I have implemented libseccomp restrict certain system calls for a process. It is the first program that I have written. However, when I debugged it using strace, it appears that libseccomp is not functioning as expected.
Following is libseccomp code:
#include <stdio.h>
#include <seccomp.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>
#include "../runner.h"
// Function to apply seccomp rules
int python_seccomp_rules(struct config *_config)
{
// Syscalls blacklist array
int syscalls_blacklist[] = {
SCMP_SYS(fork), SCMP_SYS(vfork), SCMP_SYS(kill)
};
// Initializing seccomp context
scmp_filter_ctx ctx = seccomp_init(SCMP_ACT_ALLOW);
if (!ctx)
{
return LOAD_SECCOMP_FAILED;
}
// Blacklist specified syscalls
int syscalls_blacklist_length = sizeof(syscalls_blacklist) / sizeof(int);
for (int i = 0; i < syscalls_blacklist_length; i++)
{
if (seccomp_rule_add(ctx, SCMP_ACT_KILL, syscalls_blacklist[i], 0) != 0)
{
seccomp_release(ctx);
return LOAD_SECCOMP_FAILED;
}
}
// Deny socket calls, python will be killed immediately
if (seccomp_rule_add(ctx, SCMP_ACT_ERRNO(EACCES), SCMP_SYS(socket), 0) != 0)
{
seccomp_release(ctx);
return LOAD_SECCOMP_FAILED;
}
// Add extra rule for execve
if (seccomp_rule_add(ctx, SCMP_ACT_KILL, SCMP_SYS(execve), 1, SCMP_A0(SCMP_CMP_NE, (scmp_datum_t)(_config->exe_path))) != 0)
{
seccomp_release(ctx);
return LOAD_SECCOMP_FAILED;
}
// Deny "w" and "rw" modes using open
if (seccomp_rule_add(ctx, SCMP_ACT_KILL, SCMP_SYS(open), 1, SCMP_CMP(1, SCMP_CMP_MASKED_EQ, O_WRONLY, O_WRONLY)) != 0)
{
seccomp_release(ctx);
return LOAD_SECCOMP_FAILED;
}
if (seccomp_rule_add(ctx, SCMP_ACT_KILL, SCMP_SYS(open), 1, SCMP_CMP(1, SCMP_CMP_MASKED_EQ, O_RDWR, O_RDWR)) != 0)
{
seccomp_release(ctx);
return LOAD_SECCOMP_FAILED;
}
// Deny "w" and "rw" modes using openat
if (seccomp_rule_add(ctx, SCMP_ACT_KILL, SCMP_SYS(openat), 1, SCMP_CMP(2, SCMP_CMP_MASKED_EQ, O_WRONLY, O_WRONLY)) != 0)
{
seccomp_release(ctx);
return LOAD_SECCOMP_FAILED;
}
if (seccomp_rule_add(ctx, SCMP_ACT_KILL, SCMP_SYS(openat), 1, SCMP_CMP(2, SCMP_CMP_MASKED_EQ, O_RDWR, O_RDWR)) != 0)
{
When I traced it using strace command, I got the following output:
6885 15:57:14 seccomp(SECCOMP_SET_MODE_STRICT, 0x1, NULL) = -1 EINVAL (Invalid argument)
6885 15:57:14 seccomp(SECCOMP_SET_MODE_FILTER, SECCOMP_FILTER_FLAG_TSYNC, NULL) = -1 EFAULT (Bad address)
6885 15:57:14 seccomp(SECCOMP_SET_MODE_FILTER, SECCOMP_FILTER_FLAG_LOG, NULL) = -1 EFAULT (Bad address)
6885 15:57:14 seccomp(SECCOMP_GET_ACTION_AVAIL, 0, [SECCOMP_RET_LOG]) = 0
6885 15:57:14 seccomp(SECCOMP_GET_ACTION_AVAIL, 0, [SECCOMP_RET_KILL_PROCESS]) = 0
6885 15:57:14 seccomp(SECCOMP_SET_MODE_FILTER, SECCOMP_FILTER_FLAG_SPEC_ALLOW, NULL) = -1 EFAULT (Bad address)
6885 15:57:14 seccomp(SECCOMP_SET_MODE_FILTER, SECCOMP_FILTER_FLAG_NEW_LISTENER, NULL) = -1 EFAULT (Bad address)
6885 15:57:14 seccomp(SECCOMP_GET_NOTIF_SIZES, 0, {seccomp_notif=80, seccomp_notif_resp=24, seccomp_data=64}) = 0
6885 15:57:14 seccomp(SECCOMP_SET_MODE_FILTER, SECCOMP_FILTER_FLAG_TSYNC_ESRCH, NULL) = -1 EFAULT (Bad address)
6885 15:57:14 prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) = 0
6885 15:57:14 seccomp(SECCOMP_SET_MODE_FILTER, 0, {len=30, filter=0x55a7aaa8b490}) = 0
Thanks in advance!