seccomp

SECCOMP(2)                 Linux Programmer's Manual                SECCOMP(2)



NAME
       seccomp - operate on Secure Computing state of the process

SYNOPSIS
       #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);

DESCRIPTION
       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.

   Filters
       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 a whitelisting approach whenever
       possible because such an approach is more robust and simple.  A
       blacklist will have to be updated whenever a potentially dangerous
       system call is added (or a dangerous flag or option if those are
       blacklisted), and it is often possible to alter the representation of a
       value without altering its meaning, leading to a blacklist 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 blacklist 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 blacklist, 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).

   /proc interfaces
       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.

   Audit logging of seccomp actions
       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.

RETURN VALUE
       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.

ERRORS
       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.

VERSIONS
       The seccomp() system call first appeared in Linux 3.17.

CONFORMING TO
       The seccomp() system call is a nonstandard Linux extension.

NOTES
       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
       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)

   Caveats
       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.

   Seccomp-specific BPF details
       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.

EXAMPLE
       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

   Program source
       #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 blacklist 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);
       }

SEE ALSO
       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 Conference ⟨http://www.tcpdump.org/papers/bpf-usenix93.pdfCOLOPHON
       This page is part of release 5.03 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at
       https://www.kernel.org/doc/man-pages/.



Linux                             2019-03-06                        SECCOMP(2)