diff options
Diffstat (limited to 'samples/seccomp')
| -rw-r--r-- | samples/seccomp/.gitignore | 3 | ||||
| -rw-r--r-- | samples/seccomp/Makefile | 48 | ||||
| -rw-r--r-- | samples/seccomp/bpf-direct.c | 190 | ||||
| -rw-r--r-- | samples/seccomp/bpf-fancy.c | 104 | ||||
| -rw-r--r-- | samples/seccomp/bpf-helper.c | 95 | ||||
| -rw-r--r-- | samples/seccomp/bpf-helper.h | 243 | ||||
| -rw-r--r-- | samples/seccomp/dropper.c | 68 |
7 files changed, 751 insertions, 0 deletions
diff --git a/samples/seccomp/.gitignore b/samples/seccomp/.gitignore new file mode 100644 index 000000000..78fb78184 --- /dev/null +++ b/samples/seccomp/.gitignore @@ -0,0 +1,3 @@ +bpf-direct +bpf-fancy +dropper diff --git a/samples/seccomp/Makefile b/samples/seccomp/Makefile new file mode 100644 index 000000000..1b4e4b8f5 --- /dev/null +++ b/samples/seccomp/Makefile @@ -0,0 +1,48 @@ +# kbuild trick to avoid linker error. Can be omitted if a module is built. +obj- := dummy.o + +hostprogs-$(CONFIG_SECCOMP_FILTER) := bpf-fancy dropper bpf-direct + +HOSTCFLAGS_bpf-fancy.o += -I$(objtree)/usr/include +HOSTCFLAGS_bpf-fancy.o += -idirafter $(objtree)/include +HOSTCFLAGS_bpf-helper.o += -I$(objtree)/usr/include +HOSTCFLAGS_bpf-helper.o += -idirafter $(objtree)/include +bpf-fancy-objs := bpf-fancy.o bpf-helper.o + +HOSTCFLAGS_dropper.o += -I$(objtree)/usr/include +HOSTCFLAGS_dropper.o += -idirafter $(objtree)/include +dropper-objs := dropper.o + +HOSTCFLAGS_bpf-direct.o += -I$(objtree)/usr/include +HOSTCFLAGS_bpf-direct.o += -idirafter $(objtree)/include +bpf-direct-objs := bpf-direct.o + +# Try to match the kernel target. +ifndef CROSS_COMPILE +ifndef CONFIG_64BIT + +# s390 has -m31 flag to build 31 bit binaries +ifndef CONFIG_S390 +MFLAG = -m32 +else +MFLAG = -m31 +endif + +HOSTCFLAGS_bpf-direct.o += $(MFLAG) +HOSTCFLAGS_dropper.o += $(MFLAG) +HOSTCFLAGS_bpf-helper.o += $(MFLAG) +HOSTCFLAGS_bpf-fancy.o += $(MFLAG) +HOSTLOADLIBES_bpf-direct += $(MFLAG) +HOSTLOADLIBES_bpf-fancy += $(MFLAG) +HOSTLOADLIBES_dropper += $(MFLAG) +endif +always := $(hostprogs-y) +else +# MIPS system calls are defined based on the -mabi that is passed +# to the toolchain which may or may not be a valid option +# for the host toolchain. So disable tests if target architecture +# is MIPS but the host isn't. +ifndef CONFIG_MIPS +always := $(hostprogs-y) +endif +endif diff --git a/samples/seccomp/bpf-direct.c b/samples/seccomp/bpf-direct.c new file mode 100644 index 000000000..151ec3f52 --- /dev/null +++ b/samples/seccomp/bpf-direct.c @@ -0,0 +1,190 @@ +/* + * Seccomp filter example for x86 (32-bit and 64-bit) with BPF macros + * + * Copyright (c) 2012 The Chromium OS Authors <chromium-os-dev@chromium.org> + * Author: Will Drewry <wad@chromium.org> + * + * The code may be used by anyone for any purpose, + * and can serve as a starting point for developing + * applications using prctl(PR_SET_SECCOMP, 2, ...). + */ +#if defined(__i386__) || defined(__x86_64__) +#define SUPPORTED_ARCH 1 +#endif + +#if defined(SUPPORTED_ARCH) +#define __USE_GNU 1 +#define _GNU_SOURCE 1 + +#include <linux/types.h> +#include <linux/filter.h> +#include <linux/seccomp.h> +#include <linux/unistd.h> +#include <signal.h> +#include <stdio.h> +#include <stddef.h> +#include <string.h> +#include <sys/prctl.h> +#include <unistd.h> + +#define syscall_arg(_n) (offsetof(struct seccomp_data, args[_n])) +#define syscall_nr (offsetof(struct seccomp_data, nr)) + +#if defined(__i386__) +#define REG_RESULT REG_EAX +#define REG_SYSCALL REG_EAX +#define REG_ARG0 REG_EBX +#define REG_ARG1 REG_ECX +#define REG_ARG2 REG_EDX +#define REG_ARG3 REG_ESI +#define REG_ARG4 REG_EDI +#define REG_ARG5 REG_EBP +#elif defined(__x86_64__) +#define REG_RESULT REG_RAX +#define REG_SYSCALL REG_RAX +#define REG_ARG0 REG_RDI +#define REG_ARG1 REG_RSI +#define REG_ARG2 REG_RDX +#define REG_ARG3 REG_R10 +#define REG_ARG4 REG_R8 +#define REG_ARG5 REG_R9 +#endif + +#ifndef PR_SET_NO_NEW_PRIVS +#define PR_SET_NO_NEW_PRIVS 38 +#endif + +#ifndef SYS_SECCOMP +#define SYS_SECCOMP 1 +#endif + +static void emulator(int nr, siginfo_t *info, void *void_context) +{ + ucontext_t *ctx = (ucontext_t *)(void_context); + int syscall; + char *buf; + ssize_t bytes; + size_t len; + if (info->si_code != SYS_SECCOMP) + return; + if (!ctx) + return; + syscall = ctx->uc_mcontext.gregs[REG_SYSCALL]; + buf = (char *) ctx->uc_mcontext.gregs[REG_ARG1]; + len = (size_t) ctx->uc_mcontext.gregs[REG_ARG2]; + + if (syscall != __NR_write) + return; + if (ctx->uc_mcontext.gregs[REG_ARG0] != STDERR_FILENO) + return; + /* Redirect stderr messages to stdout. Doesn't handle EINTR, etc */ + ctx->uc_mcontext.gregs[REG_RESULT] = -1; + if (write(STDOUT_FILENO, "[ERR] ", 6) > 0) { + bytes = write(STDOUT_FILENO, buf, len); + ctx->uc_mcontext.gregs[REG_RESULT] = bytes; + } + return; +} + +static int install_emulator(void) +{ + struct sigaction act; + sigset_t mask; + memset(&act, 0, sizeof(act)); + sigemptyset(&mask); + sigaddset(&mask, SIGSYS); + + act.sa_sigaction = &emulator; + act.sa_flags = SA_SIGINFO; + if (sigaction(SIGSYS, &act, NULL) < 0) { + perror("sigaction"); + return -1; + } + if (sigprocmask(SIG_UNBLOCK, &mask, NULL)) { + perror("sigprocmask"); + return -1; + } + return 0; +} + +static int install_filter(void) +{ + struct sock_filter filter[] = { + /* Grab the system call number */ + BPF_STMT(BPF_LD+BPF_W+BPF_ABS, syscall_nr), + /* Jump table for the allowed syscalls */ + BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_rt_sigreturn, 0, 1), + BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW), +#ifdef __NR_sigreturn + BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_sigreturn, 0, 1), + BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW), +#endif + BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_exit_group, 0, 1), + BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW), + BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_exit, 0, 1), + BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW), + BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_read, 1, 0), + BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_write, 3, 2), + + /* Check that read is only using stdin. */ + BPF_STMT(BPF_LD+BPF_W+BPF_ABS, syscall_arg(0)), + BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, STDIN_FILENO, 4, 0), + BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_KILL), + + /* Check that write is only using stdout */ + BPF_STMT(BPF_LD+BPF_W+BPF_ABS, syscall_arg(0)), + BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, STDOUT_FILENO, 1, 0), + /* Trap attempts to write to stderr */ + BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, STDERR_FILENO, 1, 2), + + BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW), + BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_TRAP), + BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_KILL), + }; + struct sock_fprog prog = { + .len = (unsigned short)(sizeof(filter)/sizeof(filter[0])), + .filter = 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"); + return 1; + } + return 0; +} + +#define payload(_c) (_c), sizeof((_c)) +int main(int argc, char **argv) +{ + char buf[4096]; + ssize_t bytes = 0; + if (install_emulator()) + return 1; + if (install_filter()) + return 1; + syscall(__NR_write, STDOUT_FILENO, + payload("OHAI! WHAT IS YOUR NAME? ")); + bytes = syscall(__NR_read, STDIN_FILENO, buf, sizeof(buf)); + syscall(__NR_write, STDOUT_FILENO, payload("HELLO, ")); + syscall(__NR_write, STDOUT_FILENO, buf, bytes); + syscall(__NR_write, STDERR_FILENO, + payload("Error message going to STDERR\n")); + return 0; +} +#else /* SUPPORTED_ARCH */ +/* + * This sample is x86-only. Since kernel samples are compiled with the + * host toolchain, a non-x86 host will result in using only the main() + * below. + */ +int main(void) +{ + return 1; +} +#endif /* SUPPORTED_ARCH */ diff --git a/samples/seccomp/bpf-fancy.c b/samples/seccomp/bpf-fancy.c new file mode 100644 index 000000000..e8b24f443 --- /dev/null +++ b/samples/seccomp/bpf-fancy.c @@ -0,0 +1,104 @@ +/* + * Seccomp BPF example using a macro-based generator. + * + * Copyright (c) 2012 The Chromium OS Authors <chromium-os-dev@chromium.org> + * Author: Will Drewry <wad@chromium.org> + * + * 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" + +#ifndef PR_SET_NO_NEW_PRIVS +#define PR_SET_NO_NEW_PRIVS 38 +#endif + +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; +} diff --git a/samples/seccomp/bpf-helper.c b/samples/seccomp/bpf-helper.c new file mode 100644 index 000000000..05cb4d5ff --- /dev/null +++ b/samples/seccomp/bpf-helper.c @@ -0,0 +1,95 @@ +/* + * Seccomp BPF helper functions + * + * Copyright (c) 2012 The Chromium OS Authors <chromium-os-dev@chromium.org> + * Author: Will Drewry <wad@chromium.org> + * + * 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 <stdio.h> +#include <stdlib.h> +#include <string.h> + +#include "bpf-helper.h" + +int bpf_resolve_jumps(struct bpf_labels *labels, + struct sock_filter *filter, size_t count) +{ + struct sock_filter *begin = filter; + __u8 insn = count - 1; + + if (count < 1) + return -1; + /* + * Walk it once, backwards, to build the label table and do fixups. + * Since backward jumps are disallowed by BPF, this is easy. + */ + filter += insn; + for (; filter >= begin; --insn, --filter) { + if (filter->code != (BPF_JMP+BPF_JA)) + continue; + switch ((filter->jt<<8)|filter->jf) { + case (JUMP_JT<<8)|JUMP_JF: + if (labels->labels[filter->k].location == 0xffffffff) { + fprintf(stderr, "Unresolved label: '%s'\n", + labels->labels[filter->k].label); + return 1; + } + filter->k = labels->labels[filter->k].location - + (insn + 1); + filter->jt = 0; + filter->jf = 0; + continue; + case (LABEL_JT<<8)|LABEL_JF: + if (labels->labels[filter->k].location != 0xffffffff) { + fprintf(stderr, "Duplicate label use: '%s'\n", + labels->labels[filter->k].label); + return 1; + } + labels->labels[filter->k].location = insn; + filter->k = 0; /* fall through */ + filter->jt = 0; + filter->jf = 0; + continue; + } + } + return 0; +} + +/* Simple lookup table for labels. */ +__u32 seccomp_bpf_label(struct bpf_labels *labels, const char *label) +{ + struct __bpf_label *begin = labels->labels, *end; + int id; + + if (labels->count == BPF_LABELS_MAX) { + fprintf(stderr, "Too many labels\n"); + exit(1); + } + if (labels->count == 0) { + begin->label = label; + begin->location = 0xffffffff; + labels->count++; + return 0; + } + end = begin + labels->count; + for (id = 0; begin < end; ++begin, ++id) { + if (!strcmp(label, begin->label)) + return id; + } + begin->label = label; + begin->location = 0xffffffff; + labels->count++; + return id; +} + +void seccomp_bpf_print(struct sock_filter *filter, size_t count) +{ + struct sock_filter *end = filter + count; + for ( ; filter < end; ++filter) + printf("{ code=%u,jt=%u,jf=%u,k=%u },\n", + filter->code, filter->jt, filter->jf, filter->k); +} diff --git a/samples/seccomp/bpf-helper.h b/samples/seccomp/bpf-helper.h new file mode 100644 index 000000000..38ee70f3c --- /dev/null +++ b/samples/seccomp/bpf-helper.h @@ -0,0 +1,243 @@ +/* + * Example wrapper around BPF macros. + * + * Copyright (c) 2012 The Chromium OS Authors <chromium-os-dev@chromium.org> + * Author: Will Drewry <wad@chromium.org> + * + * The code may be used by anyone for any purpose, + * and can serve as a starting point for developing + * applications using prctl(PR_SET_SECCOMP, 2, ...). + * + * No guarantees are provided with respect to the correctness + * or functionality of this code. + */ +#ifndef __BPF_HELPER_H__ +#define __BPF_HELPER_H__ + +#include <asm/bitsperlong.h> /* for __BITS_PER_LONG */ +#include <endian.h> +#include <linux/filter.h> +#include <linux/seccomp.h> /* for seccomp_data */ +#include <linux/types.h> +#include <linux/unistd.h> +#include <stddef.h> + +#define BPF_LABELS_MAX 256 +struct bpf_labels { + int count; + struct __bpf_label { + const char *label; + __u32 location; + } labels[BPF_LABELS_MAX]; +}; + +int bpf_resolve_jumps(struct bpf_labels *labels, + struct sock_filter *filter, size_t count); +__u32 seccomp_bpf_label(struct bpf_labels *labels, const char *label); +void seccomp_bpf_print(struct sock_filter *filter, size_t count); + +#define JUMP_JT 0xff +#define JUMP_JF 0xff +#define LABEL_JT 0xfe +#define LABEL_JF 0xfe + +#define ALLOW \ + BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW) +#define DENY \ + BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_KILL) +#define JUMP(labels, label) \ + BPF_JUMP(BPF_JMP+BPF_JA, FIND_LABEL((labels), (label)), \ + JUMP_JT, JUMP_JF) +#define LABEL(labels, label) \ + BPF_JUMP(BPF_JMP+BPF_JA, FIND_LABEL((labels), (label)), \ + LABEL_JT, LABEL_JF) +#define SYSCALL(nr, jt) \ + BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (nr), 0, 1), \ + jt + +/* Lame, but just an example */ +#define FIND_LABEL(labels, label) seccomp_bpf_label((labels), #label) + +#define EXPAND(...) __VA_ARGS__ + +/* Ensure that we load the logically correct offset. */ +#if __BYTE_ORDER == __LITTLE_ENDIAN +#define LO_ARG(idx) offsetof(struct seccomp_data, args[(idx)]) +#elif __BYTE_ORDER == __BIG_ENDIAN +#define LO_ARG(idx) offsetof(struct seccomp_data, args[(idx)]) + sizeof(__u32) +#else +#error "Unknown endianness" +#endif + +/* Map all width-sensitive operations */ +#if __BITS_PER_LONG == 32 + +#define JEQ(x, jt) JEQ32(x, EXPAND(jt)) +#define JNE(x, jt) JNE32(x, EXPAND(jt)) +#define JGT(x, jt) JGT32(x, EXPAND(jt)) +#define JLT(x, jt) JLT32(x, EXPAND(jt)) +#define JGE(x, jt) JGE32(x, EXPAND(jt)) +#define JLE(x, jt) JLE32(x, EXPAND(jt)) +#define JA(x, jt) JA32(x, EXPAND(jt)) +#define ARG(i) ARG_32(i) + +#elif __BITS_PER_LONG == 64 + +/* Ensure that we load the logically correct offset. */ +#if __BYTE_ORDER == __LITTLE_ENDIAN +#define ENDIAN(_lo, _hi) _lo, _hi +#define HI_ARG(idx) offsetof(struct seccomp_data, args[(idx)]) + sizeof(__u32) +#elif __BYTE_ORDER == __BIG_ENDIAN +#define ENDIAN(_lo, _hi) _hi, _lo +#define HI_ARG(idx) offsetof(struct seccomp_data, args[(idx)]) +#endif + +union arg64 { + struct { + __u32 ENDIAN(lo32, hi32); + }; + __u64 u64; +}; + +#define JEQ(x, jt) \ + JEQ64(((union arg64){.u64 = (x)}).lo32, \ + ((union arg64){.u64 = (x)}).hi32, \ + EXPAND(jt)) +#define JGT(x, jt) \ + JGT64(((union arg64){.u64 = (x)}).lo32, \ + ((union arg64){.u64 = (x)}).hi32, \ + EXPAND(jt)) +#define JGE(x, jt) \ + JGE64(((union arg64){.u64 = (x)}).lo32, \ + ((union arg64){.u64 = (x)}).hi32, \ + EXPAND(jt)) +#define JNE(x, jt) \ + JNE64(((union arg64){.u64 = (x)}).lo32, \ + ((union arg64){.u64 = (x)}).hi32, \ + EXPAND(jt)) +#define JLT(x, jt) \ + JLT64(((union arg64){.u64 = (x)}).lo32, \ + ((union arg64){.u64 = (x)}).hi32, \ + EXPAND(jt)) +#define JLE(x, jt) \ + JLE64(((union arg64){.u64 = (x)}).lo32, \ + ((union arg64){.u64 = (x)}).hi32, \ + EXPAND(jt)) + +#define JA(x, jt) \ + JA64(((union arg64){.u64 = (x)}).lo32, \ + ((union arg64){.u64 = (x)}).hi32, \ + EXPAND(jt)) +#define ARG(i) ARG_64(i) + +#else +#error __BITS_PER_LONG value unusable. +#endif + +/* Loads the arg into A */ +#define ARG_32(idx) \ + BPF_STMT(BPF_LD+BPF_W+BPF_ABS, LO_ARG(idx)) + +/* Loads hi into A and lo in X */ +#define ARG_64(idx) \ + BPF_STMT(BPF_LD+BPF_W+BPF_ABS, LO_ARG(idx)), \ + BPF_STMT(BPF_ST, 0), /* lo -> M[0] */ \ + BPF_STMT(BPF_LD+BPF_W+BPF_ABS, HI_ARG(idx)), \ + BPF_STMT(BPF_ST, 1) /* hi -> M[1] */ + +#define JEQ32(value, jt) \ + BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (value), 0, 1), \ + jt + +#define JNE32(value, jt) \ + BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (value), 1, 0), \ + jt + +/* Checks the lo, then swaps to check the hi. A=lo,X=hi */ +#define JEQ64(lo, hi, jt) \ + BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (hi), 0, 5), \ + BPF_STMT(BPF_LD+BPF_MEM, 0), /* swap in lo */ \ + BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (lo), 0, 2), \ + BPF_STMT(BPF_LD+BPF_MEM, 1), /* passed: swap hi back in */ \ + jt, \ + BPF_STMT(BPF_LD+BPF_MEM, 1) /* failed: swap hi back in */ + +#define JNE64(lo, hi, jt) \ + BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (hi), 5, 0), \ + BPF_STMT(BPF_LD+BPF_MEM, 0), /* swap in lo */ \ + BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (lo), 2, 0), \ + BPF_STMT(BPF_LD+BPF_MEM, 1), /* passed: swap hi back in */ \ + jt, \ + BPF_STMT(BPF_LD+BPF_MEM, 1) /* failed: swap hi back in */ + +#define JA32(value, jt) \ + BPF_JUMP(BPF_JMP+BPF_JSET+BPF_K, (value), 0, 1), \ + jt + +#define JA64(lo, hi, jt) \ + BPF_JUMP(BPF_JMP+BPF_JSET+BPF_K, (hi), 3, 0), \ + BPF_STMT(BPF_LD+BPF_MEM, 0), /* swap in lo */ \ + BPF_JUMP(BPF_JMP+BPF_JSET+BPF_K, (lo), 0, 2), \ + BPF_STMT(BPF_LD+BPF_MEM, 1), /* passed: swap hi back in */ \ + jt, \ + BPF_STMT(BPF_LD+BPF_MEM, 1) /* failed: swap hi back in */ + +#define JGE32(value, jt) \ + BPF_JUMP(BPF_JMP+BPF_JGE+BPF_K, (value), 0, 1), \ + jt + +#define JLT32(value, jt) \ + BPF_JUMP(BPF_JMP+BPF_JGE+BPF_K, (value), 1, 0), \ + jt + +/* Shortcut checking if hi > arg.hi. */ +#define JGE64(lo, hi, jt) \ + BPF_JUMP(BPF_JMP+BPF_JGT+BPF_K, (hi), 4, 0), \ + BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (hi), 0, 5), \ + BPF_STMT(BPF_LD+BPF_MEM, 0), /* swap in lo */ \ + BPF_JUMP(BPF_JMP+BPF_JGE+BPF_K, (lo), 0, 2), \ + BPF_STMT(BPF_LD+BPF_MEM, 1), /* passed: swap hi back in */ \ + jt, \ + BPF_STMT(BPF_LD+BPF_MEM, 1) /* failed: swap hi back in */ + +#define JLT64(lo, hi, jt) \ + BPF_JUMP(BPF_JMP+BPF_JGE+BPF_K, (hi), 0, 4), \ + BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (hi), 0, 5), \ + BPF_STMT(BPF_LD+BPF_MEM, 0), /* swap in lo */ \ + BPF_JUMP(BPF_JMP+BPF_JGT+BPF_K, (lo), 2, 0), \ + BPF_STMT(BPF_LD+BPF_MEM, 1), /* passed: swap hi back in */ \ + jt, \ + BPF_STMT(BPF_LD+BPF_MEM, 1) /* failed: swap hi back in */ + +#define JGT32(value, jt) \ + BPF_JUMP(BPF_JMP+BPF_JGT+BPF_K, (value), 0, 1), \ + jt + +#define JLE32(value, jt) \ + BPF_JUMP(BPF_JMP+BPF_JGT+BPF_K, (value), 1, 0), \ + jt + +/* Check hi > args.hi first, then do the GE checking */ +#define JGT64(lo, hi, jt) \ + BPF_JUMP(BPF_JMP+BPF_JGT+BPF_K, (hi), 4, 0), \ + BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (hi), 0, 5), \ + BPF_STMT(BPF_LD+BPF_MEM, 0), /* swap in lo */ \ + BPF_JUMP(BPF_JMP+BPF_JGT+BPF_K, (lo), 0, 2), \ + BPF_STMT(BPF_LD+BPF_MEM, 1), /* passed: swap hi back in */ \ + jt, \ + BPF_STMT(BPF_LD+BPF_MEM, 1) /* failed: swap hi back in */ + +#define JLE64(lo, hi, jt) \ + BPF_JUMP(BPF_JMP+BPF_JGT+BPF_K, (hi), 6, 0), \ + BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (hi), 0, 3), \ + BPF_STMT(BPF_LD+BPF_MEM, 0), /* swap in lo */ \ + BPF_JUMP(BPF_JMP+BPF_JGT+BPF_K, (lo), 2, 0), \ + BPF_STMT(BPF_LD+BPF_MEM, 1), /* passed: swap hi back in */ \ + jt, \ + BPF_STMT(BPF_LD+BPF_MEM, 1) /* failed: swap hi back in */ + +#define LOAD_SYSCALL_NR \ + BPF_STMT(BPF_LD+BPF_W+BPF_ABS, \ + offsetof(struct seccomp_data, nr)) + +#endif /* __BPF_HELPER_H__ */ diff --git a/samples/seccomp/dropper.c b/samples/seccomp/dropper.c new file mode 100644 index 000000000..c69c347c7 --- /dev/null +++ b/samples/seccomp/dropper.c @@ -0,0 +1,68 @@ +/* + * Naive system call dropper built on seccomp_filter. + * + * Copyright (c) 2012 The Chromium OS Authors <chromium-os-dev@chromium.org> + * Author: Will Drewry <wad@chromium.org> + * + * The code may be used by anyone for any purpose, + * and can serve as a starting point for developing + * applications using prctl(PR_SET_SECCOMP, 2, ...). + * + * When run, returns the specified errno for the specified + * system call number against the given architecture. + * + * Run this one as root as PR_SET_NO_NEW_PRIVS is not called. + */ + +#include <errno.h> +#include <linux/audit.h> +#include <linux/filter.h> +#include <linux/seccomp.h> +#include <linux/unistd.h> +#include <stdio.h> +#include <stddef.h> +#include <stdlib.h> +#include <sys/prctl.h> +#include <unistd.h> + +static int install_filter(int nr, int arch, int error) +{ + struct sock_filter filter[] = { + BPF_STMT(BPF_LD+BPF_W+BPF_ABS, + (offsetof(struct seccomp_data, arch))), + BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, arch, 0, 3), + BPF_STMT(BPF_LD+BPF_W+BPF_ABS, + (offsetof(struct seccomp_data, nr))), + BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, nr, 0, 1), + BPF_STMT(BPF_RET+BPF_K, + SECCOMP_RET_ERRNO|(error & SECCOMP_RET_DATA)), + BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW), + }; + struct sock_fprog prog = { + .len = (unsigned short)(sizeof(filter)/sizeof(filter[0])), + .filter = filter, + }; + if (prctl(PR_SET_SECCOMP, 2, &prog)) { + perror("prctl"); + return 1; + } + return 0; +} + +int main(int argc, char **argv) +{ + if (argc < 5) { + fprintf(stderr, "Usage:\n" + "dropper <syscall_nr> <arch> <errno> <prog> [<args>]\n" + "Hint: AUDIT_ARCH_I386: 0x%X\n" + " AUDIT_ARCH_X86_64: 0x%X\n" + "\n", AUDIT_ARCH_I386, AUDIT_ARCH_X86_64); + return 1; + } + if (install_filter(strtol(argv[1], NULL, 0), strtol(argv[2], NULL, 0), + strtol(argv[3], NULL, 0))) + return 1; + execv(argv[4], &argv[4]); + printf("Failed to execv\n"); + return 255; +} |