78 lines
2.1 KiB
C
78 lines
2.1 KiB
C
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// SPDX-License-Identifier: GPL-2.0
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/*
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* Naive system call dropper built on seccomp_filter.
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*
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* Copyright (c) 2012 The Chromium OS Authors <chromium-os-dev@chromium.org>
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* Author: Will Drewry <wad@chromium.org>
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*
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* The code may be used by anyone for any purpose,
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* and can serve as a starting point for developing
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* applications using prctl(PR_SET_SECCOMP, 2, ...).
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*
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* When run, returns the specified errno for the specified
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* system call number against the given architecture.
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*
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*/
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#include <errno.h>
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#include <linux/audit.h>
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#include <linux/filter.h>
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#include <linux/seccomp.h>
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#include <linux/unistd.h>
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#include <stdio.h>
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#include <stddef.h>
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#include <stdlib.h>
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#include <sys/prctl.h>
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#include <unistd.h>
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static int install_filter(int arch, int nr, int error)
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{
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struct sock_filter filter[] = {
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BPF_STMT(BPF_LD+BPF_W+BPF_ABS,
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(offsetof(struct seccomp_data, arch))),
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BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, arch, 0, 3),
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BPF_STMT(BPF_LD+BPF_W+BPF_ABS,
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(offsetof(struct seccomp_data, nr))),
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BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, nr, 0, 1),
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BPF_STMT(BPF_RET+BPF_K,
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SECCOMP_RET_ERRNO|(error & SECCOMP_RET_DATA)),
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BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW),
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};
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struct sock_fprog prog = {
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.len = (unsigned short)(sizeof(filter)/sizeof(filter[0])),
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.filter = filter,
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};
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if (error == -1) {
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struct sock_filter kill = BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_KILL);
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filter[4] = kill;
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}
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if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
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perror("prctl(NO_NEW_PRIVS)");
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return 1;
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}
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if (prctl(PR_SET_SECCOMP, 2, &prog)) {
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perror("prctl(PR_SET_SECCOMP)");
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return 1;
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}
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return 0;
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}
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int main(int argc, char **argv)
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{
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if (argc < 5) {
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fprintf(stderr, "Usage:\n"
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"dropper <arch> <syscall_nr> <errno> <prog> [<args>]\n"
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"Hint: AUDIT_ARCH_I386: 0x%X\n"
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" AUDIT_ARCH_X86_64: 0x%X\n"
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" errno == -1 means SECCOMP_RET_KILL\n"
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"\n", AUDIT_ARCH_I386, AUDIT_ARCH_X86_64);
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return 1;
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}
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if (install_filter(strtol(argv[1], NULL, 0), strtol(argv[2], NULL, 0),
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strtol(argv[3], NULL, 0)))
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return 1;
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execv(argv[4], &argv[4]);
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printf("Failed to execv\n");
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return 255;
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}
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