cregit-Linux how code gets into the kernel

Release 4.10 samples/seccomp/bpf-fancy.c

Directory: samples/seccomp
 * Seccomp BPF example using a macro-based generator.
 * Copyright (c) 2012 The Chromium OS Authors <>
 * Author: Will Drewry <>
 * The code may be used by anyone for any purpose,
 * and can serve as a starting point for developing
 * applications using prctl(PR_ATTACH_SECCOMP_FILTER).

#include <linux/filter.h>
#include <linux/seccomp.h>
#include <linux/unistd.h>
#include <stdio.h>
#include <string.h>
#include <sys/prctl.h>
#include <unistd.h>

#include "bpf-helper.h"


#define PR_SET_NO_NEW_PRIVS 38

int main(int argc, char **argv) { struct bpf_labels l = { .count = 0, }; static const char msg1[] = "Please type something: "; static const char msg2[] = "You typed: "; char buf[256]; struct sock_filter filter[] = { /* TODO: LOAD_SYSCALL_NR(arch) and enforce an arch */ LOAD_SYSCALL_NR, SYSCALL(__NR_exit, ALLOW), SYSCALL(__NR_exit_group, ALLOW), SYSCALL(__NR_write, JUMP(&l, write_fd)), SYSCALL(__NR_read, JUMP(&l, read)), DENY, /* Don't passthrough into a label */ LABEL(&l, read), ARG(0), JNE(STDIN_FILENO, DENY), ARG(1), JNE((unsigned long)buf, DENY), ARG(2), JGE(sizeof(buf), DENY), ALLOW, LABEL(&l, write_fd), ARG(0), JEQ(STDOUT_FILENO, JUMP(&l, write_buf)), JEQ(STDERR_FILENO, JUMP(&l, write_buf)), DENY, LABEL(&l, write_buf), ARG(1), JEQ((unsigned long)msg1, JUMP(&l, msg1_len)), JEQ((unsigned long)msg2, JUMP(&l, msg2_len)), JEQ((unsigned long)buf, JUMP(&l, buf_len)), DENY, LABEL(&l, msg1_len), ARG(2), JLT(sizeof(msg1), ALLOW), DENY, LABEL(&l, msg2_len), ARG(2), JLT(sizeof(msg2), ALLOW), DENY, LABEL(&l, buf_len), ARG(2), JLT(sizeof(buf), ALLOW), DENY, }; struct sock_fprog prog = { .filter = filter, .len = (unsigned short)(sizeof(filter)/sizeof(filter[0])), }; ssize_t bytes; bpf_resolve_jumps(&l, filter, sizeof(filter)/sizeof(*filter)); if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) { perror("prctl(NO_NEW_PRIVS)"); return 1; } if (prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &prog)) { perror("prctl(SECCOMP)"); return 1; } syscall(__NR_write, STDOUT_FILENO, msg1, strlen(msg1)); bytes = syscall(__NR_read, STDIN_FILENO, buf, sizeof(buf)-1); bytes = (bytes > 0 ? bytes : 0); syscall(__NR_write, STDERR_FILENO, msg2, strlen(msg2)); syscall(__NR_write, STDERR_FILENO, buf, bytes); /* Now get killed */ syscall(__NR_write, STDERR_FILENO, msg2, strlen(msg2)+2); return 0; }


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Directory: samples/seccomp
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