pool) {
                ti->error = PFX "Cannot allocate crypt io mempool";
                goto bad2;
        }

        cc->page_pool = mempool_create(MIN_POOL_PAGES, mempool_alloc_page,
                                       mempool_free_page, NULL);
        if (!cc->page_pool) {
                ti->error = PFX "Cannot allocate page mempool";
                goto bad3;
        }

        cc->tfm = tfm;
        cc->key_size = key_size;
        if ((key_size == 0 && strcmp(argv[1], "-") != 0)
            || crypt_decode_key(cc->key, argv[1], key_size) < 0) {
                ti->error = PFX "Error decoding key";
                goto bad4;
        }

        if (tfm->crt_cipher.cit_setkey(tfm, cc->key, key_size) < 0) {
                ti->error = PFX "Error setting key";
                goto bad4;
        }

        if (sscanf(argv[2], SECTOR_FORMAT, &cc->iv_offset) != 1) {
                ti->error = PFX "Invalid iv_offset sector";
                goto bad4;
        }

        if (sscanf(argv[4], SECTOR_FORMAT, &cc->start) != 1) {
                ti->error = PFX "Invalid device sector";
                goto bad4;
        }

        if (dm_get_device(ti, argv[3], cc->start, ti->len,
                          dm_table_get_mode(ti->table), &cc->dev)) {
                ti->error = PFX "Device lookup failed";
                goto bad4;
        }

        ti->private = cc;
        return 0;

bad4:
        mempool_destroy(cc->page_pool);
bad3:
        mempool_destroy(cc->io_pool);
bad2:
        crypto_free_tfm(tfm);
bad1:
        kfree(cc);
        return -EINVAL;
}

static void crypt_dtr(struct dm_target *ti)
{
        struct crypt_config *cc = (struct crypt_config *) ti->private;

        mempool_destroy(cc->page_pool);
        mempool_destroy(cc->io_pool);

        crypto_free_tfm(cc->tfm);
        dm_put_device(ti, cc->dev);
        kfree(cc);
}

static int crypt_endio(struct bio *bio, unsigned int done, int error)
{
        struct crypt_io *io = (struct crypt_io *) bio->bi_private;
        struct crypt_config *cc = (struct crypt_config *) io->target->private;

        if (bio_data_dir(bio) == WRITE) {
                /*
                 * free the processed pages, even if
                 * it's only a partially completed write
                 */
                crypt_free_buffer_pages(cc, bio, done);
        }

        if (bio->bi_size)
                return 1;

        bio_put(bio);

        /*
         * successful reads are decrypted by the worker thread
         */
        if ((bio_data_dir(bio) == READ)
            && bio_flagged(bio, BIO_UPTODATE)) {
                kcryptd_queue_io(io);
                return 0;
        }

        dec_pending(io, error);
        return error;
}

static inline struct bio *
crypt_clone(struct crypt_config *cc, struct crypt_io *io, struct bio *bio,
            sector_t sector, int *bvec_idx, struct convert_context *ctx)
{
        struct bio *clone;

        if (bio_data_dir(bio) == WRITE) {
                clone = crypt_alloc_buffer(cc, bio->bi_size,
                                 io->first_clone, bvec_idx);
                if (clone) {
                        ctx->bio_out = clone;
                        if (crypt_convert(cc, ctx) < 0) {
                                crypt_free_buffer_pages(cc, clone,
                                                        clone->bi_size);
                                bio_put(clone);
                                return NULL;
                        }
                }
        } else {
                /*
                 * The block layer might modify the bvec array, so always
                 * copy the required bvecs because we need the original
                 * one in order to decrypt the whole bio data *afterwards*.
                 */
                clone = bio_alloc(GFP_NOIO, bio_segments(bio));
                if (clone) {
                        clone->bi_idx = 0;
                        clone->bi_vcnt = bio_segments(bio);
                        clone->bi_size = bio->bi_size;
                        memcpy(clone->bi_io_vec, bio_iovec(bio),
                               sizeof(struct bio_vec) * clone->bi_vcnt);
                }
        }

        if (!clone)
                return NULL;

        clone->bi_private = io;
        clone->bi_end_io = crypt_endio;
        clone->bi_bdev = cc->dev->bdev;
        clone->bi_sector = cc->start + sector;
        clone->bi_rw = bio->bi_rw;

        return clone;
}

static int crypt_map(struct dm_target *ti, struct bio *bio,
                     union map_info *map_context)
{
        struct crypt_config *cc = (struct crypt_config *) ti->private;
        struct crypt_io *io = mempool_alloc(cc->io_pool, GFP_NOIO);
        struct convert_context ctx;
        struct bio *clone;
        unsigned int remaining = bio->bi_size;
        sector_t sector = bio->bi_sector - ti->begin;
        int bvec_idx = 0;

        io->target = ti;
        io->bio = bio;
        io->first_clone = NULL;
        io->error = 0;
        atomic_set(&io->pending, 1); /* hold a reference */

        if (bio_data_dir(bio) == WRITE)
                crypt_convert_init(cc, &ctx, NULL, bio, sector, 1);

        /*
         * The allocated buffers can be smaller than the whole bio,
         * so repeat the whole process until all the data can be handled.
         */
        while (remaining) {
                clone = crypt_clone(cc, io, bio, sector, &bvec_idx, &ctx);
                if (!clone)
                        goto cleanup;

                if (!io->first_clone) {
                        /*
                         * hold a reference to the first clone, because it
                         * holds the bio_vec array and that can't be freed
                         * before all other clones are released
                         */
                        bio_get(clone);
                        io->first_clone = clone;
                }
                atomic_inc(&io->pending);

                remaining -= clone->bi_size;
                sector += bio_sectors(clone);

                generic_make_request(clone);

                /* out of memory -> run queues */
                if (remaining)
                        blk_congestion_wait(bio_data_dir(clone), HZ/100);
        }

        /* drop reference, clones could have returned before we reach this */
        dec_pending(io, 0);
        return 0;

cleanup:
        if (io->first_clone) {
                dec_pending(io, -ENOMEM);
                return 0;
        }

        /* if no bio has been dispatched yet, we can directly return the error */
        mempool_free(io, cc->io_pool);
        return -ENOMEM;
}

static int crypt_status(struct dm_target *ti, status_type_t type,
                        char *result, unsigned int maxlen)
{
        struct crypt_config *cc = (struct crypt_config *) ti->private;
        char buffer[32];
        const char *cipher;
        const char *mode = NULL;
        int offset;

        switch (type) {
        case STATUSTYPE_INFO:
                result[0] = '\0';
                break;

        case STATUSTYPE_TABLE:
                cipher = crypto_tfm_alg_name(cc->tfm);

                switch(cc->tfm->crt_cipher.cit_mode) {
                case CRYPTO_TFM_MODE_CBC:
                        mode = "plain";
                        break;
                case CRYPTO_TFM_MODE_ECB:
                        mode = "ecb";
                        break;
                default:
                        BUG();
                }

                snprintf(result, maxlen, "%s-%s ", cipher, mode);
                offset = strlen(result);

                if (cc->key_size > 0) {
                        if ((maxlen - offset) < ((cc->key_size << 1) + 1))
                                return -ENOMEM;

                        crypt_encode_key(result + offset, cc->key, cc->key_size);
                        offset += cc->key_size << 1;
                } else {
                        if (offset >= maxlen)
                                return -ENOMEM;
                        result[offset++] = '-';
                }

                format_dev_t(buffer, cc->dev->bdev->bd_dev);
                snprintf(result + offset, maxlen - offset, " " SECTOR_FORMAT
                         " %s " SECTOR_FORMAT, cc->iv_offset,
                         buffer, cc->start);
                break;
        }
        return 0;
}

static struct target_type crypt_target = {
        .name   = "crypt",
        .version= {1, 0, 0},
        .module = THIS_MODULE,
        .ctr    = crypt_ctr,
        .dtr    = crypt_dtr,
        .map    = crypt_map,
        .status = crypt_status,
};

static int __init dm_crypt_init(void)
{
        int r;

        _crypt_io_pool = kmem_cache_create("dm-crypt_io",
                                           sizeof(struct crypt_io),
                                           0, 0, NULL, NULL);
        if (!_crypt_io_pool)
                return -ENOMEM;

        _kcryptd_workqueue = create_workqueue("kcryptd");
        if (!_kcryptd_workqueue) {
                r = -ENOMEM;
                DMERR(PFX "couldn't create kcryptd");
                goto bad1;
        }

        r = dm_register_target(&crypt_target);
        if (r < 0) {
                DMERR(PFX "register failed %d", r);
                goto bad2;
        }

        return 0;

bad2:
        destroy_workqueue(_kcryptd_workqueue);
bad1:
        kmem_cache_destroy(_crypt_io_pool);
        return r;
}

static void __exit dm_crypt_exit(void)
{
        int r = dm_unregister_target(&crypt_target);

        if (r < 0)
                DMERR(PFX "unregister failed %d", r);

        destroy_workqueue(_kcryptd_workqueue);
        kmem_cache_destroy(_crypt_io_pool);
}

module_init(dm_crypt_init);
module_exit(dm_crypt_exit);

MODULE_AUTHOR("Christophe Saout <christophe@saout.de>");
MODULE_DESCRIPTION(DM_NAME " target for transparent encryption / decryption");
MODULE_LICENSE("GPL");