/* vi: set sw=4 ts=4: */
/*
 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
 *
 * FIXME:
 *    In privileged mode if uname and gname map to a uid and gid then use the
 *    mapped value instead of the uid/gid values in tar header
 *
 * References:
 *    GNU tar and star man pages,
 *    Opengroup's ustar interchange format,
 *    http://www.opengroup.org/onlinepubs/007904975/utilities/pax.html
 */
#include "libbb.h"
#include "bb_archive.h"

typedef uint32_t aliased_uint32_t FIX_ALIASING;
typedef off_t    aliased_off_t    FIX_ALIASING;

/* NB: _DESTROYS_ str[len] character! */
static unsigned long long getOctal(char *str, int len)
{
        unsigned long long v;
        char *end;
        /* NB: leading spaces are allowed. Using strtoull to handle that.
         * The downside is that we accept e.g. "-123" too :(
         */
        str[len] = '\0';
        v = strtoull(str, &end, 8);
        /* std: "Each numeric field is terminated by one or more
         * <space> or NUL characters". We must support ' '! */
        if (*end != '\0' && *end != ' ') {
                int8_t first = str[0];
                if (!(first & 0x80))
                        bb_simple_error_msg_and_die("corrupted octal value in tar header");
                /*
                 * GNU tar uses "base-256 encoding" for very large numbers.
                 * Encoding is binary, with highest bit always set as a marker
                 * and sign in next-highest bit:
                 * 80 00 .. 00 - zero
                 * bf ff .. ff - largest positive number
                 * ff ff .. ff - minus 1
                 * c0 00 .. 00 - smallest negative number
                 *
                 * Example of tar file with 8914993153 (0x213600001) byte file.
                 * Field starts at offset 7c:
                 * 00070  30 30 30 00 30 30 30 30  30 30 30 00 80 00 00 00  |000.0000000.....|
                 * 00080  00 00 00 02 13 60 00 01  31 31 31 32 30 33 33 36  |.....`..11120336|
                 *
                 * NB: tarballs with NEGATIVE unix times encoded that way were seen!
                 */
                /* Sign-extend 7bit 'first' to 64bit 'v' (that is, using 6th bit as sign): */
                first <<= 1;
                first >>= 1; /* now 7th bit = 6th bit */
                v = first;   /* sign-extend 8 bits to 64 */
                while (--len != 0)
                        v = (v << 8) + (uint8_t) *++str;
        }
        return v;
}
#define GET_OCTAL(a) getOctal((a), sizeof(a))

#define TAR_EXTD (ENABLE_FEATURE_TAR_GNU_EXTENSIONS || ENABLE_FEATURE_TAR_SELINUX)
#if !TAR_EXTD
#define process_pax_hdr(archive_handle, sz, global) \
        process_pax_hdr(archive_handle, sz)
#endif
/* "global" is 0 or 1 */
static void process_pax_hdr(archive_handle_t *archive_handle, unsigned sz, int global)
{
#if !TAR_EXTD
        unsigned blk_sz = (sz + 511) & (~511);
        seek_by_read(archive_handle->src_fd, blk_sz);
#else
        unsigned blk_sz = (sz + 511) & (~511);
        char *buf, *p;

        p = buf = xmalloc(blk_sz + 1);
        xread(archive_handle->src_fd, buf, blk_sz);
        archive_handle->offset += blk_sz;

        /* prevent bb_strtou from running off the buffer */
        buf[sz] = '\0';

        while (sz != 0) {
                char *end, *value;
                unsigned len;

                /* Every record has this format: "LEN NAME=VALUE\n" */
                len = bb_strtou(p, &end, 10);
                /* expect errno to be EINVAL, because the character
                 * following the digits should be a space
                 */
                p += len;
                sz -= len;
                if (
                /** (int)sz < 0 - not good enough for huge malicious VALUE of 2^32-1 */
                    (int)(sz|len) < 0 /* this works */
                 || len == 0
                 || errno != EINVAL
                 || *end != ' '
                ) {
                        bb_simple_error_msg("malformed extended header, skipped");
                        // More verbose version:
                        //bb_error_msg("malformed extended header at %"OFF_FMT"d, skipped",
                        //              archive_handle->offset - (sz + len));
                        break;
                }
                /* overwrite the terminating newline with NUL
                 * (we do not bother to check that it *was* a newline)
                 */
                p[-1] = '\0';
                value = end + 1;

# if ENABLE_FEATURE_TAR_GNU_EXTENSIONS
                if (!global) {
                        if (is_prefixed_with(value, "path=")) {
                                value += sizeof("path=") - 1;
                                free(archive_handle->tar__longname);
                                archive_handle->tar__longname = xstrdup(value);
                                continue;
                        }
                        if (is_prefixed_with(value, "linkpath=")) {
                                value += sizeof("linkpath=") - 1;
                                free(archive_handle->tar__linkname);
                                archive_handle->tar__linkname = xstrdup(value);
                                continue;
                        }
                }
# endif

# if ENABLE_FEATURE_TAR_SELINUX
                /* Scan for SELinux contexts, via "RHT.security.selinux" keyword.
                 * This is what Red Hat's patched version of tar uses.
                 */
#  define SELINUX_CONTEXT_KEYWORD "RHT.security.selinux"
                if (is_prefixed_with(value, SELINUX_CONTEXT_KEYWORD"=")) {
                        value += sizeof(SELINUX_CONTEXT_KEYWORD"=") - 1;
                        free(archive_handle->tar__sctx[global]);
                        archive_handle->tar__sctx[global] = xstrdup(value);
                        continue;
                }
# endif
        }

        free(buf);
#endif
}

#if ENABLE_FEATURE_TAR_GNU_EXTENSIONS
static void die_if_bad_fnamesize(off_t sz)
{
        if ((uoff_t)sz > 0xfff) /* more than 4k?! no funny business please */
                bb_simple_error_msg_and_die("bad archive");
}
#endif

char FAST_FUNC get_header_tar(archive_handle_t *archive_handle)
{
        file_header_t *file_header = archive_handle->file_header;
        struct tar_header_t tar;
        char *cp;
        int tar_typeflag; /* can be "char", "int" seems give smaller code */
        int i, sum_u, sum;
#if ENABLE_FEATURE_TAR_OLDSUN_COMPATIBILITY
        int sum_s;
#endif
        int parse_names;

        /* Our "private data" */
#if ENABLE_FEATURE_TAR_GNU_EXTENSIONS
# define p_longname (archive_handle->tar__longname)
# define p_linkname (archive_handle->tar__linkname)
#else
# define p_longname 0
# define p_linkname 0
#endif

#if ENABLE_FEATURE_TAR_GNU_EXTENSIONS || ENABLE_FEATURE_TAR_SELINUX
 again:
#endif
        /* Align header */
        data_align(archive_handle, 512);

 again_after_align:

#if ENABLE_DESKTOP || ENABLE_FEATURE_TAR_AUTODETECT
        /* to prevent misdetection of bz2 sig */
        *(aliased_uint32_t*)&tar = 0;
        i = full_read(archive_handle->src_fd, &tar, 512);
        /* If GNU tar sees EOF in above read, it says:
         * "tar: A lone zero block at N", where N = kilobyte
         * where EOF was met (not EOF block, actual EOF!),
         * and exits with EXIT_SUCCESS.
         * We will mimic exit(EXIT_SUCCESS), although we will not mimic
         * the message and we don't check whether we indeed
         * saw zero block directly before this. */
        if (i == 0) {
                /* GNU tar 1.29 will be silent if tar archive ends abruptly
                 * (if there are no zero blocks at all, and last read returns zero,
                 * not short read 0 < len < 512). Complain only if
                 * the very first read fails. Grrr.
                 */
                if (archive_handle->offset == 0)
                        bb_simple_error_msg("short read");
                /* this merely signals end of archive, not exit(1): */
                return EXIT_FAILURE;
        }
        if (i != 512) {
                IF_FEATURE_TAR_AUTODETECT(goto autodetect;)
                bb_simple_error_msg_and_die("short read");
        }

#else
        i = 512;
        xread(archive_handle->src_fd, &tar, i);
#endif
        archive_handle->offset += i;

        /* If there is no filename its an empty header */
        if (tar.name[0] == 0 && tar.prefix[0] == 0
        /* Have seen a tar archive with pax 'x' header supplying UTF8 filename,
         * with actual file having all name fields NUL-filled. Check this: */
         && !p_longname
        ) {
                if (archive_handle->tar__end) {
                        /* Second consecutive empty header - end of archive.
                         * Read until the end to empty the pipe from gz or bz2
                         */
                        while (full_read(archive_handle->src_fd, &tar, 512) == 512)
                                continue;
                        return EXIT_FAILURE; /* "end of archive" */
                }
                archive_handle->tar__end = 1;
                return EXIT_SUCCESS; /* "decoded one header" */
        }
        archive_handle->tar__end = 0;

        /* Check header has valid magic, "ustar" is for the proper tar,
         * five NULs are for the old tar format  */
        if (!is_prefixed_with(tar.magic, "ustar")
         && (!ENABLE_FEATURE_TAR_OLDGNU_COMPATIBILITY
             || memcmp(tar.magic, "\0\0\0\0", 5) != 0)
        ) {
#if ENABLE_FEATURE_TAR_AUTODETECT
 autodetect:
                /* Two different causes for lseek() != 0:
                 * unseekable fd (would like to support that too, but...),
                 * or not first block (false positive, it's not .gz/.bz2!) */
                if (lseek(archive_handle->src_fd, -i, SEEK_CUR) != 0)
                        goto err;
                if (setup_unzip_on_fd(archive_handle->src_fd, /*fail_if_not_compressed:*/ 0) != 0)
 err:
                        bb_simple_error_msg_and_die("invalid tar magic");
                archive_handle->offset = 0;
                goto again_after_align;
#endif
                bb_simple_error_msg_and_die("invalid tar magic");
        }

        /* Do checksum on headers.
         * POSIX says that checksum is done on unsigned bytes, but
         * Sun and HP-UX gets it wrong... more details in
         * GNU tar source. */
        sum_u = ' ' * sizeof(tar.chksum);
#if ENABLE_FEATURE_TAR_OLDSUN_COMPATIBILITY
        sum_s = sum_u;
#endif
        for (i = 0; i < 148; i++) {
                sum_u += ((unsigned char*)&tar)[i];
#if ENABLE_FEATURE_TAR_OLDSUN_COMPATIBILITY
                sum_s += ((signed char*)&tar)[i];
#endif
        }
        for (i = 156; i < 512; i++) {
                sum_u += ((unsigned char*)&tar)[i];
#if ENABLE_FEATURE_TAR_OLDSUN_COMPATIBILITY
                sum_s += ((signed char*)&tar)[i];
#endif
        }
        /* Most tarfiles have tar.chksum NUL or space terminated, but
         * github.com decided to be "special" and have unterminated field:
         * 0090: 30343300 30303031 33323731 30000000 |043.000132710...|
         *                                                ^^^^^^^^|
         * Need to use GET_OCTAL. This overwrites tar.typeflag ---+
         * (the '0' char immediately after chksum in example above) with NUL.
         */
        tar_typeflag = (uint8_t)tar.typeflag; /* save it */
        sum = GET_OCTAL(tar.chksum);
        if (sum_u != sum
            IF_FEATURE_TAR_OLDSUN_COMPATIBILITY(&& sum_s != sum)
        ) {
                bb_simple_error_msg_and_die("invalid tar header checksum");
        }

        /* GET_OCTAL trashes subsequent field, therefore we call it
         * on fields in reverse order */
        if (tar.devmajor[0]) {
                char t = tar.prefix[0];
                /* we trash prefix[0] here, but we DO need it later! */
                unsigned minor = GET_OCTAL(tar.devminor);
                unsigned major = GET_OCTAL(tar.devmajor);
                file_header->device = makedev(major, minor);
                tar.prefix[0] = t;
        }

        /* 0 is reserved for high perf file, treat as normal file */
        if (tar_typeflag == '\0') tar_typeflag = '0';
        parse_names = (tar_typeflag >= '0' && tar_typeflag <= '7');

        file_header->link_target = NULL;
        if (!p_linkname && parse_names && tar.linkname[0]) {
                file_header->link_target = xstrndup(tar.linkname, sizeof(tar.linkname));
                /* FIXME: what if we have non-link object with link_target? */
                /* Will link_target be free()ed? */
        }
#if ENABLE_FEATURE_TAR_UNAME_GNAME
        file_header->tar__uname = tar.uname[0] ? xstrndup(tar.uname, sizeof(tar.uname)) : NULL;
        file_header->tar__gname = tar.gname[0] ? xstrndup(tar.gname, sizeof(tar.gname)) : NULL;
#endif
        file_header->mtime = GET_OCTAL(tar.mtime);
        file_header->size = GET_OCTAL(tar.size);
        file_header->gid = GET_OCTAL(tar.gid);
        file_header->uid = GET_OCTAL(tar.uid);
        /* Set bits 0-11 of the files mode */
        file_header->mode = 07777 & GET_OCTAL(tar.mode);

        file_header->name = NULL;
        if (!p_longname && parse_names) {
                /* we trash mode[0] here, it's ok */
                //tar.name[sizeof(tar.name)] = '\0'; - gcc 4.3.0 would complain
                tar.mode[0] = '\0';
                if (tar.prefix[0]) {
                        /* and padding[0] */
                        //tar.prefix[sizeof(tar.prefix)] = '\0'; - gcc 4.3.0 would complain
                        tar.padding[0] = '\0';
                        file_header->name = concat_path_file(tar.prefix, tar.name);
                } else
                        file_header->name = xstrdup(tar.name);
        }

        switch (tar_typeflag) {
        case '1': /* hardlink */
                /* we mark hardlinks as regular files with zero size and a link name */
                file_header->mode |= S_IFREG;
                /* on size of link fields from star(4)
                 * ... For tar archives written by pre POSIX.1-1988
                 * implementations, the size field usually contains the size of
                 * the file and needs to be ignored as no data may follow this
                 * header type.  For POSIX.1-1988 compliant archives, the size
                 * field needs to be 0.  For POSIX.1-2001 compliant archives,
                 * the size field may be non zero, indicating that file data is
                 * included in the archive.
                 * i.e; always assume this is zero for safety.
                 */
                goto size0;
        case '7':
        /* case 0: */
        case '0':
#if ENABLE_FEATURE_TAR_OLDGNU_COMPATIBILITY
                if (file_header->name && last_char_is(file_header->name, '/')) {
                        goto set_dir;
                }
#endif
                file_header->mode |= S_IFREG;
                break;
        case '2':
                file_header->mode |= S_IFLNK;
                /* have seen tarballs with size field containing
                 * the size of the link target's name */
 size0:
                file_header->size = 0;
                break;
        case '3':
                file_header->mode |= S_IFCHR;
                goto size0; /* paranoia */
        case '4':
                file_header->mode |= S_IFBLK;
                goto size0;
        case '5':
 IF_FEATURE_TAR_OLDGNU_COMPATIBILITY(set_dir:)
                file_header->mode |= S_IFDIR;
                goto size0;
        case '6':
                file_header->mode |= S_IFIFO;
                goto size0;
        case 'g':       /* pax global header */
        case 'x': {     /* pax extended header */
                if ((uoff_t)file_header->size > 0xfffff) /* paranoia */
                        goto skip_ext_hdr;
                process_pax_hdr(archive_handle, file_header->size, (tar_typeflag == 'g'));
                goto again_after_align;
#if ENABLE_FEATURE_TAR_GNU_EXTENSIONS
/* See http://www.gnu.org/software/tar/manual/html_node/Extensions.html */
        case 'L':
                /* free: paranoia: tar with several consecutive longnames */
                free(p_longname);
                /* For paranoia reasons we allocate extra NUL char */
                die_if_bad_fnamesize(file_header->size);
                p_longname = xzalloc(file_header->size + 1);
                /* We read ASCIZ string, including NUL */
                xread(archive_handle->src_fd, p_longname, file_header->size);
                archive_handle->offset += file_header->size;
                /* return get_header_tar(archive_handle); */
                /* gcc 4.1.1 didn't optimize it into jump */
                /* so we will do it ourself, this also saves stack */
                goto again;
        case 'K':
                free(p_linkname);
                die_if_bad_fnamesize(file_header->size);
                p_linkname = xzalloc(file_header->size + 1);
                xread(archive_handle->src_fd, p_linkname, file_header->size);
                archive_handle->offset += file_header->size;
                /* return get_header_tar(archive_handle); */
                goto again;
/*
 *      case 'S':       // Sparse file
 * Was seen in the wild. Not supported (yet?).
 * See https://www.gnu.org/software/tar/manual/html_section/tar_92.html
 * for the format. (An "Old GNU Format" was seen, not PAX formats).
 */
//      case 'D':       /* GNU dump dir */
//      case 'M':       /* Continuation of multi volume archive */
//      case 'N':       /* Old GNU for names > 100 characters */
        case 'V':       /* Volume header */
                ; /* Fall through to skip it */
#endif
        }
 skip_ext_hdr:
        {
                off_t sz;
                bb_error_msg("warning: skipping header '%c'", tar_typeflag);
                sz = (file_header->size + 511) & ~(off_t)511;
                archive_handle->offset += sz;
                sz >>= 9; /* sz /= 512 but w/o contortions for signed div */
                while (sz--)
                        xread(archive_handle->src_fd, &tar, 512);
                /* return get_header_tar(archive_handle); */
                goto again_after_align;
        }
        default:
                bb_error_msg_and_die("unknown typeflag: 0x%x", tar_typeflag);
        }

#if ENABLE_FEATURE_TAR_GNU_EXTENSIONS
        if (p_longname) {
                file_header->name = p_longname;
                p_longname = NULL;
        }
        if (p_linkname) {
                file_header->link_target = p_linkname;
                p_linkname = NULL;
        }
#endif

        /* Everything up to and including last ".." component is stripped */
        overlapping_strcpy(file_header->name, strip_unsafe_prefix(file_header->name));
//TODO: do the same for file_header->link_target?

        /* Strip trailing '/' in directories */
        /* Must be done after mode is set as '/' is used to check if it's a directory */
        cp = last_char_is(file_header->name, '/');

        if (archive_handle->filter(archive_handle) == EXIT_SUCCESS) {
                archive_handle->action_header(/*archive_handle->*/ file_header);
                /* Note that we kill the '/' only after action_header() */
                /* (like GNU tar 1.15.1: verbose mode outputs "dir/dir/") */
                if (cp)
                        *cp = '\0';
                archive_handle->action_data(archive_handle);
                if (archive_handle->accept || archive_handle->reject
                 || (archive_handle->ah_flags & ARCHIVE_REMEMBER_NAMES)
                ) {
                        llist_add_to(&archive_handle->passed, file_header->name);
                } else /* Caller isn't interested in list of unpacked files */
                        free(file_header->name);
        } else {
                data_skip(archive_handle);
                free(file_header->name);
        }
        archive_handle->offset += file_header->size;

        free(file_header->link_target);
        /* Do not free(file_header->name)!
         * It might be inserted in archive_handle->passed - see above */
#if ENABLE_FEATURE_TAR_UNAME_GNAME
        free(file_header->tar__uname);
        free(file_header->tar__gname);
#endif
        return EXIT_SUCCESS; /* "decoded one header" */
}