exile.h/qssb.h

588 خطوط
13 KiB
C

#ifndef QSSB_H
#define QSSB_H
#ifndef _GNU_SOURCE
#define _GNU_SOURCE
#endif
#include <sched.h>
#include <stdio.h>
#include <errno.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/mount.h>
#include <sys/prctl.h>
#include <sys/random.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <linux/limits.h>
#include <linux/filter.h>
#include <linux/seccomp.h>
#include <sys/capability.h>
#include <stddef.h>
#include <inttypes.h>
#include <asm/unistd.h>
//TODO: stolen from kernel samples/seccomp, GPLv2...?
#define ALLOW \
BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW)
#define DENY \
BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_KILL)
#define SYSCALL(nr, jt) \
BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (nr), 0, 1), jt
#define LOAD_SYSCALL_NR \
BPF_STMT(BPF_LD+BPF_W+BPF_ABS, \
offsetof(struct seccomp_data, nr))
#define QSSB_UNSHARE_NETWORK 1<<1
#define QSSB_UNSHARE_USER 1<<2
#define QSSB_UNSHARE_MOUNT 1<<3
#ifndef QSSB_LOG_ERROR
#define QSSB_LOG_ERROR(...) fprintf(stderr, __VA_ARGS__)
#endif
#ifndef QSSB_TEMP_DIR
#define QSSB_TEMP_DIR "/tmp"
#endif
#define QSSB_SYS(x) (__NR_##x)
//TODO: implement
#define QSSB_MOUNT_ALLOW_NOTHING 0 //explicit rule
#define QSSB_MOUNT_ALLOW_READ 1<<0
#define QSSB_MOUNT_ALLOW_WRITE (1<<1) | QSSB_MOUNT_ALLOW_READ
#define QSSB_MOUNT_ALLOW_EXEC 1<<2
#define QSSB_MOUNT_ALLOW_DEV 1<<3
#define QSSB_MOUNT_ALLOW_SETUID 1<<4
//don't mount recursive
#define QSSB_MOUNT_NOT_REC 1<<5
/* Most exploits have more need for those syscalls than the
* exploited programs. In cases they are needed, this list should be
* filtered or simply not used.
*/
/* TODO: more execv* in some architectures */
/* TODO: add more */
static int default_blacklisted_syscals[] = {
QSSB_SYS(setuid),
QSSB_SYS(setgid),
QSSB_SYS(chroot),
QSSB_SYS(pivot_root),
QSSB_SYS(mount),
QSSB_SYS(setns),
QSSB_SYS(unshare),
QSSB_SYS(ptrace),
QSSB_SYS(personality),
QSSB_SYS(execve),
-1
};
struct qssb_path_policy
{
const char *mountpoint;
int policy;
struct qssb_path_policy *next;
};
/* Policy tells qssb what to do */
struct qssb_policy
{
int drop_caps;
int preserve_cwd;
int not_dumpable;
int no_new_privs;
int namespace_options;
int syscall_default_policy;
int *blacklisted_syscalls;
int *allowed_syscalls;
char chroot_target_path[PATH_MAX];
const char *chdir_path;
struct qssb_path_policy *path_policies;
};
/* Creates the default policy
* Must be freed using qssb_free_policy
* @returns: default policy */
struct qssb_policy *qssb_init_policy()
{
struct qssb_policy *result = (struct qssb_policy *) calloc(1, sizeof(struct qssb_policy));
result->blacklisted_syscalls = default_blacklisted_syscals;
result->drop_caps = 1;
result->not_dumpable = 1;
result->no_new_privs = 1;
result->namespace_options = QSSB_UNSHARE_MOUNT | QSSB_UNSHARE_USER;
result->chdir_path = NULL;
result->chroot_target_path[0] = '\0';
result->path_policies = NULL;
return result;
}
/*
* Fills buffer with random characters a-z.
* The string will be null terminated.
*
* @returns: number of written chars (excluding terminating null byte) on success
*/
int random_string(char *buffer, size_t buffer_length)
{
int r = getrandom(buffer, buffer_length-1, GRND_NONBLOCK);
if(r != -1 && (size_t) r == buffer_length-1)
{
int i = 0;
while(i < r)
{
buffer[i] = 'a' + ((unsigned int)buffer[i] % 26);
++i;
}
buffer[buffer_length-1] = '\0';
return i;
}
return 0;
}
/* Creates a directory and all necessary parent directories
*
* @returns: 0 on success, -ERRNO on failure
* */
static int mkdir_structure(const char *p, mode_t mode)
{
char path[PATH_MAX] = { 0 };
int res = snprintf(path, sizeof(path), "%s/", p);
if(res < 0)
{
QSSB_LOG_ERROR("qssb: mkdir_strucutre: error during path concatination\n");
return -EINVAL;
}
if(res >= PATH_MAX)
{
QSSB_LOG_ERROR("qssb: mkdir_structure: path concatination truncated\n");
return -EINVAL;
}
char *begin = path;
char *end = begin+1;
while(*end)
{
if(*end == '/')
{
*end = 0;
if(mkdir(begin, mode) < 0)
{
if(errno == EEXIST)
{
//TODO: stat, test if it is a directory, if not, err
}
else
{
QSSB_LOG_ERROR("Failed to create directory for chroot: %s\n", begin);
return -1;
}
}
*end = '/';
++end;
while(*end == '/')
{
++end;
}
}
else
{
++end;
}
}
return 0;
}
/* @returns: argument for mount(2) flags */
static int get_policy_mount_flags(struct qssb_path_policy *policy)
{
int result = 0;
if( (policy->policy & QSSB_MOUNT_ALLOW_DEV) == 0)
{
result |= MS_NODEV;
}
if( (policy->policy & QSSB_MOUNT_ALLOW_EXEC) == 0)
{
result |= MS_NOEXEC;
}
if( (policy->policy & QSSB_MOUNT_ALLOW_SETUID) == 0)
{
result |= MS_NOSUID;
}
if( ((policy->policy) & (QSSB_MOUNT_ALLOW_WRITE)) == QSSB_MOUNT_ALLOW_READ)
{
result |= MS_RDONLY;
}
if( !(policy->policy & QSSB_MOUNT_NOT_REC))
{
result |= MS_REC;
}
return result;
}
/* Helper to mount directories into the chroot path "chroot_target_path"
* Paths will be created if necessary
* @returns: 0 on sucess, -ERRNO on failure */
static int mount_to_chroot(const char *chroot_target_path, struct qssb_path_policy *path_policy)
{
while(path_policy != NULL)
{
char path_inside_chroot[PATH_MAX];
int written = snprintf(path_inside_chroot, sizeof(path_inside_chroot), "%s/%s", chroot_target_path, path_policy->mountpoint);
if(written < 0)
{
QSSB_LOG_ERROR("qssb: mount_to_chroot: Error during path concatination\n");
return -EINVAL;
}
if(written >= PATH_MAX)
{
QSSB_LOG_ERROR("qssb: mount_to_chroot: path concatination truncated\n");
return -EINVAL;
}
int ret = mkdir_structure(path_inside_chroot, 0700);
if(ret < 0)
{
QSSB_LOG_ERROR("Error creating directory structure while mounting paths to chroot. %s\n", strerror(errno));
return ret;
}
int mount_flags = get_policy_mount_flags(path_policy);
//all we do is bind mounts
mount_flags |= MS_BIND;
if(path_policy->policy & QSSB_MOUNT_ALLOW_READ)
{
ret = mount(path_policy->mountpoint, path_inside_chroot, NULL, mount_flags, NULL);
if(ret < 0 )
{
QSSB_LOG_ERROR("Error: Failed to mount %s to %s: %s\n", path_policy->mountpoint, path_inside_chroot, strerror(errno));
return ret;
}
//remount so noexec, readonly etc. take effect
ret = mount(NULL, path_inside_chroot, NULL, mount_flags | MS_REMOUNT, NULL);
if(ret < 0 )
{
QSSB_LOG_ERROR("Error: Failed to remount %s: %s", path_inside_chroot, strerror(errno));
return ret;
}
}
path_policy = path_policy->next;
}
return 0;
}
/* Ends the policy as best as possible. */
/* TODO: can this function do actually anything useful?*/
int qssb_end_policy(struct qssb_policy *ctxt)
{
return 0;
}
/*
* Frees the memory taken by a qssb_policy object
*/
void qssb_free_policy(struct qssb_policy *ctxt)
{
free(ctxt);
}
/* Enters the specified namespaces */
static int enter_namespaces(int namespace_options)
{
if(namespace_options & QSSB_UNSHARE_USER)
{
int ret = unshare(CLONE_NEWUSER);
if(ret == -1)
{
QSSB_LOG_ERROR("Error: Failed to unshare user namespaces: %s\n", strerror(errno));
return ret;
}
uid_t current_uid = getuid();
gid_t current_gid = getgid();
//TODO: check errors
FILE *fp = fopen("/proc/self/setgroups", "w");
fprintf(fp, "deny");
fclose(fp);
fp = fopen("/proc/self/uid_map", "w");
fprintf(fp, "0 %i", current_uid);
fclose(fp);
fp = fopen("/proc/self/gid_map", "w");
fprintf(fp, "0 %i", current_gid);
fclose(fp);
}
if(namespace_options & QSSB_UNSHARE_MOUNT)
{
int ret = unshare(CLONE_NEWNS);
if(ret == -1)
{
QSSB_LOG_ERROR("Error: Failed to unshare mount namespaces: %s\n", strerror(errno));
return ret;
}
}
if(namespace_options & QSSB_UNSHARE_NETWORK)
{
int ret = unshare(CLONE_NEWNET);
if(ret == -1)
{
QSSB_LOG_ERROR("Error: Failed to unshare network namespace: %s\n", strerror(errno));
return ret;
}
}
return 0;
}
/* Drops all capabiltiies held by the process
*
* @returns: 0 on sucess, -1 on error
*/
static int drop_caps()
{
int cap = 0;
int res = 0;
while((res = prctl(PR_CAPBSET_DROP, cap, 0, 0, 0)) == 0)
{
++cap;
}
if(res == -1 && errno != EINVAL)
{
QSSB_LOG_ERROR("Failed to drop the capability bounding set!");
return -errno;
}
//TODO: systems that are not 64 bit
struct __user_cap_header_struct h = { 0 };
h.pid = 0;
h.version = _LINUX_CAPABILITY_VERSION_3;
struct __user_cap_data_struct drop[2];
drop[0].effective = 0;
drop[0].permitted = 0;
drop[0].inheritable = 0;
drop[1].effective = 0;
drop[1].permitted = 0;
drop[1].inheritable = 0;
if(capset(&h, drop) == -1)
{
QSSB_LOG_ERROR("Failed to drop capabilities: %s\n", strerror(errno));;
return -errno;
}
return 0;
}
/*
* Enables the per_syscall seccomp action for system calls
*
* syscalls: array of system calls numbers. -1 must be the last entry.
* per_syscall: action to apply for each system call
* default_action: the default action at the end
*
* @returns: 0 on success, -1 on error
*/
static int seccomp_enable(int *syscalls, int per_syscall, int default_action)
{
struct sock_filter filter[1024] =
{
LOAD_SYSCALL_NR,
};
unsigned short int current_filter_index = 1;
while(*syscalls >= 0)
{
unsigned int sysc = (unsigned int) *syscalls;
struct sock_filter syscall = BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, sysc, 0, 1);
struct sock_filter action = BPF_STMT(BPF_RET+BPF_K, per_syscall);
filter[current_filter_index++] = syscall;
filter[current_filter_index++] = action;
++syscalls;
}
struct sock_filter da = BPF_STMT(BPF_RET+BPF_K, default_action);
filter[current_filter_index] = da;
++current_filter_index;
struct sock_fprog prog = {
.len = current_filter_index ,
.filter = filter,
};
if (prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &prog) == -1)
{
QSSB_LOG_ERROR("prctl SET_SECCOMP %s\n", strerror(errno));
return -1;
}
return 0;
}
/*
* Blacklists the specified systemcalls.
*
* syscalls: array of system calls numbers. -1 must be the last entry.
*/
static int seccomp_enable_blacklist(int *syscalls)
{
return seccomp_enable(syscalls, SECCOMP_RET_KILL, SECCOMP_RET_ALLOW);
}
/*
* Blacklists the specified systemcalls.
*
* syscalls: array of system calls numbers. -1 must be the last entry.
*/
static int seccomp_enable_whitelist(int *syscalls)
{
return seccomp_enable(syscalls, SECCOMP_RET_ALLOW, SECCOMP_RET_KILL);
}
/* Enables the specified qssb_policy.
*
* The calling process is supposed *TO BE WRITTEN* if
* this function fails.
* @returns: 0 on sucess, <0 on error
*/
int qssb_enable_policy(struct qssb_policy *policy)
{
if(policy->blacklisted_syscalls != NULL && policy->allowed_syscalls != NULL)
{
QSSB_LOG_ERROR("Error: Cannot mix blacklisted and whitelisted systemcalls\n");
return -EINVAL;
}
if(enter_namespaces(policy->namespace_options) < 0)
{
QSSB_LOG_ERROR("Error while trying to enter namespaces\n");
return -1;
}
if(policy->path_policies != NULL)
{
if(*policy->chroot_target_path == '\0')
{
char random_str[17];
if(random_string(random_str, sizeof(random_str)) == 16)
{
int res = snprintf(policy->chroot_target_path, sizeof(policy->chroot_target_path), "%s/.sandbox_%" PRIdMAX "_%s", QSSB_TEMP_DIR, (intmax_t)getpid(), random_str);
if(res < 0)
{
QSSB_LOG_ERROR("qssb: qssb_enable_policy: error during path concatination\n");
return -EINVAL;
}
if(res >= PATH_MAX)
{
QSSB_LOG_ERROR("qssb: qssb_enable_policy: path concatination truncated\n");
return -EINVAL;
}
}
else
{
QSSB_LOG_ERROR("Error creating random sandbox directory name\n");
return -1;
}
}
if(mount_to_chroot(policy->chroot_target_path, policy->path_policies) < 0)
{
QSSB_LOG_ERROR("mount_to_chroot: setup of path policies failed\n");
return -1;
}
if(chroot(policy->chroot_target_path) < 0)
{
QSSB_LOG_ERROR("chroot: failed to enter %s\n", policy->chroot_target_path);
return -1;
}
if(policy->chdir_path == NULL)
{
policy->chdir_path = "/";
}
}
if(policy->chdir_path != NULL && chdir(policy->chdir_path) < 0)
{
QSSB_LOG_ERROR("chdir to %s failed\n", policy->chdir_path);
return -1;
}
if(policy->drop_caps)
{
if(drop_caps() < 0)
{
QSSB_LOG_ERROR("failed to drop capabilities\n");
return -1;
}
}
if(policy->not_dumpable)
{
if(prctl(PR_SET_DUMPABLE, 0) == -1)
{
QSSB_LOG_ERROR("prctl: PR_SET_DUMPABLE failed\n");
return -1;
}
}
if(policy->no_new_privs)
{
if(prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) == -1)
{
QSSB_LOG_ERROR("prctl: PR_SET_NO_NEW_PRIVS failed: %s\n", strerror(errno));
return -1;
}
}
if(policy->allowed_syscalls != NULL)
{
if(seccomp_enable_whitelist(policy->allowed_syscalls) <0)
{
QSSB_LOG_ERROR("seccomp_enable_whitelist failed\n");
return -1;
}
}
if(policy->blacklisted_syscalls != NULL)
{
if(seccomp_enable_blacklist(policy->blacklisted_syscalls) <0)
{
QSSB_LOG_ERROR("seccomp_enable_blacklist failed\n");
return -1;
}
}
return 0;
}
#endif