| 1 | |
| 2 | |
| 3 | * Naive system call dropper built on seccomp_filter.
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| 4 | *
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| 5 | * Copyright (c) 2012 The Chromium OS Authors <[email protected]>
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| 6 | * Author: Will Drewry <[email protected]>
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| 7 | *
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| 8 | * The code may be used by anyone for any purpose,
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| 9 | * and can serve as a starting point for developing
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| 10 | * applications using prctl(PR_SET_SECCOMP, 2, ...).
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| 11 | *
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| 12 | * When run, returns the specified errno for the specified
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| 13 | * system call number against the given architecture.
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| 14 | *
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| 15 |
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| 16 |
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| 17 | #include <errno.h>
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| 18 | #include <linux/audit.h>
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| 19 | #include <linux/filter.h>
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| 20 | #include <linux/seccomp.h>
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| 21 | #include <linux/unistd.h>
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| 22 | #include <stdio.h>
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| 23 | #include <stddef.h>
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| 24 | #include <stdlib.h>
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| 25 | #include <sys/prctl.h>
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| 26 | #include <unistd.h>
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| 27 |
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| 28 | static int install_filter(int arch, int nr, int error)
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| 29 | {
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| 30 | struct sock_filter filter[] = {
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| 31 | BPF_STMT(BPF_LD+BPF_W+BPF_ABS,
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| 32 | (offsetof(struct seccomp_data, arch))),
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| 33 | BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, arch, 0, 3),
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| 34 | BPF_STMT(BPF_LD+BPF_W+BPF_ABS,
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| 35 | (offsetof(struct seccomp_data, nr))),
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| 36 | BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, nr, 0, 1),
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| 37 | BPF_STMT(BPF_RET+BPF_K,
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| 38 | SECCOMP_RET_ERRNO|(error & SECCOMP_RET_DATA)),
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| 39 | BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW),
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| 40 | };
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| 41 | struct sock_fprog prog = {
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| 42 | .len = (unsigned short)(sizeof(filter)/sizeof(filter[0])),
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| 43 | .filter = filter,
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| 44 | };
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| 45 | if (error == -1) {
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| 46 | struct sock_filter kill = BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_KILL);
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| 47 | filter[4] = kill;
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| 48 | }
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| 49 | if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
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| 50 | perror("prctl(NO_NEW_PRIVS)");
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| 51 | return 1;
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| 52 | }
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| 53 | if (prctl(PR_SET_SECCOMP, 2, &prog)) {
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| 54 | perror("prctl(PR_SET_SECCOMP)");
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| 55 | return 1;
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| 56 | }
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| 57 | return 0;
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| 58 | }
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| 59 |
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| 60 | int main(int argc, char **argv)
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| 61 | {
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| 62 | if (argc < 5) {
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| 63 | fprintf(stderr, "Usage:\n"
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| 64 | "dropper <arch> <syscall_nr> <errno> <prog> [<args>]\n"
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| 65 | "Hint: AUDIT_ARCH_I386: 0x%X\n"
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| 66 | " AUDIT_ARCH_X86_64: 0x%X\n"
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| 67 | " errno == -1 means SECCOMP_RET_KILL\n"
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| 68 | "\n", AUDIT_ARCH_I386, AUDIT_ARCH_X86_64);
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| 69 | return 1;
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| 70 | }
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| 71 | if (install_filter(strtol(argv[1], NULL, 0), strtol(argv[2], NULL, 0),
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| 72 | strtol(argv[3], NULL, 0)))
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| 73 | return 1;
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| 74 | execv(argv[4], &argv[4]);
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| 75 | printf("Failed to execv\n");
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| 76 | return 255;
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| 77 | }
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