# macOS xattr-acls extra stuff

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<details>

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```bash
rm -rf /tmp/test*
echo test >/tmp/test
chmod +a "everyone deny write,writeattr,writeextattr,writesecurity,chown" /tmp/test
./get_acls test
ACL for test:
!#acl 1
group:ABCDEFAB-CDEF-ABCD-EFAB-CDEF0000000C:everyone:12:deny:write,writeattr,writeextattr,writesecurity,chown

ACL in hex: \x21\x23\x61\x63\x6c\x20\x31\x0a\x67\x72\x6f\x75\x70\x3a\x41\x42\x43\x44\x45\x46\x41\x42\x2d\x43\x44\x45\x46\x2d\x41\x42\x43\x44\x2d\x45\x46\x41\x42\x2d\x43\x44\x45\x46\x30\x30\x30\x30\x30\x30\x30\x43\x3a\x65\x76\x65\x72\x79\x6f\x6e\x65\x3a\x31\x32\x3a\x64\x65\x6e\x79\x3a\x77\x72\x69\x74\x65\x2c\x77\x72\x69\x74\x65\x61\x74\x74\x72\x2c\x77\x72\x69\x74\x65\x65\x78\x74\x61\x74\x74\x72\x2c\x77\x72\x69\x74\x65\x73\x65\x63\x75\x72\x69\x74\x79\x2c\x63\x68\x6f\x77\x6e\x0a
```
<details>

<summary>Código de get_acls</summary>
```c
// gcc -o get_acls get_acls
#include <stdio.h>
#include <stdlib.h>
#include <sys/acl.h>

int main(int argc, char *argv[]) {
if (argc != 2) {
fprintf(stderr, "Usage: %s <filepath>\n", argv[0]);
return 1;
}

const char *filepath = argv[1];
acl_t acl = acl_get_file(filepath, ACL_TYPE_EXTENDED);
if (acl == NULL) {
perror("acl_get_file");
return 1;
}

char *acl_text = acl_to_text(acl, NULL);
if (acl_text == NULL) {
perror("acl_to_text");
acl_free(acl);
return 1;
}

printf("ACL for %s:\n%s\n", filepath, acl_text);

// Convert acl_text to hexadecimal and print it
printf("ACL in hex: ");
for (char *c = acl_text; *c != '\0'; c++) {
printf("\\x%02x", (unsigned char)*c);
}
printf("\n");

acl_free(acl);
acl_free(acl_text);
return 0;
}
```
```markdown
<details>
<summary>MacOS XATTR e ACLs</summary>

O sistema de arquivos do macOS suporta atributos estendidos (XATTRs) e listas de controle de acesso (ACLs) que podem ser usados para aumentar a segurança e controlar o acesso a arquivos e diretórios.

### Atributos Estendidos (XATTRs)

Os atributos estendidos permitem que você anexe metadados a arquivos. Isso pode ser útil para armazenar informações adicionais que não se encaixam nos atributos padrão do sistema de arquivos.

### Listas de Controle de Acesso (ACLs)

As ACLs fornecem um controle de acesso mais granular em comparação com as permissões tradicionais do Unix. Com as ACLs, você pode definir permissões específicas para usuários e grupos individuais.

### Usos Comuns

- **Segurança de Arquivos**: Use XATTRs para marcar arquivos sensíveis e ACLs para restringir o acesso a eles.
- **Auditoria**: Armazene informações de auditoria em XATTRs para rastrear alterações em arquivos críticos.

### Comandos Úteis

- Para visualizar atributos estendidos:
  ```bash
  xattr -l <arquivo>
  ```

- Para adicionar um atributo:
  ```bash
  xattr -w <atributo> <valor> <arquivo>
  ```

- Para visualizar ACLs:
  ```bash
  ls -le <arquivo>
  ```

- Para adicionar uma ACL:
  ```bash
  chmod +a "<usuário> allow <permissão>" <arquivo>
  ```

Essas técnicas podem ser usadas para melhorar a segurança do seu sistema e proteger dados sensíveis contra acesso não autorizado.

</details>
```
```bash
# Lets add the xattr com.apple.xxx.xxxx with the acls
mkdir start
mkdir start/protected
./set_xattr start/protected
echo something > start/protected/something
```
<details>

<summary>Código de set_xattr</summary>
```c
// gcc -o set_xattr set_xattr.c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/xattr.h>
#include <sys/acl.h>


void print_xattrs(const char *filepath) {
ssize_t buflen = listxattr(filepath, NULL, 0, XATTR_NOFOLLOW);
if (buflen < 0) {
perror("listxattr");
return;
}

char *buf = malloc(buflen);
if (buf == NULL) {
perror("malloc");
return;
}

buflen = listxattr(filepath, buf, buflen, XATTR_NOFOLLOW);
if (buflen < 0) {
perror("listxattr");
free(buf);
return;
}

printf("All current extended attributes for %s:\n", filepath);
for (char *name = buf; name < buf + buflen; name += strlen(name) + 1) {
printf("%s: ", name);
ssize_t valuelen = getxattr(filepath, name, NULL, 0, 0, XATTR_NOFOLLOW);
if (valuelen < 0) {
perror("getxattr");
continue;
}

char *value = malloc(valuelen + 1);
if (value == NULL) {
perror("malloc");
continue;
}

valuelen = getxattr(filepath, name, value, valuelen, 0, XATTR_NOFOLLOW);
if (valuelen < 0) {
perror("getxattr");
free(value);
continue;
}

value[valuelen] = '\0';  // Null-terminate the value
printf("%s\n", value);
free(value);
}

free(buf);
}


int main(int argc, char *argv[]) {
if (argc != 2) {
fprintf(stderr, "Usage: %s <filepath>\n", argv[0]);
return 1;
}

const char *hex = "\x21\x23\x61\x63\x6c\x20\x31\x0a\x67\x72\x6f\x75\x70\x3a\x41\x42\x43\x44\x45\x46\x41\x42\x2d\x43\x44\x45\x46\x2d\x41\x42\x43\x44\x2d\x45\x46\x41\x42\x2d\x43\x44\x45\x46\x30\x30\x30\x30\x30\x30\x30\x43\x3a\x65\x76\x65\x72\x79\x6f\x6e\x65\x3a\x31\x32\x3a\x64\x65\x6e\x79\x3a\x77\x72\x69\x74\x65\x2c\x77\x72\x69\x74\x65\x61\x74\x74\x72\x2c\x77\x72\x69\x74\x65\x65\x78\x74\x61\x74\x74\x72\x2c\x77\x72\x69\x74\x65\x73\x65\x63\x75\x72\x69\x74\x79\x2c\x63\x68\x6f\x77\x6e\x0a";
const char *filepath = argv[1];

int result = setxattr(filepath, "com.apple.xxx.xxxx", hex, strlen(hex), 0, 0);
if (result == 0) {
printf("Extended attribute set successfully.\n\n");
} else {
perror("setxattr");
return 1;
}

print_xattrs(filepath);

return 0;
}
```
</details>

{% code overflow="wrap" %}
```bash
# Create appledoublefile with the xattr entitlement
ditto -c -k start protected.zip
rm -rf start
# extract the files
unzip protected.zip
# Replace the name of the xattr here (if you put it before ditto would have destroyed it)
python3 -c "with open('._protected', 'rb+') as f: content = f.read().replace(b'com.apple.xxx.xxxx', b'com.apple.acl.text'); f.seek(0); f.write(content); f.truncate()"
# zip everything back together
rm -rf protected.zip
zip -r protected.zip protected ._protected
rm -rf protected
rm ._*
```
{% endcode %}
```bash
# Check if it worked
ditto -x -k --rsrc protected.zip .
xattr -l protected
```
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