// SPDX-License-Identifier: GPL-2.0-only
/*
 * ppp_deflate.c - interface the zlib procedures for Deflate compression
 * and decompression (as used by gzip) to the PPP code.
 *
 * Copyright 1994-1998 Paul Mackerras.
 */

#include <linux/module.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/init.h>
#include <linux/string.h>

#include <linux/ppp_defs.h>
#include <linux/ppp-comp.h>

#include <linux/zlib.h>
#include <asm/unaligned.h>

/*
 * State for a Deflate (de)compressor.
 */
struct ppp_deflate_state {
    int         seqno;
    int         w_size;
    int         unit;
    int         mru;
    int         debug;
    z_stream    strm;
    struct compstat stats;
};

#define DEFLATE_OVHD    2               /* Deflate overhead/packet */

static void     *z_comp_alloc(unsigned char *options, int opt_len);
static void     *z_decomp_alloc(unsigned char *options, int opt_len);
static void     z_comp_free(void *state);
static void     z_decomp_free(void *state);
static int      z_comp_init(void *state, unsigned char *options,
                                 int opt_len,
                                 int unit, int hdrlen, int debug);
static int      z_decomp_init(void *state, unsigned char *options,
                                   int opt_len,
                                   int unit, int hdrlen, int mru, int debug);
static int      z_compress(void *state, unsigned char *rptr,
                                unsigned char *obuf,
                                int isize, int osize);
static void     z_incomp(void *state, unsigned char *ibuf, int icnt);
static int      z_decompress(void *state, unsigned char *ibuf,
                                int isize, unsigned char *obuf, int osize);
static void     z_comp_reset(void *state);
static void     z_decomp_reset(void *state);
static void     z_comp_stats(void *state, struct compstat *stats);

/**
 *      z_comp_free - free the memory used by a compressor
 *      @arg:   pointer to the private state for the compressor.
 */
static void z_comp_free(void *arg)
{
        struct ppp_deflate_state *state = (struct ppp_deflate_state *) arg;

        if (state) {
                zlib_deflateEnd(&state->strm);
                vfree(state->strm.workspace);
                kfree(state);
        }
}

/**
 *      z_comp_alloc - allocate space for a compressor.
 *      @options: pointer to CCP option data
 *      @opt_len: length of the CCP option at @options.
 *
 *      The @options pointer points to the a buffer containing the
 *      CCP option data for the compression being negotiated.  It is
 *      formatted according to RFC1979, and describes the window
 *      size that the peer is requesting that we use in compressing
 *      data to be sent to it.
 *
 *      Returns the pointer to the private state for the compressor,
 *      or NULL if we could not allocate enough memory.
 */
static void *z_comp_alloc(unsigned char *options, int opt_len)
{
        struct ppp_deflate_state *state;
        int w_size;

        if (opt_len != CILEN_DEFLATE ||
            (options[0] != CI_DEFLATE && options[0] != CI_DEFLATE_DRAFT) ||
            options[1] != CILEN_DEFLATE ||
            DEFLATE_METHOD(options[2]) != DEFLATE_METHOD_VAL ||
            options[3] != DEFLATE_CHK_SEQUENCE)
                return NULL;
        w_size = DEFLATE_SIZE(options[2]);
        if (w_size < DEFLATE_MIN_SIZE || w_size > DEFLATE_MAX_SIZE)
                return NULL;

        state = kzalloc(sizeof(*state),
                                                     GFP_KERNEL);
        if (state == NULL)
                return NULL;

        state->strm.next_in   = NULL;
        state->w_size         = w_size;
        state->strm.workspace = vmalloc(zlib_deflate_workspacesize(-w_size, 8));
        if (state->strm.workspace == NULL)
                goto out_free;

        if (zlib_deflateInit2(&state->strm, Z_DEFAULT_COMPRESSION,
                         DEFLATE_METHOD_VAL, -w_size, 8, Z_DEFAULT_STRATEGY)
            != Z_OK)
                goto out_free;
        return (void *) state;

out_free:
        z_comp_free(state);
        return NULL;
}

/**
 *      z_comp_init - initialize a previously-allocated compressor.
 *      @arg:   pointer to the private state for the compressor
 *      @options: pointer to the CCP option data describing the
 *              compression that was negotiated with the peer
 *      @opt_len: length of the CCP option data at @options
 *      @unit:  PPP unit number for diagnostic messages
 *      @hdrlen: ignored (present for backwards compatibility)
 *      @debug: debug flag; if non-zero, debug messages are printed.
 *
 *      The CCP options described by @options must match the options
 *      specified when the compressor was allocated.  The compressor
 *      history is reset.  Returns 0 for failure (CCP options don't
 *      match) or 1 for success.
 */
static int z_comp_init(void *arg, unsigned char *options, int opt_len,
                       int unit, int hdrlen, int debug)
{
        struct ppp_deflate_state *state = (struct ppp_deflate_state *) arg;

        if (opt_len < CILEN_DEFLATE ||
            (options[0] != CI_DEFLATE && options[0] != CI_DEFLATE_DRAFT) ||
            options[1] != CILEN_DEFLATE ||
            DEFLATE_METHOD(options[2]) != DEFLATE_METHOD_VAL ||
            DEFLATE_SIZE(options[2]) != state->w_size ||
            options[3] != DEFLATE_CHK_SEQUENCE)
                return 0;

        state->seqno = 0;
        state->unit  = unit;
        state->debug = debug;

        zlib_deflateReset(&state->strm);

        return 1;
}

/**
 *      z_comp_reset - reset a previously-allocated compressor.
 *      @arg:   pointer to private state for the compressor.
 *
 *      This clears the history for the compressor and makes it
 *      ready to start emitting a new compressed stream.
 */
static void z_comp_reset(void *arg)
{
        struct ppp_deflate_state *state = (struct ppp_deflate_state *) arg;

        state->seqno = 0;
        zlib_deflateReset(&state->strm);
}

/**
 *      z_compress - compress a PPP packet with Deflate compression.
 *      @arg:   pointer to private state for the compressor
 *      @rptr:  uncompressed packet (input)
 *      @obuf:  compressed packet (output)
 *      @isize: size of uncompressed packet
 *      @osize: space available at @obuf
 *
 *      Returns the length of the compressed packet, or 0 if the
 *      packet is incompressible.
 */
static int z_compress(void *arg, unsigned char *rptr, unsigned char *obuf,
               int isize, int osize)
{
        struct ppp_deflate_state *state = (struct ppp_deflate_state *) arg;
        int r, proto, off, olen, oavail;
        unsigned char *wptr;

        /*
         * Check that the protocol is in the range we handle.
         */
        proto = PPP_PROTOCOL(rptr);
        if (proto > 0x3fff || proto == 0xfd || proto == 0xfb)
                return 0;

        /* Don't generate compressed packets which are larger than
           the uncompressed packet. */
        if (osize > isize)
                osize = isize;

        wptr = obuf;

        /*
         * Copy over the PPP header and store the 2-byte sequence number.
         */
        wptr[0] = PPP_ADDRESS(rptr);
        wptr[1] = PPP_CONTROL(rptr);
        put_unaligned_be16(PPP_COMP, wptr + 2);
        wptr += PPP_HDRLEN;
        put_unaligned_be16(state->seqno, wptr);
        wptr += DEFLATE_OVHD;
        olen = PPP_HDRLEN + DEFLATE_OVHD;
        state->strm.next_out = wptr;
        state->strm.avail_out = oavail = osize - olen;
        ++state->seqno;

        off = (proto > 0xff) ? 2 : 3;   /* skip 1st proto byte if 0 */
        rptr += off;
        state->strm.next_in = rptr;
        state->strm.avail_in = (isize - off);

        for (;;) {
                r = zlib_deflate(&state->strm, Z_PACKET_FLUSH);
                if (r != Z_OK) {
                        if (state->debug)
                                printk(KERN_ERR
                                       "z_compress: deflate returned %d\n", r);
                        break;
                }
                if (state->strm.avail_out == 0) {
                        olen += oavail;
                        state->strm.next_out = NULL;
                        state->strm.avail_out = oavail = 1000000;
                } else {
                        break;          /* all done */
                }
        }
        olen += oavail - state->strm.avail_out;

        /*
         * See if we managed to reduce the size of the packet.
         */
        if (olen < isize && olen <= osize) {
                state->stats.comp_bytes += olen;
                state->stats.comp_packets++;
        } else {
                state->stats.inc_bytes += isize;
                state->stats.inc_packets++;
                olen = 0;
        }
        state->stats.unc_bytes += isize;
        state->stats.unc_packets++;

        return olen;
}

/**
 *      z_comp_stats - return compression statistics for a compressor
 *              or decompressor.
 *      @arg:   pointer to private space for the (de)compressor
 *      @stats: pointer to a struct compstat to receive the result.
 */
static void z_comp_stats(void *arg, struct compstat *stats)
{
        struct ppp_deflate_state *state = (struct ppp_deflate_state *) arg;

        *stats = state->stats;
}

/**
 *      z_decomp_free - Free the memory used by a decompressor.
 *      @arg:   pointer to private space for the decompressor.
 */
static void z_decomp_free(void *arg)
{
        struct ppp_deflate_state *state = (struct ppp_deflate_state *) arg;

        if (state) {
                vfree(state->strm.workspace);
                kfree(state);
        }
}

/**
 *      z_decomp_alloc - allocate space for a decompressor.
 *      @options: pointer to CCP option data
 *      @opt_len: length of the CCP option at @options.
 *
 *      The @options pointer points to the a buffer containing the
 *      CCP option data for the compression being negotiated.  It is
 *      formatted according to RFC1979, and describes the window
 *      size that we are requesting the peer to use in compressing
 *      data to be sent to us.
 *
 *      Returns the pointer to the private state for the decompressor,
 *      or NULL if we could not allocate enough memory.
 */
static void *z_decomp_alloc(unsigned char *options, int opt_len)
{
        struct ppp_deflate_state *state;
        int w_size;

        if (opt_len != CILEN_DEFLATE ||
            (options[0] != CI_DEFLATE && options[0] != CI_DEFLATE_DRAFT) ||
            options[1] != CILEN_DEFLATE ||
            DEFLATE_METHOD(options[2]) != DEFLATE_METHOD_VAL ||
            options[3] != DEFLATE_CHK_SEQUENCE)
                return NULL;
        w_size = DEFLATE_SIZE(options[2]);
        if (w_size < DEFLATE_MIN_SIZE || w_size > DEFLATE_MAX_SIZE)
                return NULL;

        state = kzalloc(sizeof(*state), GFP_KERNEL);
        if (state == NULL)
                return NULL;

        state->w_size         = w_size;
        state->strm.next_out  = NULL;
        state->strm.workspace = vmalloc(zlib_inflate_workspacesize());
        if (state->strm.workspace == NULL)
                goto out_free;

        if (zlib_inflateInit2(&state->strm, -w_size) != Z_OK)
                goto out_free;
        return (void *) state;

out_free:
        z_decomp_free(state);
        return NULL;
}

/**
 *      z_decomp_init - initialize a previously-allocated decompressor.
 *      @arg:   pointer to the private state for the decompressor
 *      @options: pointer to the CCP option data describing the
 *              compression that was negotiated with the peer
 *      @opt_len: length of the CCP option data at @options
 *      @unit:  PPP unit number for diagnostic messages
 *      @hdrlen: ignored (present for backwards compatibility)
 *      @mru:   maximum length of decompressed packets
 *      @debug: debug flag; if non-zero, debug messages are printed.
 *
 *      The CCP options described by @options must match the options
 *      specified when the decompressor was allocated.  The decompressor
 *      history is reset.  Returns 0 for failure (CCP options don't
 *      match) or 1 for success.
 */
static int z_decomp_init(void *arg, unsigned char *options, int opt_len,
                         int unit, int hdrlen, int mru, int debug)
{
        struct ppp_deflate_state *state = (struct ppp_deflate_state *) arg;

        if (opt_len < CILEN_DEFLATE ||
            (options[0] != CI_DEFLATE && options[0] != CI_DEFLATE_DRAFT) ||
            options[1] != CILEN_DEFLATE ||
            DEFLATE_METHOD(options[2]) != DEFLATE_METHOD_VAL ||
            DEFLATE_SIZE(options[2]) != state->w_size ||
            options[3] != DEFLATE_CHK_SEQUENCE)
                return 0;

        state->seqno = 0;
        state->unit  = unit;
        state->debug = debug;
        state->mru   = mru;

        zlib_inflateReset(&state->strm);

        return 1;
}

/**
 *      z_decomp_reset - reset a previously-allocated decompressor.
 *      @arg:   pointer to private state for the decompressor.
 *
 *      This clears the history for the decompressor and makes it
 *      ready to receive a new compressed stream.
 */
static void z_decomp_reset(void *arg)
{
        struct ppp_deflate_state *state = (struct ppp_deflate_state *) arg;

        state->seqno = 0;
        zlib_inflateReset(&state->strm);
}

/**
 *      z_decompress - decompress a Deflate-compressed packet.
 *      @arg:   pointer to private state for the decompressor
 *      @ibuf:  pointer to input (compressed) packet data
 *      @isize: length of input packet
 *      @obuf:  pointer to space for output (decompressed) packet
 *      @osize: amount of space available at @obuf
 *
 * Because of patent problems, we return DECOMP_ERROR for errors
 * found by inspecting the input data and for system problems, but
 * DECOMP_FATALERROR for any errors which could possibly be said to
 * be being detected "after" decompression.  For DECOMP_ERROR,
 * we can issue a CCP reset-request; for DECOMP_FATALERROR, we may be
 * infringing a patent of Motorola's if we do, so we take CCP down
 * instead.
 *
 * Given that the frame has the correct sequence number and a good FCS,
 * errors such as invalid codes in the input most likely indicate a
 * bug, so we return DECOMP_FATALERROR for them in order to turn off
 * compression, even though they are detected by inspecting the input.
 */
static int z_decompress(void *arg, unsigned char *ibuf, int isize,
                 unsigned char *obuf, int osize)
{
        struct ppp_deflate_state *state = (struct ppp_deflate_state *) arg;
        int olen, seq, r;
        int decode_proto, overflow;
        unsigned char overflow_buf[1];

        if (isize <= PPP_HDRLEN + DEFLATE_OVHD) {
                if (state->debug)
                        printk(KERN_DEBUG "z_decompress%d: short pkt (%d)\n",
                               state->unit, isize);
                return DECOMP_ERROR;
        }

        /* Check the sequence number. */
        seq = get_unaligned_be16(ibuf + PPP_HDRLEN);
        if (seq != (state->seqno & 0xffff)) {
                if (state->debug)
                        printk(KERN_DEBUG "z_decompress%d: bad seq # %d, expected %d\n",
                               state->unit, seq, state->seqno & 0xffff);
                return DECOMP_ERROR;
        }
        ++state->seqno;

        /*
         * Fill in the first part of the PPP header.  The protocol field
         * comes from the decompressed data.
         */
        obuf[0] = PPP_ADDRESS(ibuf);
        obuf[1] = PPP_CONTROL(ibuf);
        obuf[2] = 0;

        /*
         * Set up to call inflate.  We set avail_out to 1 initially so we can
         * look at the first byte of the output and decide whether we have
         * a 1-byte or 2-byte protocol field.
         */
        state->strm.next_in = ibuf + PPP_HDRLEN + DEFLATE_OVHD;
        state->strm.avail_in = isize - (PPP_HDRLEN + DEFLATE_OVHD);
        state->strm.next_out = obuf + 3;
        state->strm.avail_out = 1;
        decode_proto = 1;
        overflow = 0;

        /*
         * Call inflate, supplying more input or output as needed.
         */
        for (;;) {
                r = zlib_inflate(&state->strm, Z_PACKET_FLUSH);
                if (r != Z_OK) {
                        if (state->debug)
                                printk(KERN_DEBUG "z_decompress%d: inflate returned %d (%s)\n",
                                       state->unit, r, (state->strm.msg? state->strm.msg: ""));
                        return DECOMP_FATALERROR;
                }
                if (state->strm.avail_out != 0)
                        break;          /* all done */
                if (decode_proto) {
                        state->strm.avail_out = osize - PPP_HDRLEN;
                        if ((obuf[3] & 1) == 0) {
                                /* 2-byte protocol field */
                                obuf[2] = obuf[3];
                                --state->strm.next_out;
                                ++state->strm.avail_out;
                        }
                        decode_proto = 0;
                } else if (!overflow) {
                        /*
                         * We've filled up the output buffer; the only way to
                         * find out whether inflate has any more characters
                         * left is to give it another byte of output space.
                         */
                        state->strm.next_out = overflow_buf;
                        state->strm.avail_out = 1;
                        overflow = 1;
                } else {
                        if (state->debug)
                                printk(KERN_DEBUG "z_decompress%d: ran out of mru\n",
                                       state->unit);
                        return DECOMP_FATALERROR;
                }
        }

        if (decode_proto) {
                if (state->debug)
                        printk(KERN_DEBUG "z_decompress%d: didn't get proto\n",
                               state->unit);
                return DECOMP_ERROR;
        }

        olen = osize + overflow - state->strm.avail_out;
        state->stats.unc_bytes += olen;
        state->stats.unc_packets++;
        state->stats.comp_bytes += isize;
        state->stats.comp_packets++;

        return olen;
}

/**
 *      z_incomp - add incompressible input data to the history.
 *      @arg:   pointer to private state for the decompressor
 *      @ibuf:  pointer to input packet data
 *      @icnt:  length of input data.
 */
static void z_incomp(void *arg, unsigned char *ibuf, int icnt)
{
        struct ppp_deflate_state *state = (struct ppp_deflate_state *) arg;
        int proto, r;

        /*
         * Check that the protocol is one we handle.
         */
        proto = PPP_PROTOCOL(ibuf);
        if (proto > 0x3fff || proto == 0xfd || proto == 0xfb)
                return;

        ++state->seqno;

        /*
         * We start at the either the 1st or 2nd byte of the protocol field,
         * depending on whether the protocol value is compressible.
         */
        state->strm.next_in = ibuf + 3;
        state->strm.avail_in = icnt - 3;
        if (proto > 0xff) {
                --state->strm.next_in;
                ++state->strm.avail_in;
        }

        r = zlib_inflateIncomp(&state->strm);
        if (r != Z_OK) {
                /* gak! */
                if (state->debug) {
                        printk(KERN_DEBUG "z_incomp%d: inflateIncomp returned %d (%s)\n",
                               state->unit, r, (state->strm.msg? state->strm.msg: ""));
                }
                return;
        }

        /*
         * Update stats.
         */
        state->stats.inc_bytes += icnt;
        state->stats.inc_packets++;
        state->stats.unc_bytes += icnt;
        state->stats.unc_packets++;
}

/*************************************************************
 * Module interface table
 *************************************************************/

/* These are in ppp_generic.c */
extern int  ppp_register_compressor   (struct compressor *cp);
extern void ppp_unregister_compressor (struct compressor *cp);

/*
 * Procedures exported to if_ppp.c.
 */
static struct compressor ppp_deflate = {
        .compress_proto =       CI_DEFLATE,
        .comp_alloc =           z_comp_alloc,
        .comp_free =            z_comp_free,
        .comp_init =            z_comp_init,
        .comp_reset =           z_comp_reset,
        .compress =             z_compress,
        .comp_stat =            z_comp_stats,
        .decomp_alloc =         z_decomp_alloc,
        .decomp_free =          z_decomp_free,
        .decomp_init =          z_decomp_init,
        .decomp_reset =         z_decomp_reset,
        .decompress =           z_decompress,
        .incomp =               z_incomp,
        .decomp_stat =          z_comp_stats,
        .owner =                THIS_MODULE
};

static struct compressor ppp_deflate_draft = {
        .compress_proto =       CI_DEFLATE_DRAFT,
        .comp_alloc =           z_comp_alloc,
        .comp_free =            z_comp_free,
        .comp_init =            z_comp_init,
        .comp_reset =           z_comp_reset,
        .compress =             z_compress,
        .comp_stat =            z_comp_stats,
        .decomp_alloc =         z_decomp_alloc,
        .decomp_free =          z_decomp_free,
        .decomp_init =          z_decomp_init,
        .decomp_reset =         z_decomp_reset,
        .decompress =           z_decompress,
        .incomp =               z_incomp,
        .decomp_stat =          z_comp_stats,
        .owner =                THIS_MODULE
};

static int __init deflate_init(void)
{
        int rc;

        rc = ppp_register_compressor(&ppp_deflate);
        if (rc)
                return rc;

        rc = ppp_register_compressor(&ppp_deflate_draft);
        if (rc) {
                ppp_unregister_compressor(&ppp_deflate);
                return rc;
        }

        pr_info("PPP Deflate Compression module registered\n");
        return 0;
}

static void __exit deflate_cleanup(void)
{
        ppp_unregister_compressor(&ppp_deflate);
        ppp_unregister_compressor(&ppp_deflate_draft);
}

module_init(deflate_init);
module_exit(deflate_cleanup);
MODULE_LICENSE("Dual BSD/GPL");
MODULE_ALIAS("ppp-compress-" __stringify(CI_DEFLATE));
MODULE_ALIAS("ppp-compress-" __stringify(CI_DEFLATE_DRAFT));