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 88ebdda615
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>
102 lines
2.4 KiB
C
102 lines
2.4 KiB
C
/*
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* Seccomp BPF example using a macro-based generator.
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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 <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 <string.h>
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#include <sys/prctl.h>
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#include <unistd.h>
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#include "bpf-helper.h"
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#ifndef PR_SET_NO_NEW_PRIVS
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#define PR_SET_NO_NEW_PRIVS 38
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#endif
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int main(int argc, char **argv)
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{
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struct bpf_labels l;
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static const char msg1[] = "Please type something: ";
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static const char msg2[] = "You typed: ";
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char buf[256];
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struct sock_filter filter[] = {
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/* TODO: LOAD_SYSCALL_NR(arch) and enforce an arch */
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LOAD_SYSCALL_NR,
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SYSCALL(__NR_exit, ALLOW),
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SYSCALL(__NR_exit_group, ALLOW),
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SYSCALL(__NR_write, JUMP(&l, write_fd)),
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SYSCALL(__NR_read, JUMP(&l, read)),
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DENY, /* Don't passthrough into a label */
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LABEL(&l, read),
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ARG(0),
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JNE(STDIN_FILENO, DENY),
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ARG(1),
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JNE((unsigned long)buf, DENY),
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ARG(2),
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JGE(sizeof(buf), DENY),
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ALLOW,
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LABEL(&l, write_fd),
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ARG(0),
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JEQ(STDOUT_FILENO, JUMP(&l, write_buf)),
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JEQ(STDERR_FILENO, JUMP(&l, write_buf)),
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DENY,
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LABEL(&l, write_buf),
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ARG(1),
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JEQ((unsigned long)msg1, JUMP(&l, msg1_len)),
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JEQ((unsigned long)msg2, JUMP(&l, msg2_len)),
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JEQ((unsigned long)buf, JUMP(&l, buf_len)),
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DENY,
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LABEL(&l, msg1_len),
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ARG(2),
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JLT(sizeof(msg1), ALLOW),
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DENY,
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LABEL(&l, msg2_len),
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ARG(2),
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JLT(sizeof(msg2), ALLOW),
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DENY,
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LABEL(&l, buf_len),
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ARG(2),
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JLT(sizeof(buf), ALLOW),
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DENY,
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};
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struct sock_fprog prog = {
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.filter = filter,
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.len = (unsigned short)(sizeof(filter)/sizeof(filter[0])),
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};
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ssize_t bytes;
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bpf_resolve_jumps(&l, filter, sizeof(filter)/sizeof(*filter));
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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, SECCOMP_MODE_FILTER, &prog)) {
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perror("prctl(SECCOMP)");
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return 1;
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}
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syscall(__NR_write, STDOUT_FILENO, msg1, strlen(msg1));
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bytes = syscall(__NR_read, STDIN_FILENO, buf, sizeof(buf)-1);
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bytes = (bytes > 0 ? bytes : 0);
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syscall(__NR_write, STDERR_FILENO, msg2, strlen(msg2));
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syscall(__NR_write, STDERR_FILENO, buf, bytes);
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/* Now get killed */
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syscall(__NR_write, STDERR_FILENO, msg2, strlen(msg2)+2);
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return 0;
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}
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