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8ac270d1e2
Documents how system call filtering using Berkeley Packet
Filter programs works and how it may be used.
Includes an example for x86 and a semi-generic
example using a macro-based code generator.
Acked-by: Eric Paris <eparis@redhat.com>
Signed-off-by: Will Drewry <wad@chromium.org>
Acked-by: Kees Cook <keescook@chromium.org>
v18: - added acked by
- update no new privs numbers
v17: - remove @compat note and add Pitfalls section for arch checking
(keescook@chromium.org)
v16: -
v15: -
v14: - rebase/nochanges
v13: - rebase on to 88ebdda6159ffc15699f204c33feb3e431bf9bdc
v12: - comment on the ptrace_event use
- update arch support comment
- note the behavior of SECCOMP_RET_DATA when there are multiple filters
(keescook@chromium.org)
- lots of samples/ clean up incl 64-bit bpf-direct support
(markus@chromium.org)
- rebase to linux-next
v11: - overhaul return value language, updates (keescook@chromium.org)
- comment on do_exit(SIGSYS)
v10: - update for SIGSYS
- update for new seccomp_data layout
- update for ptrace option use
v9: - updated bpf-direct.c for SIGILL
v8: - add PR_SET_NO_NEW_PRIVS to the samples.
v7: - updated for all the new stuff in v7: TRAP, TRACE
- only talk about PR_SET_SECCOMP now
- fixed bad JLE32 check (coreyb@linux.vnet.ibm.com)
- adds dropper.c: a simple system call disabler
v6: - tweak the language to note the requirement of
PR_SET_NO_NEW_PRIVS being called prior to use. (luto@mit.edu)
v5: - update sample to use system call arguments
- adds a "fancy" example using a macro-based generator
- cleaned up bpf in the sample
- update docs to mention arguments
- fix prctl value (eparis@redhat.com)
- language cleanup (rdunlap@xenotime.net)
v4: - update for no_new_privs use
- minor tweaks
v3: - call out BPF <-> Berkeley Packet Filter (rdunlap@xenotime.net)
- document use of tentative always-unprivileged
- guard sample compilation for i386 and x86_64
v2: - move code to samples (corbet@lwn.net)
Signed-off-by: James Morris <james.l.morris@oracle.com>
90 lines
2.2 KiB
C
90 lines
2.2 KiB
C
/*
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* Seccomp BPF helper functions
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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_ATTACH_SECCOMP_FILTER).
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*/
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#include <stdio.h>
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#include <string.h>
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#include "bpf-helper.h"
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int bpf_resolve_jumps(struct bpf_labels *labels,
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struct sock_filter *filter, size_t count)
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{
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struct sock_filter *begin = filter;
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__u8 insn = count - 1;
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if (count < 1)
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return -1;
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/*
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* Walk it once, backwards, to build the label table and do fixups.
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* Since backward jumps are disallowed by BPF, this is easy.
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*/
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filter += insn;
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for (; filter >= begin; --insn, --filter) {
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if (filter->code != (BPF_JMP+BPF_JA))
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continue;
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switch ((filter->jt<<8)|filter->jf) {
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case (JUMP_JT<<8)|JUMP_JF:
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if (labels->labels[filter->k].location == 0xffffffff) {
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fprintf(stderr, "Unresolved label: '%s'\n",
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labels->labels[filter->k].label);
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return 1;
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}
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filter->k = labels->labels[filter->k].location -
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(insn + 1);
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filter->jt = 0;
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filter->jf = 0;
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continue;
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case (LABEL_JT<<8)|LABEL_JF:
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if (labels->labels[filter->k].location != 0xffffffff) {
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fprintf(stderr, "Duplicate label use: '%s'\n",
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labels->labels[filter->k].label);
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return 1;
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}
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labels->labels[filter->k].location = insn;
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filter->k = 0; /* fall through */
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filter->jt = 0;
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filter->jf = 0;
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continue;
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}
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}
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return 0;
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}
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/* Simple lookup table for labels. */
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__u32 seccomp_bpf_label(struct bpf_labels *labels, const char *label)
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{
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struct __bpf_label *begin = labels->labels, *end;
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int id;
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if (labels->count == 0) {
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begin->label = label;
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begin->location = 0xffffffff;
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labels->count++;
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return 0;
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}
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end = begin + labels->count;
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for (id = 0; begin < end; ++begin, ++id) {
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if (!strcmp(label, begin->label))
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return id;
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}
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begin->label = label;
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begin->location = 0xffffffff;
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labels->count++;
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return id;
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}
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void seccomp_bpf_print(struct sock_filter *filter, size_t count)
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{
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struct sock_filter *end = filter + count;
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for ( ; filter < end; ++filter)
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printf("{ code=%u,jt=%u,jf=%u,k=%u },\n",
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filter->code, filter->jt, filter->jf, filter->k);
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}
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