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== Conferindo o sigilo == | |||
Agora lembra que coloquei na variável de senha da base de dados isso aqui '''PASS="tua_senha_aqui"''' ? Vamos checar se ela aparece em algum lugar no binário usando o programa '''strings,''' que existe na maioria das distribuições GNU/Linux, e permite extrair strings visíveis de dentro de binários. | Agora lembra que coloquei na variável de senha da base de dados isso aqui '''PASS="tua_senha_aqui"''' ? Vamos checar se ela aparece em algum lugar no binário usando o programa '''strings,''' que existe na maioria das distribuições GNU/Linux, e permite extrair strings visíveis de dentro de binários. | ||
# strings backup | grep "tua_senha_aqui" | # strings backup | grep "tua_senha_aqui" | ||
Edição das 15h21min de 5 de fevereiro de 2023
Introdução
Em algumas situações você pode querer que seu código escrito em shell script seja compilado por diversos motivos como por exemplo: esconder alguma informação sigilosa que está dentro do script, uma credencial de acesso à base de dados, ou porque você não quer que alguém altere o código sem a sua permissão, ou porque você não quer entregar o "ouro" da sua consultoria. Enfim, é uma maneira de esconder o seu código dos olhos alheios. Mas existem algumas coisas que temos que ter em mente quando formos usá-lo:
- Ele não é a prova de NSA (National Security Agency). Não possui uma criptografia de alto nível mas ajuda bastante na tarefa.
- Não gera binários independentes. Você continuará dependendo do shell e de todos os programas que ele chama.
- O SHC (Shell Script Compiler) precisa ter no topo do arquivo o shebang, a informação que aponta o shell que será usado, por exemplo: #!/usr/bin/bash ou #!/usr/bin/sh
- O SHC gera um código em fonte C do shell script, que na sequência é compilado. Sim você precisa ter um compilador C para isso. No processo de execução, o programa é desencriptado e executado como um bash normal; por isso não é um binário independente.
- Você pode colocar um prazo de validade do binário e uma mensagem para quem executar o programa após vencer a validade. Ex: "Programa expirado contacte fulano".
- O binário fica bem maior que o seu arquivo shell script.
- Não pense que a execução do seu novo binário será muito mais rápido que o seu shell, porque como eu disse, o processo é rodado como shell após ser desencriptado.
Instalação
Como é de hábito aqui, faremos isso no Debian, nesse caso a versão 11 (Bullseye). Você pode instalar o SHC em qualquer distribuição GNU/Linux de sua preferência, só precisará checar se já existe um pacote para ele ou se vai precisar compilar o fonte e logicamente ter um compilador C também instalado para isso.
apt install shc build-essential
Utilizando o SHC
Vou pegar como exemplo um script de backup que tenho aqui e que além de fazer backup dos arquivos e diretórios que tenho no servidor, ele gera um backup da base de dados e as tabelas separadamente.
#!/usr/bin/bash
SERVIDOR="azn"
PROVEDOR="Area Zero Network"
TEMP="/usr/local/backup/azn"
USER="root"
PASS="tua_senha_aqui"
dpkg -l > $TEMP/`date +%d`/lista_pacotes.txt
tar -czpf $TEMP/`date +%d`/$SERVIDOR.tar.gz /etc /root /var/www
tar -tzpf $TEMP/`date +%d`/$SERVIDOR.tar.gz
if [ $? -ne 0 ]; then
echo "Erro gerando backup AZN tar.gz!" | /usr/local/sbin/telegram-notify --error --text -
exit
fi
rm $TEMP/`date +%d`/*.bz2
for banco in $(mysql -u$USER -p$PASS --execute="show databases" | grep -v Database) ; do
for tabela in $(mysql -u$USER -p$PASS --execute="show tables" $banco | grep -v Tables_in_) ; do
if [ "$banco" == "mysql" -a "$tabela" == "general_log" ]; then
mysqldump -c -u$USER -p$PASS --lock-tables=0 $banco $tabela | bzip2 -9 > $TEMP/`date +%d`/$SERVIDOR-$banco-$tabela.sql.bz2
else
if [ "$banco" == "mysql" -a "$tabela" == "slow_log" ]; then
mysqldump -c -u$USER -p$PASS --lock-tables=0 $banco $tabela | bzip2 -9 > $TEMP/`date +%d`/$SERVIDOR-$banco-$tabela.sql.bz2
else
mysqldump -c -u$USER -p$PASS --single-transaction=TRUE $banco $tabela | bzip2 -9 > $TEMP/`date +%d`/$SERVIDOR-$banco-$tabela.sql.bz2
fi
fi
if [ $? -ne 0 ]; then
echo "Erro gerando backup AZN MariaDB!" | /usr/local/sbin/telegram-notify --error --text -
exit
fi
done
done
echo "Backup do servidor AZN feito corretamente!" | /usr/local/sbin/telegram-notify --success --text -
Esse script além de fazer o backup, me avisa pelo Telegram se foi tudo bem ou se deu algum erro. Percebam que ali na variável PASS teria a senha da base de dados para o backup e não é bom que fique assim disponível para qualquer um ver. Então vamos compilar nosso shell script assim, supondo que o nome dele seja backup.sh.
# shc -o backup -f backup.sh
Esse comando lerá o backup.sh, gerará nosso binário chamado backup e o fonte em C chamado backup.sh.x.c.
# ls -lah backup_* -rwxrwxr-x 1 root root 17K fev 5 14:19 backup -rwx------ 1 root root 1,5K fev 5 13:59 backup.sh -rw-r--r-- 1 root root 25K fev 5 14:19 backup.sh.x.c
Primeira coisa que reparamos é o tamanho de cada arquivo; nosso backup.sh possui um apenas 1,5k de tamanho enquanto o binário ficou com 17k. Mas não vamos ser mesquinhos quanto a isso, porque na maioria das vezes temos bastante recurso de memória nos servidores que mexemos não é mesmo?
Após a execução do binário
Para testar rodei o binário, este fez todo o backup e por fim ainda avisou no meu Telegram. Obs.: em outro artigo mostrarei como configurar esse programa que uso para o Telegram.
Código fonte em C
Vamos olhar como ficou nosso fonte em C?
#if 0
shc Version 4.0.3, Generic Shell Script Compiler
GNU GPL Version 3 Md Jahidul Hamid <[email protected]>
shc -o backup -f backup.sh
#endif
static char data [] =
#define chk2_z 19
#define chk2 ((&data[3]))
"\132\367\223\065\273\354\372\026\336\302\175\261\134\337\354\357"
"\375\203\257\174\303\036"
#define msg2_z 19
#define msg2 ((&data[26]))
"\155\236\003\175\207\220\316\347\020\101\333\207\160\021\241\204"
"\017\071\370\357\256\164\171\203\210"
#define tst1_z 22
#define tst1 ((&data[47]))
"\230\215\223\271\263\242\067\162\123\145\022\201\376\321\007\232"
"\336\205\051\005\242\301\356\243\232\046\200"
#define rlax_z 1
#define rlax ((&data[74]))
"\166"
#define opts_z 1
#define opts ((&data[75]))
"\315"
#define xecc_z 15
#define xecc ((&data[76]))
"\355\244\240\352\251\255\145\034\004\045\341\147\267\353\330\001"
"\113"
#define text_z 1447
#define text ((&data[445]))
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"\110\250"
#define pswd_z 256
#define pswd ((&data[2264]))
"\206\174\026\011\356\071\161\175\153\356\161\041\262\167\243\133"
"\063\264\047\236\007\253\254\223\141\220\334\012\226\276\135\034"
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"\102\260\037\225\260\021\146\213\351\050\247\256\346\330\102\332"
"\302\150\316\065\004\123\026\076\127\067\376\323\133\007\317\236"
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"\103\122\154\107\246\202\205\375\272\204\321\026\214\240\264\105"
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"\305\130\167\154\333\375\152\225\201\073\253\015\334\140\123\153"
"\110\001\373\312\245\164\020\345\205\377\231\161\162\205\240\067"
"\335\027\244\270\024\016\116\226\112\012\324\064\311\061\121\004"
"\246\170\055\124\020\324\155\230\354\250\322\174\207\147"
#define shll_z 14
#define shll ((&data[2541]))
"\201\333\141\250\373\350\322\221\324\376\333\204\172\165"
#define tst2_z 19
#define tst2 ((&data[2558]))
"\255\342\127\230\174\067\202\133\305\341\056\052\041\216\246\161"
"\266\045\220\035\116\151\114\355"
#define date_z 1
#define date ((&data[2579]))
"\173"
#define lsto_z 1
#define lsto ((&data[2580]))
"\061"
#define msg1_z 65
#define msg1 ((&data[2585]))
"\130\134\275\306\206\170\220\063\325\271\325\374\376\070\240\216"
"\263\032\004\000\156\271\123\225\240\070\024\223\202\157\071\257"
"\103\314\022\152\374\277\174\330\076\251\125\113\033\155\230\356"
"\032\306\005\320\306\227\244\323\257\032\172\026\305\153\101\147"
"\346\271\102\230\037\364\251\157\306\045\366\056\144\020\123\004"
"\304\340\262\247"
#define inlo_z 3
#define inlo ((&data[2665]))
"\054\131\301"
#define chk1_z 22
#define chk1 ((&data[2670]))
"\300\122\272\277\177\234\273\371\140\206\142\100\226\064\304\245"
"\163\143\142\034\026\135\015\306\006"/* End of data[] */;
#define hide_z 4096
#define SETUID 0 /* Define as 1 to call setuid(0) at start of script */
#define DEBUGEXEC 0 /* Define as 1 to debug execvp calls */
#define TRACEABLE 1 /* Define as 1 to enable ptrace the executable */
#define HARDENING 0 /* Define as 1 to disable ptrace/dump the executable */
#define BUSYBOXON 0 /* Define as 1 to enable work with busybox */
#if HARDENING
static const char * shc_x[] = {
"/*",
" * Copyright 2019 - Intika <[email protected]>",
" * Replace ******** with secret read from fd 21",
" * Also change arguments location of sub commands (sh script commands)",
" * gcc -Wall -fpic -shared -o shc_secret.so shc_secret.c -ldl",
" */",
"",
"#define _GNU_SOURCE /* needed to get RTLD_NEXT defined in dlfcn.h */",
"#define PLACEHOLDER \"********\"",
"#include <dlfcn.h>",
"#include <stdlib.h>",
"#include <string.h>",
"#include <unistd.h>",
"#include <stdio.h>",
"#include <signal.h>",
"",
"static char secret[128000]; //max size",
"typedef int (*pfi)(int, char **, char **);",
"static pfi real_main;",
"",
"// copy argv to new location",
"char **copyargs(int argc, char** argv){",
" char **newargv = malloc((argc+1)*sizeof(*argv));",
" char *from,*to;",
" int i,len;",
"",
" for(i = 0; i<argc; i++){",
" from = argv[i];",
" len = strlen(from)+1;",
" to = malloc(len);",
" memcpy(to,from,len);",
" // zap old argv space",
" memset(from,'\\0',len);",
" newargv[i] = to;",
" argv[i] = 0;",
" }",
" newargv[argc] = 0;",
" return newargv;",
"}",
"",
"static int mymain(int argc, char** argv, char** env) {",
" //fprintf(stderr, \"Inject main argc = %d\\n\", argc);",
" return real_main(argc, copyargs(argc,argv), env);",
"}",
"",
"int __libc_start_main(int (*main) (int, char**, char**),",
" int argc,",
" char **argv,",
" void (*init) (void),",
" void (*fini)(void),",
" void (*rtld_fini)(void),",
" void (*stack_end)){",
" static int (*real___libc_start_main)() = NULL;",
" int n;",
"",
" if (!real___libc_start_main) {",
" real___libc_start_main = dlsym(RTLD_NEXT, \"__libc_start_main\");",
" if (!real___libc_start_main) abort();",
" }",
"",
" n = read(21, secret, sizeof(secret));",
" if (n > 0) {",
" int i;",
"",
" if (secret[n - 1] == '\\n') secret[--n] = '\\0';",
" for (i = 1; i < argc; i++)",
" if (strcmp(argv[i], PLACEHOLDER) == 0)",
" argv[i] = secret;",
" }",
"",
" real_main = main;",
"",
" return real___libc_start_main(mymain, argc, argv, init, fini, rtld_fini, stack_end);",
"}",
"",
0};
#endif /* HARDENING */
/* rtc.c */
#include <sys/stat.h>
#include <sys/types.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <unistd.h>
/* 'Alleged RC4' */
static unsigned char stte[256], indx, jndx, kndx;
/*
* Reset arc4 stte.
*/
void stte_0(void)
{
indx = jndx = kndx = 0;
do {
stte[indx] = indx;
} while (++indx);
}
/*
* Set key. Can be used more than once.
*/
void key(void * str, int len)
{
unsigned char tmp, * ptr = (unsigned char *)str;
while (len > 0) {
do {
tmp = stte[indx];
kndx += tmp;
kndx += ptr[(int)indx % len];
stte[indx] = stte[kndx];
stte[kndx] = tmp;
} while (++indx);
ptr += 256;
len -= 256;
}
}
/*
* Crypt data.
*/
void arc4(void * str, int len)
{
unsigned char tmp, * ptr = (unsigned char *)str;
while (len > 0) {
indx++;
tmp = stte[indx];
jndx += tmp;
stte[indx] = stte[jndx];
stte[jndx] = tmp;
tmp += stte[indx];
*ptr ^= stte[tmp];
ptr++;
len--;
}
}
/* End of ARC4 */
#if HARDENING
#include <sys/ptrace.h>
#include <sys/wait.h>
#include <signal.h>
#include <sys/prctl.h>
#define PR_SET_PTRACER 0x59616d61
/* Seccomp Sandboxing Init */
#include <stdlib.h>
#include <stdio.h>
#include <stddef.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/prctl.h>
#include <sys/syscall.h>
#include <sys/socket.h>
#include <linux/filter.h>
#include <linux/seccomp.h>
#include <linux/audit.h>
#define ArchField offsetof(struct seccomp_data, arch)
#define Allow(syscall) \
BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, SYS_##syscall, 0, 1), \
BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW)
struct sock_filter filter[] = {
/* validate arch */
BPF_STMT(BPF_LD+BPF_W+BPF_ABS, ArchField),
BPF_JUMP( BPF_JMP+BPF_JEQ+BPF_K, AUDIT_ARCH_X86_64, 1, 0),
BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_KILL),
/* load syscall */
BPF_STMT(BPF_LD+BPF_W+BPF_ABS, offsetof(struct seccomp_data, nr)),
/* list of allowed syscalls */
Allow(exit_group), /* exits a process */
Allow(brk), /* for malloc(), inside libc */
Allow(mmap), /* also for malloc() */
Allow(munmap), /* for free(), inside libc */
/* and if we don't match above, die */
BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_KILL),
};
struct sock_fprog filterprog = {
.len = sizeof(filter)/sizeof(filter[0]),
.filter = filter
};
/* Seccomp Sandboxing - Set up the restricted environment */
void seccomp_hardening() {
if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
perror("Could not start seccomp:");
exit(1);
}
if (prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &filterprog) == -1) {
perror("Could not start seccomp:");
exit(1);
}
}
/* End Seccomp Sandboxing Init */
void shc_x_file() {
FILE *fp;
int line = 0;
if ((fp = fopen("/tmp/shc_x.c", "w")) == NULL ) {exit(1); exit(1);}
for (line = 0; shc_x[line]; line++) fprintf(fp, "%s\n", shc_x[line]);
fflush(fp);fclose(fp);
}
int make() {
char * cc, * cflags, * ldflags;
char cmd[4096];
cc = getenv("CC");
if (!cc) cc = "cc";
sprintf(cmd, "%s %s -o %s %s", cc, "-Wall -fpic -shared", "/tmp/shc_x.so", "/tmp/shc_x.c -ldl");
if (system(cmd)) {remove("/tmp/shc_x.c"); return -1;}
remove("/tmp/shc_x.c"); return 0;
}
void arc4_hardrun(void * str, int len) {
//Decode locally
char tmp2[len];
char tmp3[len+1024];
memcpy(tmp2, str, len);
unsigned char tmp, * ptr = (unsigned char *)tmp2;
int lentmp = len;
int pid, status;
pid = fork();
shc_x_file();
if (make()) {exit(1);}
setenv("LD_PRELOAD","/tmp/shc_x.so",1);
if(pid==0) {
//Start tracing to protect from dump & trace
if (ptrace(PTRACE_TRACEME, 0, 0, 0) < 0) {
kill(getpid(), SIGKILL);
_exit(1);
}
//Decode Bash
while (len > 0) {
indx++;
tmp = stte[indx];
jndx += tmp;
stte[indx] = stte[jndx];
stte[jndx] = tmp;
tmp += stte[indx];
*ptr ^= stte[tmp];
ptr++;
len--;
}
//Do the magic
sprintf(tmp3, "%s %s", "'********' 21<<<", tmp2);
//Exec bash script //fork execl with 'sh -c'
system(tmp2);
//Empty script variable
memcpy(tmp2, str, lentmp);
//Clean temp
remove("/tmp/shc_x.so");
//Sinal to detach ptrace
ptrace(PTRACE_DETACH, 0, 0, 0);
exit(0);
}
else {wait(&status);}
/* Seccomp Sandboxing - Start */
seccomp_hardening();
exit(0);
}
#endif /* HARDENING */
/*
* Key with file invariants.
*/
int key_with_file(char * file)
{
struct stat statf[1];
struct stat control[1];
if (stat(file, statf) < 0)
return -1;
/* Turn on stable fields */
memset(control, 0, sizeof(control));
control->st_ino = statf->st_ino;
control->st_dev = statf->st_dev;
control->st_rdev = statf->st_rdev;
control->st_uid = statf->st_uid;
control->st_gid = statf->st_gid;
control->st_size = statf->st_size;
control->st_mtime = statf->st_mtime;
control->st_ctime = statf->st_ctime;
key(control, sizeof(control));
return 0;
}
#if DEBUGEXEC
void debugexec(char * sh11, int argc, char ** argv)
{
int i;
fprintf(stderr, "shll=%s\n", sh11 ? sh11 : "<null>");
fprintf(stderr, "argc=%d\n", argc);
if (!argv) {
fprintf(stderr, "argv=<null>\n");
} else {
for (i = 0; i <= argc ; i++)
fprintf(stderr, "argv[%d]=%.60s\n", i, argv[i] ? argv[i] : "<null>");
}
}
#endif /* DEBUGEXEC */
void rmarg(char ** argv, char * arg)
{
for (; argv && *argv && *argv != arg; argv++);
for (; argv && *argv; argv++)
*argv = argv[1];
}
void chkenv_end(void);
int chkenv(int argc)
{
char buff[512];
unsigned long mask, m;
int l, a, c;
char * string;
extern char ** environ;
mask = (unsigned long)getpid();
stte_0();
key(&chkenv, (void*)&chkenv_end - (void*)&chkenv);
key(&data, sizeof(data));
key(&mask, sizeof(mask));
arc4(&mask, sizeof(mask));
sprintf(buff, "x%lx", mask);
string = getenv(buff);
#if DEBUGEXEC
fprintf(stderr, "getenv(%s)=%s\n", buff, string ? string : "<null>");
#endif
l = strlen(buff);
if (!string) {
/* 1st */
sprintf(&buff[l], "=%lu %d", mask, argc);
putenv(strdup(buff));
return 0;
}
c = sscanf(string, "%lu %d%c", &m, &a, buff);
if (c == 2 && m == mask) {
/* 3rd */
rmarg(environ, &string[-l - 1]);
return 1 + (argc - a);
}
return -1;
}
void chkenv_end(void){}
#if HARDENING
static void gets_process_name(const pid_t pid, char * name) {
char procfile[BUFSIZ];
sprintf(procfile, "/proc/%d/cmdline", pid);
FILE* f = fopen(procfile, "r");
if (f) {
size_t size;
size = fread(name, sizeof (char), sizeof (procfile), f);
if (size > 0) {
if ('\n' == name[size - 1])
name[size - 1] = '\0';
}
fclose(f);
}
}
void hardening() {
prctl(PR_SET_DUMPABLE, 0);
prctl(PR_SET_PTRACER, -1);
int pid = getppid();
char name[256] = {0};
gets_process_name(pid, name);
if ( (strcmp(name, "bash") != 0)
&& (strcmp(name, "/bin/bash") != 0)
&& (strcmp(name, "sh") != 0)
&& (strcmp(name, "/bin/sh") != 0)
&& (strcmp(name, "sudo") != 0)
&& (strcmp(name, "/bin/sudo") != 0)
&& (strcmp(name, "/usr/bin/sudo") != 0)
&& (strcmp(name, "gksudo") != 0)
&& (strcmp(name, "/bin/gksudo") != 0)
&& (strcmp(name, "/usr/bin/gksudo") != 0)
&& (strcmp(name, "kdesu") != 0)
&& (strcmp(name, "/bin/kdesu") != 0)
&& (strcmp(name, "/usr/bin/kdesu") != 0)
)
{
printf("Operation not permitted\n");
kill(getpid(), SIGKILL);
exit(1);
}
}
#endif /* HARDENING */
#if !TRACEABLE
#define _LINUX_SOURCE_COMPAT
#include <sys/ptrace.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <fcntl.h>
#include <signal.h>
#include <stdio.h>
#include <unistd.h>
#if !defined(PT_ATTACHEXC) /* New replacement for PT_ATTACH */
#if !defined(PTRACE_ATTACH) && defined(PT_ATTACH)
#define PT_ATTACHEXC PT_ATTACH
#elif defined(PTRACE_ATTACH)
#define PT_ATTACHEXC PTRACE_ATTACH
#endif
#endif
void untraceable(char * argv0)
{
char proc[80];
int pid, mine;
switch(pid = fork()) {
case 0:
pid = getppid();
/* For problematic SunOS ptrace */
#if defined(__FreeBSD__)
sprintf(proc, "/proc/%d/mem", (int)pid);
#else
sprintf(proc, "/proc/%d/as", (int)pid);
#endif
close(0);
mine = !open(proc, O_RDWR|O_EXCL);
if (!mine && errno != EBUSY)
mine = !ptrace(PT_ATTACHEXC, pid, 0, 0);
if (mine) {
kill(pid, SIGCONT);
} else {
perror(argv0);
kill(pid, SIGKILL);
}
_exit(mine);
case -1:
break;
default:
if (pid == waitpid(pid, 0, 0))
return;
}
perror(argv0);
_exit(1);
}
#endif /* !TRACEABLE */
char * xsh(int argc, char ** argv)
{
char * scrpt;
int ret, i, j;
char ** varg;
char * me = argv[0];
if (me == NULL) { me = getenv("_"); }
if (me == 0) { fprintf(stderr, "E: neither argv[0] nor $_ works."); exit(1); }
ret = chkenv(argc);
stte_0();
key(pswd, pswd_z);
arc4(msg1, msg1_z);
arc4(date, date_z);
if (date[0] && (atoll(date)<time(NULL)))
return msg1;
arc4(shll, shll_z);
arc4(inlo, inlo_z);
arc4(xecc, xecc_z);
arc4(lsto, lsto_z);
arc4(tst1, tst1_z);
key(tst1, tst1_z);
arc4(chk1, chk1_z);
if ((chk1_z != tst1_z) || memcmp(tst1, chk1, tst1_z))
return tst1;
arc4(msg2, msg2_z);
if (ret < 0)
return msg2;
varg = (char **)calloc(argc + 10, sizeof(char *));
if (!varg)
return 0;
if (ret) {
arc4(rlax, rlax_z);
if (!rlax[0] && key_with_file(shll))
return shll;
arc4(opts, opts_z);
#if HARDENING
arc4_hardrun(text, text_z);
exit(0);
/* Seccomp Sandboxing - Start */
seccomp_hardening();
#endif
arc4(text, text_z);
arc4(tst2, tst2_z);
key(tst2, tst2_z);
arc4(chk2, chk2_z);
if ((chk2_z != tst2_z) || memcmp(tst2, chk2, tst2_z))
return tst2;
/* Prepend hide_z spaces to script text to hide it. */
scrpt = malloc(hide_z + text_z);
if (!scrpt)
return 0;
memset(scrpt, (int) ' ', hide_z);
memcpy(&scrpt[hide_z], text, text_z);
} else { /* Reexecute */
if (*xecc) {
scrpt = malloc(512);
if (!scrpt)
return 0;
sprintf(scrpt, xecc, me);
} else {
scrpt = me;
}
}
j = 0;
#if BUSYBOXON
varg[j++] = "busybox";
varg[j++] = "sh";
#else
varg[j++] = argv[0]; /* My own name at execution */
#endif
if (ret && *opts)
varg[j++] = opts; /* Options on 1st line of code */
if (*inlo)
varg[j++] = inlo; /* Option introducing inline code */
varg[j++] = scrpt; /* The script itself */
if (*lsto)
varg[j++] = lsto; /* Option meaning last option */
i = (ret > 1) ? ret : 0; /* Args numbering correction */
while (i < argc)
varg[j++] = argv[i++]; /* Main run-time arguments */
varg[j] = 0; /* NULL terminated array */
#if DEBUGEXEC
debugexec(shll, j, varg);
#endif
execvp(shll, varg);
return shll;
}
int main(int argc, char ** argv)
{
#if SETUID
setuid(0);
#endif
#if DEBUGEXEC
debugexec("main", argc, argv);
#endif
#if HARDENING
hardening();
#endif
#if !TRACEABLE
untraceable(argv[0]);
#endif
argv[1] = xsh(argc, argv);
fprintf(stderr, "%s%s%s: %s\n", argv[0],
errno ? ": " : "",
errno ? strerror(errno) : "",
argv[1] ? argv[1] : "<null>"
);
return 1;
}
Conferindo o sigilo
Agora lembra que coloquei na variável de senha da base de dados isso aqui PASS="tua_senha_aqui" ? Vamos checar se ela aparece em algum lugar no binário usando o programa strings, que existe na maioria das distribuições GNU/Linux, e permite extrair strings visíveis de dentro de binários.
# strings backup | grep "tua_senha_aqui" #
Como pudemos ver, não foi encontrada a senha no binário mas ela encontra-se codificada no fonte em C; então não esqueça de apagar o fonte.
Colocando um prazo de validade no binário
Para colocarmos um prazo de validade no binário façamos assim como exemplo. A data é no formato dd/mm/yyyy (dia/mês/ano).
shc -e 04/03/2023 -m "Seu programa expirou falar com fulano" -o backup -f backup.sh
Dessa data em diante ao executar o binário irá aparecer a mensagem que colocamos.
# ./backup ./backup: has expired! Seu programa expirou falar com fulano
Finalizando
Basicamente é isso que o SHC faz, acho bem útil para determinadas situações e acredito que possa ajudá-lo em algo nesse sentido. Lembre-se que compartilhar conhecimento é uma via de duas mãos e procure contribuir com seus códigos também. Procure usar esse artifício para necessidades que envolvam um pouco mais de segurança na sua administração de sistemas.
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