#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <linux/seccomp.h>
#include <sys/prctl.h>
//From https://sysdig.com/blog/selinux-seccomp-falco-technical-discussion/
//gcc seccomp_strict.c -o seccomp_strict
int main(int argc, char **argv)
{
int output = open("output.txt", O_WRONLY);
const char *val = "test";
//enables strict seccomp mode
printf("Calling prctl() to set seccomp strict mode...\n");
prctl(PR_SET_SECCOMP, SECCOMP_MODE_STRICT);
//This is allowed as the file was already opened
printf("Writing to an already open file...\n");
write(output, val, strlen(val)+1);
//This isn't allowed
printf("Trying to open file for reading...\n");
int input = open("output.txt", O_RDONLY);
printf("You will not see this message--the process will be killed first\n");
}
Seccomp-bpf
这种模式允许使用使用伯克利数据包过滤器规则实现的可配置策略来过滤系统调用。
seccomp_bpf.c
#include <seccomp.h>
#include <unistd.h>
#include <stdio.h>
#include <errno.h>
//https://security.stackexchange.com/questions/168452/how-is-sandboxing-implemented/175373
//gcc seccomp_bpf.c -o seccomp_bpf -lseccomp
void main(void) {
/* initialize the libseccomp context */
scmp_filter_ctx ctx = seccomp_init(SCMP_ACT_KILL);
/* allow exiting */
printf("Adding rule : Allow exit_group\n");
seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(exit_group), 0);
/* allow getting the current pid */
//printf("Adding rule : Allow getpid\n");
//seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(getpid), 0);
printf("Adding rule : Deny getpid\n");
seccomp_rule_add(ctx, SCMP_ACT_ERRNO(EBADF), SCMP_SYS(getpid), 0);
/* allow changing data segment size, as required by glibc */
printf("Adding rule : Allow brk\n");
seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(brk), 0);
/* allow writing up to 512 bytes to fd 1 */
printf("Adding rule : Allow write upto 512 bytes to FD 1\n");
seccomp_rule_add(ctx, SCMP_ACT_ALLOW, SCMP_SYS(write), 2,
SCMP_A0(SCMP_CMP_EQ, 1),
SCMP_A2(SCMP_CMP_LE, 512));
/* if writing to any other fd, return -EBADF */
printf("Adding rule : Deny write to any FD except 1 \n");
seccomp_rule_add(ctx, SCMP_ACT_ERRNO(EBADF), SCMP_SYS(write), 1,
SCMP_A0(SCMP_CMP_NE, 1));
/* load and enforce the filters */
printf("Load rules and enforce \n");
seccomp_load(ctx);
seccomp_release(ctx);
//Get the getpid is denied, a weird number will be returned like
//this process is -9
printf("this process is %d\n", getpid());
}