/*-
 * SPDX-License-Identifier: BSD-2-Clause
 *
 * Copyright 2003-2005 Colin Percival
 * All rights reserved
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted providing that the following conditions 
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
 * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

#include <sys/cdefs.h>
#ifndef WITHOUT_CAPSICUM
#include <sys/capsicum.h>
#endif

#include <bzlib.h>
#include <err.h>
#include <fcntl.h>
#include <libgen.h>
#include <limits.h>
#include <stdckdint.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/mman.h>

#ifndef O_BINARY
#define O_BINARY 0
#endif
#define HEADER_SIZE 32

static char *newfile;
static int dirfd = -1;

static void
exit_cleanup(void)
{

        if (dirfd != -1 && newfile != NULL)
                if (unlinkat(dirfd, newfile, 0))
                        warn("unlinkat");
}

static inline off_t
add_off_t(off_t a, off_t b)
{
        off_t result;

        if (ckd_add(&result, a, b))
                errx(1, "Corrupt patch");
        return result;
}

static off_t offtin(u_char *buf)
{
        off_t y;

        y = buf[7] & 0x7F;
        y = y * 256; y += buf[6];
        y = y * 256; y += buf[5];
        y = y * 256; y += buf[4];
        y = y * 256; y += buf[3];
        y = y * 256; y += buf[2];
        y = y * 256; y += buf[1];
        y = y * 256; y += buf[0];

        if (buf[7] & 0x80)
                y = -y;

        return (y);
}

static void
usage(void)
{

        fprintf(stderr, "usage: bspatch oldfile newfile patchfile\n");
        exit(1);
}

int main(int argc, char *argv[])
{
        FILE *f, *cpf, *dpf, *epf;
        BZFILE *cpfbz2, *dpfbz2, *epfbz2;
        char *directory, *namebuf;
        int cbz2err, dbz2err, ebz2err;
        int newfd, oldfd;
        off_t oldsize, newsize;
        off_t bzctrllen, bzdatalen;
        u_char header[HEADER_SIZE], buf[8];
        u_char *old, *new;
        off_t oldpos, newpos;
        off_t ctrl[3];
        off_t i, lenread, offset;
#ifndef WITHOUT_CAPSICUM
        cap_rights_t rights_dir, rights_ro, rights_wr;
#endif

        if (argc != 4)
                usage();

        /* Open patch file */
        if ((f = fopen(argv[3], "rb")) == NULL)
                err(1, "fopen(%s)", argv[3]);
        /* Open patch file for control block */
        if ((cpf = fopen(argv[3], "rb")) == NULL)
                err(1, "fopen(%s)", argv[3]);
        /* open patch file for diff block */
        if ((dpf = fopen(argv[3], "rb")) == NULL)
                err(1, "fopen(%s)", argv[3]);
        /* open patch file for extra block */
        if ((epf = fopen(argv[3], "rb")) == NULL)
                err(1, "fopen(%s)", argv[3]);
        /* open oldfile */
        if ((oldfd = open(argv[1], O_RDONLY | O_BINARY, 0)) < 0)
                err(1, "open(%s)", argv[1]);
        /* open directory where we'll write newfile */
        if ((namebuf = strdup(argv[2])) == NULL ||
            (directory = dirname(namebuf)) == NULL ||
            (dirfd = open(directory, O_DIRECTORY)) < 0)
                err(1, "open %s", argv[2]);
        free(namebuf);
        if ((newfile = basename(argv[2])) == NULL)
                err(1, "basename");
        /* open newfile */
        if ((newfd = openat(dirfd, newfile,
            O_CREAT | O_TRUNC | O_WRONLY | O_BINARY, 0666)) < 0)
                err(1, "open(%s)", argv[2]);
        atexit(exit_cleanup);

#ifndef WITHOUT_CAPSICUM
        if (cap_enter() < 0)
                err(1, "failed to enter security sandbox");

        cap_rights_init(&rights_ro, CAP_READ, CAP_FSTAT, CAP_SEEK, CAP_MMAP_R);
        cap_rights_init(&rights_wr, CAP_WRITE);
        cap_rights_init(&rights_dir, CAP_UNLINKAT);

        if (cap_rights_limit(fileno(f), &rights_ro) < 0 ||
            cap_rights_limit(fileno(cpf), &rights_ro) < 0 ||
            cap_rights_limit(fileno(dpf), &rights_ro) < 0 ||
            cap_rights_limit(fileno(epf), &rights_ro) < 0 ||
            cap_rights_limit(oldfd, &rights_ro) < 0 ||
            cap_rights_limit(newfd, &rights_wr) < 0 ||
            cap_rights_limit(dirfd, &rights_dir) < 0)
                err(1, "cap_rights_limit() failed, could not restrict"
                    " capabilities");
#endif

        /*
        File format:
                0       8       "BSDIFF40"
                8       8       X
                16      8       Y
                24      8       sizeof(newfile)
                32      X       bzip2(control block)
                32+X    Y       bzip2(diff block)
                32+X+Y  ???     bzip2(extra block)
        with control block a set of triples (x,y,z) meaning "add x bytes
        from oldfile to x bytes from the diff block; copy y bytes from the
        extra block; seek forwards in oldfile by z bytes".
        */

        /* Read header */
        if (fread(header, 1, HEADER_SIZE, f) < HEADER_SIZE) {
                if (feof(f))
                        errx(1, "Corrupt patch");
                err(1, "fread(%s)", argv[3]);
        }

        /* Check for appropriate magic */
        if (memcmp(header, "BSDIFF40", 8) != 0)
                errx(1, "Corrupt patch");

        /* Read lengths from header */
        bzctrllen = offtin(header + 8);
        bzdatalen = offtin(header + 16);
        newsize = offtin(header + 24);
        if (bzctrllen < 0 || bzctrllen > OFF_MAX - HEADER_SIZE ||
            bzdatalen < 0 || bzctrllen + HEADER_SIZE > OFF_MAX - bzdatalen ||
            newsize < 0 || newsize > SSIZE_MAX)
                errx(1, "Corrupt patch");

        /* Close patch file and re-open it via libbzip2 at the right places */
        if (fclose(f))
                err(1, "fclose(%s)", argv[3]);
        offset = HEADER_SIZE;
        if (fseeko(cpf, offset, SEEK_SET))
                err(1, "fseeko(%s, %jd)", argv[3], (intmax_t)offset);
        if ((cpfbz2 = BZ2_bzReadOpen(&cbz2err, cpf, 0, 0, NULL, 0)) == NULL)
                errx(1, "BZ2_bzReadOpen, bz2err = %d", cbz2err);
        offset = add_off_t(offset, bzctrllen);
        if (fseeko(dpf, offset, SEEK_SET))
                err(1, "fseeko(%s, %jd)", argv[3], (intmax_t)offset);
        if ((dpfbz2 = BZ2_bzReadOpen(&dbz2err, dpf, 0, 0, NULL, 0)) == NULL)
                errx(1, "BZ2_bzReadOpen, bz2err = %d", dbz2err);
        offset = add_off_t(offset, bzdatalen);
        if (fseeko(epf, offset, SEEK_SET))
                err(1, "fseeko(%s, %jd)", argv[3], (intmax_t)offset);
        if ((epfbz2 = BZ2_bzReadOpen(&ebz2err, epf, 0, 0, NULL, 0)) == NULL)
                errx(1, "BZ2_bzReadOpen, bz2err = %d", ebz2err);

        if ((oldsize = lseek(oldfd, 0, SEEK_END)) == -1 ||
            oldsize > SSIZE_MAX)
                err(1, "%s", argv[1]);

        old = mmap(NULL, oldsize+1, PROT_READ, MAP_SHARED, oldfd, 0);
        if (old == MAP_FAILED || close(oldfd) != 0)
                err(1, "%s", argv[1]);

        if ((new = malloc(newsize)) == NULL)
                err(1, NULL);

        oldpos = 0;
        newpos = 0;
        while (newpos < newsize) {
                /* Read control data */
                for (i = 0; i <= 2; i++) {
                        lenread = BZ2_bzRead(&cbz2err, cpfbz2, buf, 8);
                        if ((lenread < 8) || ((cbz2err != BZ_OK) &&
                            (cbz2err != BZ_STREAM_END)))
                                errx(1, "Corrupt patch");
                        ctrl[i] = offtin(buf);
                }

                /* Sanity-check */
                if (ctrl[0] < 0 || ctrl[0] > INT_MAX ||
                    ctrl[1] < 0 || ctrl[1] > INT_MAX)
                        errx(1, "Corrupt patch");

                /* Sanity-check */
                if (add_off_t(newpos, ctrl[0]) > newsize)
                        errx(1, "Corrupt patch");

                /* Read diff string */
                lenread = BZ2_bzRead(&dbz2err, dpfbz2, new + newpos, ctrl[0]);
                if ((lenread < ctrl[0]) ||
                    ((dbz2err != BZ_OK) && (dbz2err != BZ_STREAM_END)))
                        errx(1, "Corrupt patch");

                /* Add old data to diff string */
                for (i = 0; i < ctrl[0]; i++)
                        if (add_off_t(oldpos, i) < oldsize)
                                new[newpos + i] += old[oldpos + i];

                /* Adjust pointers */
                newpos = add_off_t(newpos, ctrl[0]);
                oldpos = add_off_t(oldpos, ctrl[0]);

                /* Sanity-check */
                if (add_off_t(newpos, ctrl[1]) > newsize)
                        errx(1, "Corrupt patch");

                /* Read extra string */
                lenread = BZ2_bzRead(&ebz2err, epfbz2, new + newpos, ctrl[1]);
                if ((lenread < ctrl[1]) ||
                    ((ebz2err != BZ_OK) && (ebz2err != BZ_STREAM_END)))
                        errx(1, "Corrupt patch");

                /* Adjust pointers */
                newpos = add_off_t(newpos, ctrl[1]);
                oldpos = add_off_t(oldpos, ctrl[2]);
        }

        /* Clean up the bzip2 reads */
        BZ2_bzReadClose(&cbz2err, cpfbz2);
        BZ2_bzReadClose(&dbz2err, dpfbz2);
        BZ2_bzReadClose(&ebz2err, epfbz2);
        if (fclose(cpf) || fclose(dpf) || fclose(epf))
                err(1, "fclose(%s)", argv[3]);

        /* Write the new file */
        if (write(newfd, new, newsize) != newsize || close(newfd) == -1)
                err(1, "%s", argv[2]);
        /* Disable atexit cleanup */
        newfile = NULL;

        free(new);
        munmap(old, oldsize+1);

        return (0);
}