seccomp - operate on Secure Computing state of the process
#include <linux/seccomp.h>
#include <linux/filter.h>
#include <linux/audit.h>
#include <linux/signal.h>
#include <sys/ptrace.h>
int seccomp(unsigned int operation, unsigned int flags, void *args);
The
seccomp() system call operates on the Secure Computing (seccomp)
state of the calling process.
Currently, Linux supports the following
operation values:
- SECCOMP_SET_MODE_STRICT
- The only system calls that the calling thread is permitted to make are
read(2), write(2), _exit(2) (but not
exit_group(2)), and sigreturn(2). Other system calls result
in the delivery of a SIGKILL signal. Strict secure computing mode
is useful for number-crunching applications that may need to execute
untrusted byte code, perhaps obtained by reading from a pipe or
socket.
- Note that although the calling thread can no longer call
sigprocmask(2), it can use sigreturn(2) to block all signals
apart from SIGKILL and SIGSTOP. This means that
alarm(2) (for example) is not sufficient for restricting the
process's execution time. Instead, to reliably terminate the process,
SIGKILL must be used. This can be done by using
timer_create(2) with SIGEV_SIGNAL and sigev_signo set
to SIGKILL, or by using setrlimit(2) to set the hard limit
for RLIMIT_CPU.
- This operation is available only if the kernel is configured with
CONFIG_SECCOMP enabled.
- The value of flags must be 0, and args must be NULL.
- This operation is functionally identical to the call:
-
prctl(PR_SET_SECCOMP, SECCOMP_MODE_STRICT);
- SECCOMP_SET_MODE_FILTER
- The system calls allowed are defined by a pointer to a Berkeley Packet
Filter (BPF) passed via args. This argument is a pointer to a
struct sock_fprog; it can be designed to filter arbitrary
system calls and system call arguments. If the filter is invalid,
seccomp() fails, returning EINVAL in errno.
- If fork(2) or clone(2) is allowed by the filter, any child
processes will be constrained to the same system call filters as the
parent. If execve(2) is allowed, the existing filters will be
preserved across a call to execve(2).
- In order to use the SECCOMP_SET_MODE_FILTER operation, either the
calling thread must have the CAP_SYS_ADMIN capability in its user
namespace, or the thread must already have the no_new_privs bit
set. If that bit was not already set by an ancestor of this thread, the
thread must make the following call:
-
prctl(PR_SET_NO_NEW_PRIVS, 1);
- Otherwise, the SECCOMP_SET_MODE_FILTER operation fails and returns
EACCES in errno. This requirement ensures that an
unprivileged process cannot apply a malicious filter and then invoke a
set-user-ID or other privileged program using execve(2), thus
potentially compromising that program. (Such a malicious filter might, for
example, cause an attempt to use setuid(2) to set the caller's user
IDs to nonzero values to instead return 0 without actually making the
system call. Thus, the program might be tricked into retaining superuser
privileges in circumstances where it is possible to influence it to do
dangerous things because it did not actually drop privileges.)
- If prctl(2) or seccomp() is allowed by the attached filter,
further filters may be added. This will increase evaluation time, but
allows for further reduction of the attack surface during execution of a
thread.
- The SECCOMP_SET_MODE_FILTER operation is available only if the
kernel is configured with CONFIG_SECCOMP_FILTER enabled.
- When flags is 0, this operation is functionally identical to the
call:
-
prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, args);
- The recognized flags are:
- SECCOMP_FILTER_FLAG_TSYNC
- When adding a new filter, synchronize all other threads of the calling
process to the same seccomp filter tree. A "filter tree" is the
ordered list of filters attached to a thread. (Attaching identical filters
in separate seccomp() calls results in different filters from this
perspective.)
- If any thread cannot synchronize to the same filter tree, the call will
not attach the new seccomp filter, and will fail, returning the first
thread ID found that cannot synchronize. Synchronization will fail if
another thread in the same process is in SECCOMP_MODE_STRICT or if
it has attached new seccomp filters to itself, diverging from the calling
thread's filter tree.
- SECCOMP_FILTER_FLAG_LOG (since Linux 4.14)
- All filter return actions except SECCOMP_RET_ALLOW should be
logged. An administrator may override this filter flag by preventing
specific actions from being logged via the
/proc/sys/kernel/seccomp/actions_logged file.
- SECCOMP_FILTER_FLAG_SPEC_ALLOW (since Linux 4.17)
- Disable Speculative Store Bypass mitigation.
- SECCOMP_GET_ACTION_AVAIL (since Linux 4.14)
- Test to see if an action is supported by the kernel. This operation is
helpful to confirm that the kernel knows of a more recently added filter
return action since the kernel treats all unknown actions as
SECCOMP_RET_KILL_PROCESS.
- The value of flags must be 0, and args must be a pointer to
an unsigned 32-bit filter return action.
When adding filters via
SECCOMP_SET_MODE_FILTER,
args points to a
filter program:
struct sock_fprog {
unsigned short len; /* Number of BPF instructions */
struct sock_filter *filter; /* Pointer to array of
BPF instructions */
};
Each program must contain one or more BPF instructions:
struct sock_filter { /* Filter block */
__u16 code; /* Actual filter code */
__u8 jt; /* Jump true */
__u8 jf; /* Jump false */
__u32 k; /* Generic multiuse field */
};
When executing the instructions, the BPF program operates on the system call
information made available (i.e., use the
BPF_ABS addressing mode) as a
(read-only) buffer of the following form:
struct seccomp_data {
int nr; /* System call number */
__u32 arch; /* AUDIT_ARCH_* value
(see <linux/audit.h>) */
__u64 instruction_pointer; /* CPU instruction pointer */
__u64 args[6]; /* Up to 6 system call arguments */
};
Because numbering of system calls varies between architectures and some
architectures (e.g., x86-64) allow user-space code to use the calling
conventions of multiple architectures (and the convention being used may vary
over the life of a process that uses
execve(2) to execute binaries that
employ the different conventions), it is usually necessary to verify the value
of the
arch field.
It is strongly recommended to use an allow-list approach whenever possible
because such an approach is more robust and simple. A deny-list will have to
be updated whenever a potentially dangerous system call is added (or a
dangerous flag or option if those are deny-listed), and it is often possible
to alter the representation of a value without altering its meaning, leading
to a deny-list bypass. See also
Caveats below.
The
arch field is not unique for all calling conventions. The x86-64 ABI
and the x32 ABI both use
AUDIT_ARCH_X86_64 as
arch, and they run
on the same processors. Instead, the mask
__X32_SYSCALL_BIT is used on
the system call number to tell the two ABIs apart.
This means that in order to create a seccomp-based deny-list for system calls
performed through the x86-64 ABI, it is necessary to not only check that
arch equals
AUDIT_ARCH_X86_64, but also to explicitly reject all
system calls that contain
__X32_SYSCALL_BIT in
nr.
The
instruction_pointer field provides the address of the
machine-language instruction that performed the system call. This might be
useful in conjunction with the use of
/proc/[pid]/maps to perform
checks based on which region (mapping) of the program made the system call.
(Probably, it is wise to lock down the
mmap(2) and
mprotect(2)
system calls to prevent the program from subverting such checks.)
When checking values from
args against a deny-list, keep in mind that
arguments are often silently truncated before being processed, but after the
seccomp check. For example, this happens if the i386 ABI is used on an x86-64
kernel: although the kernel will normally not look beyond the 32 lowest bits
of the arguments, the values of the full 64-bit registers will be present in
the seccomp data. A less surprising example is that if the x86-64 ABI is used
to perform a system call that takes an argument of type
int, the
more-significant half of the argument register is ignored by the system call,
but visible in the seccomp data.
A seccomp filter returns a 32-bit value consisting of two parts: the most
significant 16 bits (corresponding to the mask defined by the constant
SECCOMP_RET_ACTION_FULL) contain one of the "action" values
listed below; the least significant 16-bits (defined by the constant
SECCOMP_RET_DATA) are "data" to be associated with this
return value.
If multiple filters exist, they are
all executed, in reverse order of
their addition to the filter tree—that is, the most recently installed
filter is executed first. (Note that all filters will be called even if one of
the earlier filters returns
SECCOMP_RET_KILL. This is done to simplify
the kernel code and to provide a tiny speed-up in the execution of sets of
filters by avoiding a check for this uncommon case.) The return value for the
evaluation of a given system call is the first-seen action value of highest
precedence (along with its accompanying data) returned by execution of all of
the filters.
In decreasing order of precedence, the action values that may be returned by a
seccomp filter are:
- SECCOMP_RET_KILL_PROCESS (since Linux 4.14)
- This value results in immediate termination of the process, with a core
dump. The system call is not executed. By contrast with
SECCOMP_RET_KILL_THREAD below, all threads in the thread group are
terminated. (For a discussion of thread groups, see the description of the
CLONE_THREAD flag in clone(2).)
- The process terminates as though killed by a SIGSYS signal.
Even if a signal handler has been registered for SIGSYS, the
handler will be ignored in this case and the process always terminates. To
a parent process that is waiting on this process (using waitpid(2)
or similar), the returned wstatus will indicate that its child was
terminated as though by a SIGSYS signal.
- SECCOMP_RET_KILL_THREAD (or SECCOMP_RET_KILL)
- This value results in immediate termination of the thread that made the
system call. The system call is not executed. Other threads in the same
thread group will continue to execute.
- The thread terminates as though killed by a SIGSYS signal.
See SECCOMP_RET_KILL_PROCESS above.
- Before Linux 4.11, any process terminated in this way would not trigger a
coredump (even though SIGSYS is documented in signal(7) as
having a default action of termination with a core dump). Since Linux
4.11, a single-threaded process will dump core if terminated in this
way.
- With the addition of SECCOMP_RET_KILL_PROCESS in Linux 4.14,
SECCOMP_RET_KILL_THREAD was added as a synonym for
SECCOMP_RET_KILL, in order to more clearly distinguish the two
actions.
- SECCOMP_RET_TRAP
- This value results in the kernel sending a thread-directed SIGSYS
signal to the triggering thread. (The system call is not executed.)
Various fields will be set in the siginfo_t structure (see
sigaction(2)) associated with signal:
- *
- si_signo will contain SIGSYS.
- *
- si_call_addr will show the address of the system call
instruction.
- *
- si_syscall and si_arch will indicate which system call was
attempted.
- *
- si_code will contain SYS_SECCOMP.
- *
- si_errno will contain the SECCOMP_RET_DATA portion of the
filter return value.
- The program counter will be as though the system call happened (i.e., the
program counter will not point to the system call instruction). The return
value register will contain an architecture-dependent value; if resuming
execution, set it to something appropriate for the system call. (The
architecture dependency is because replacing it with ENOSYS could
overwrite some useful information.)
- SECCOMP_RET_ERRNO
- This value results in the SECCOMP_RET_DATA portion of the filter's
return value being passed to user space as the errno value without
executing the system call.
- SECCOMP_RET_TRACE
- When returned, this value will cause the kernel to attempt to notify a
ptrace(2)-based tracer prior to executing the system call. If there
is no tracer present, the system call is not executed and returns a
failure status with errno set to ENOSYS.
- A tracer will be notified if it requests PTRACE_O_TRACESECCOMP
using ptrace(PTRACE_SETOPTIONS). The tracer will be notified of a
PTRACE_EVENT_SECCOMP and the SECCOMP_RET_DATA portion of the
filter's return value will be available to the tracer via
PTRACE_GETEVENTMSG.
- The tracer can skip the system call by changing the system call number to
-1. Alternatively, the tracer can change the system call requested by
changing the system call to a valid system call number. If the tracer asks
to skip the system call, then the system call will appear to return the
value that the tracer puts in the return value register.
- Before kernel 4.8, the seccomp check will not be run again after the
tracer is notified. (This means that, on older kernels, seccomp-based
sandboxes must not allow use of ptrace(2)—even of
other sandboxed processes—without extreme care; ptracers can use
this mechanism to escape from the seccomp sandbox.)
- SECCOMP_RET_LOG (since Linux 4.14)
- This value results in the system call being executed after the filter
return action is logged. An administrator may override the logging of this
action via the /proc/sys/kernel/seccomp/actions_logged file.
- SECCOMP_RET_ALLOW
- This value results in the system call being executed.
If an action value other than one of the above is specified, then the filter
action is treated as either
SECCOMP_RET_KILL_PROCESS (since Linux 4.14)
or
SECCOMP_RET_KILL_THREAD (in Linux 4.13 and earlier).
The files in the directory
/proc/sys/kernel/seccomp provide additional
seccomp information and configuration:
- actions_avail (since Linux 4.14)
- A read-only ordered list of seccomp filter return actions in string form.
The ordering, from left-to-right, is in decreasing order of precedence.
The list represents the set of seccomp filter return actions supported by
the kernel.
- actions_logged (since Linux 4.14)
- A read-write ordered list of seccomp filter return actions that are
allowed to be logged. Writes to the file do not need to be in ordered form
but reads from the file will be ordered in the same way as the
actions_avail file.
- It is important to note that the value of actions_logged does not
prevent certain filter return actions from being logged when the audit
subsystem is configured to audit a task. If the action is not found in the
actions_logged file, the final decision on whether to audit the
action for that task is ultimately left up to the audit subsystem to
decide for all filter return actions other than
SECCOMP_RET_ALLOW.
- The "allow" string is not accepted in the actions_logged
file as it is not possible to log SECCOMP_RET_ALLOW actions.
Attempting to write "allow" to the file will fail with the error
EINVAL.
Since Linux 4.14, the kernel provides the facility to log the actions returned
by seccomp filters in the audit log. The kernel makes the decision to log an
action based on the action type, whether or not the action is present in the
actions_logged file, and whether kernel auditing is enabled (e.g., via
the kernel boot option
audit=1). The rules are as follows:
- *
- If the action is SECCOMP_RET_ALLOW, the action is not logged.
- *
- Otherwise, if the action is either SECCOMP_RET_KILL_PROCESS or
SECCOMP_RET_KILL_THREAD, and that action appears in the
actions_logged file, the action is logged.
- *
- Otherwise, if the filter has requested logging (the
SECCOMP_FILTER_FLAG_LOG flag) and the action appears in the
actions_logged file, the action is logged.
- *
- Otherwise, if kernel auditing is enabled and the process is being audited
(autrace(8)), the action is logged.
- *
- Otherwise, the action is not logged.
On success,
seccomp() returns 0. On error, if
SECCOMP_FILTER_FLAG_TSYNC was used, the return value is the ID of the
thread that caused the synchronization failure. (This ID is a kernel thread ID
of the type returned by
clone(2) and
gettid(2).) On other
errors, -1 is returned, and
errno is set to indicate the cause of the
error.
seccomp() can fail for the following reasons:
- EACCES
- The caller did not have the CAP_SYS_ADMIN capability in its user
namespace, or had not set no_new_privs before using
SECCOMP_SET_MODE_FILTER.
- EFAULT
- args was not a valid address.
- EINVAL
- operation is unknown or is not supported by this kernel version or
configuration.
- EINVAL
- The specified flags are invalid for the given
operation.
- EINVAL
- operation included BPF_ABS, but the specified offset was not
aligned to a 32-bit boundary or exceeded
sizeof(struct seccomp_data).
- EINVAL
- A secure computing mode has already been set, and operation differs
from the existing setting.
- EINVAL
- operation specified SECCOMP_SET_MODE_FILTER, but the filter
program pointed to by args was not valid or the length of the
filter program was zero or exceeded BPF_MAXINSNS (4096)
instructions.
- ENOMEM
- Out of memory.
- ENOMEM
- The total length of all filter programs attached to the calling thread
would exceed MAX_INSNS_PER_PATH (32768) instructions. Note that for
the purposes of calculating this limit, each already existing filter
program incurs an overhead penalty of 4 instructions.
- EOPNOTSUPP
- operation specified SECCOMP_GET_ACTION_AVAIL, but the kernel
does not support the filter return action specified by args.
- ESRCH
- Another thread caused a failure during thread sync, but its ID could not
be determined.
The
seccomp() system call first appeared in Linux 3.17.
The
seccomp() system call is a nonstandard Linux extension.
Rather than hand-coding seccomp filters as shown in the example below, you may
prefer to employ the
libseccomp library, which provides a front-end for
generating seccomp filters.
The
Seccomp field of the
/proc/[pid]/status file provides a method
of viewing the seccomp mode of a process; see
proc(5).
seccomp() provides a superset of the functionality provided by the
prctl(2)
PR_SET_SECCOMP operation (which does not support
flags).
Since Linux 4.4, the
ptrace(2)
PTRACE_SECCOMP_GET_FILTER operation
can be used to dump a process's seccomp filters.
Architecture support for seccomp BPF filtering is available on the following
architectures:
- *
- x86-64, i386, x32 (since Linux 3.5)
- *
- ARM (since Linux 3.8)
- *
- s390 (since Linux 3.8)
- *
- MIPS (since Linux 3.16)
- *
- ARM-64 (since Linux 3.19)
- *
- PowerPC (since Linux 4.3)
- *
- Tile (since Linux 4.3)
- *
- PA-RISC (since Linux 4.6)
There are various subtleties to consider when applying seccomp filters to a
program, including the following:
- *
- Some traditional system calls have user-space implementations in the
vdso(7) on many architectures. Notable examples include
clock_gettime(2), gettimeofday(2), and time(2). On
such architectures, seccomp filtering for these system calls will have no
effect. (However, there are cases where the vdso(7) implementations
may fall back to invoking the true system call, in which case seccomp
filters would see the system call.)
- *
- Seccomp filtering is based on system call numbers. However, applications
typically do not directly invoke system calls, but instead call wrapper
functions in the C library which in turn invoke the system calls.
Consequently, one must be aware of the following:
- •
- The glibc wrappers for some traditional system calls may actually employ
system calls with different names in the kernel. For example, the
exit(2) wrapper function actually employs the exit_group(2)
system call, and the fork(2) wrapper function actually calls
clone(2).
- •
- The behavior of wrapper functions may vary across architectures, according
to the range of system calls provided on those architectures. In other
words, the same wrapper function may invoke different system calls on
different architectures.
- •
- Finally, the behavior of wrapper functions can change across glibc
versions. For example, in older versions, the glibc wrapper function for
open(2) invoked the system call of the same name, but starting in
glibc 2.26, the implementation switched to calling openat(2) on all
architectures.
The consequence of the above points is that it may be necessary to filter for a
system call other than might be expected. Various manual pages in Section 2
provide helpful details about the differences between wrapper functions and
the underlying system calls in subsections entitled
C library/kernel
differences.
Furthermore, note that the application of seccomp filters even risks causing
bugs in an application, when the filters cause unexpected failures for
legitimate operations that the application might need to perform. Such bugs
may not easily be discovered when testing the seccomp filters if the bugs
occur in rarely used application code paths.
Note the following BPF details specific to seccomp filters:
- *
- The BPF_H and BPF_B size modifiers are not supported: all
operations must load and store (4-byte) words (BPF_W).
- *
- To access the contents of the seccomp_data buffer, use the
BPF_ABS addressing mode modifier.
- *
- The BPF_LEN addressing mode modifier yields an immediate mode
operand whose value is the size of the seccomp_data buffer.
The program below accepts four or more arguments. The first three arguments are
a system call number, a numeric architecture identifier, and an error number.
The program uses these values to construct a BPF filter that is used at run
time to perform the following checks:
- [1]
- If the program is not running on the specified architecture, the BPF
filter causes system calls to fail with the error ENOSYS.
- [2]
- If the program attempts to execute the system call with the specified
number, the BPF filter causes the system call to fail, with errno
being set to the specified error number.
The remaining command-line arguments specify the pathname and additional
arguments of a program that the example program should attempt to execute
using
execv(3) (a library function that employs the
execve(2)
system call). Some example runs of the program are shown below.
First, we display the architecture that we are running on (x86-64) and then
construct a shell function that looks up system call numbers on this
architecture:
$ uname -m
x86_64
$ syscall_nr() {
cat /usr/src/linux/arch/x86/syscalls/syscall_64.tbl | \
awk '$2 != "x32" && $3 == "'$1'" { print $1 }'
}
When the BPF filter rejects a system call (case [2] above), it causes the system
call to fail with the error number specified on the command line. In the
experiments shown here, we'll use error number 99:
$ errno 99
EADDRNOTAVAIL 99 Cannot assign requested address
In the following example, we attempt to run the command
whoami(1), but
the BPF filter rejects the
execve(2) system call, so that the command
is not even executed:
$ syscall_nr execve
59
$ ./a.out
Usage: ./a.out <syscall_nr> <arch> <errno> <prog> [<args>]
Hint for <arch>: AUDIT_ARCH_I386: 0x40000003
AUDIT_ARCH_X86_64: 0xC000003E
$ ./a.out 59 0xC000003E 99 /bin/whoami
execv: Cannot assign requested address
In the next example, the BPF filter rejects the
write(2) system call, so
that, although it is successfully started, the
whoami(1) command is not
able to write output:
$ syscall_nr write
1
$ ./a.out 1 0xC000003E 99 /bin/whoami
In the final example, the BPF filter rejects a system call that is not used by
the
whoami(1) command, so it is able to successfully execute and
produce output:
$ syscall_nr preadv
295
$ ./a.out 295 0xC000003E 99 /bin/whoami
cecilia
#include <errno.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <linux/audit.h>
#include <linux/filter.h>
#include <linux/seccomp.h>
#include <sys/prctl.h>
#define X32_SYSCALL_BIT 0x40000000
static int
install_filter(int syscall_nr, int t_arch, int f_errno)
{
unsigned int upper_nr_limit = 0xffffffff;
/* Assume that AUDIT_ARCH_X86_64 means the normal x86-64 ABI
(in the x32 ABI, all system calls have bit 30 set in the
'nr' field, meaning the numbers are >= X32_SYSCALL_BIT) */
if (t_arch == AUDIT_ARCH_X86_64)
upper_nr_limit = X32_SYSCALL_BIT - 1;
struct sock_filter filter[] = {
/* [0] Load architecture from 'seccomp_data' buffer into
accumulator */
BPF_STMT(BPF_LD | BPF_W | BPF_ABS,
(offsetof(struct seccomp_data, arch))),
/* [1] Jump forward 5 instructions if architecture does not
match 't_arch' */
BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, t_arch, 0, 5),
/* [2] Load system call number from 'seccomp_data' buffer into
accumulator */
BPF_STMT(BPF_LD | BPF_W | BPF_ABS,
(offsetof(struct seccomp_data, nr))),
/* [3] Check ABI - only needed for x86-64 in deny-list use
cases. Use BPF_JGT instead of checking against the bit
mask to avoid having to reload the syscall number. */
BPF_JUMP(BPF_JMP | BPF_JGT | BPF_K, upper_nr_limit, 3, 0),
/* [4] Jump forward 1 instruction if system call number
does not match 'syscall_nr' */
BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, syscall_nr, 0, 1),
/* [5] Matching architecture and system call: don't execute
the system call, and return 'f_errno' in 'errno' */
BPF_STMT(BPF_RET | BPF_K,
SECCOMP_RET_ERRNO | (f_errno & SECCOMP_RET_DATA)),
/* [6] Destination of system call number mismatch: allow other
system calls */
BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ALLOW),
/* [7] Destination of architecture mismatch: kill task */
BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_KILL),
};
struct sock_fprog prog = {
.len = (unsigned short) (sizeof(filter) / sizeof(filter[0])),
.filter = filter,
};
if (seccomp(SECCOMP_SET_MODE_FILTER, 0, &prog)) {
perror("seccomp");
return 1;
}
return 0;
}
int
main(int argc, char **argv)
{
if (argc < 5) {
fprintf(stderr, "Usage: "
"%s <syscall_nr> <arch> <errno> <prog> [<args>]\n"
"Hint for <arch>: AUDIT_ARCH_I386: 0x%X\n"
" AUDIT_ARCH_X86_64: 0x%X\n"
"\n", argv[0], AUDIT_ARCH_I386, AUDIT_ARCH_X86_64);
exit(EXIT_FAILURE);
}
if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
perror("prctl");
exit(EXIT_FAILURE);
}
if (install_filter(strtol(argv[1], NULL, 0),
strtol(argv[2], NULL, 0),
strtol(argv[3], NULL, 0)))
exit(EXIT_FAILURE);
execv(argv[4], &argv[4]);
perror("execv");
exit(EXIT_FAILURE);
}
bpfc(1),
strace(1),
bpf(2),
prctl(2),
ptrace(2),
sigaction(2),
proc(5),
signal(7),
socket(7)
Various pages from the
libseccomp library, including:
scmp_sys_resolver(1),
seccomp_init(3),
seccomp_load(3),
seccomp_rule_add(3), and
seccomp_export_bpf(3).
The kernel source files
Documentation/networking/filter.txt and
Documentation/userspace-api/seccomp_filter.rst (or
Documentation/prctl/seccomp_filter.txt before Linux 4.13).
McCanne, S. and Jacobson, V. (1992)
The BSD Packet Filter: A New Architecture
for User-level Packet Capture, Proceedings of the USENIX Winter 1993
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http://www.tcpdump.org/papers/bpf-usenix93.pdf