seccomp_notify_alloc(3) — Linux manual page


seccomp_notify_alloc(3) libseccomp Documentation seccomp_notify_alloc(3)

NAME         top

       seccomp_notify_alloc, seccomp_notify_free,
       seccomp_notify_receive, seccomp_notify_respond,
       seccomp_notify_id_valid, seccomp_notify_fd - Manage seccomp

SYNOPSIS         top

       #include <seccomp.h>

       int seccomp_notify_alloc(struct seccomp_notif **req, struct seccomp_notif_resp **resp)
       void seccomp_notify_free(struct seccomp_notif *req, struct seccomp_notif_resp *resp)
       int seccomp_notify_receive(int fd, struct seccomp_notif *req)
       int seccomp_notify_respond(int fd, struct seccomp_notif_resp *resp)
       int seccomp_notify_id_valid(int fd, uint64_t id)
       int seccomp_notify_fd(const scmp_filter_ctx ctx)

       Link with -lseccomp.

DESCRIPTION         top

       The seccomp_notify_alloc() function dynamically allocates enough
       memory for a seccomp notification and response. Note that one
       should always use these functions and not depend on the structure
       sizes in headers, since the size can vary depending on the kernel
       version. This function takes care to ask the kernel how big each
       structure should be, and allocates the right amount of memory.
       The seccomp_notify_free() function frees memory allocated by

       The seccomp_notify_receive() function receives a notification
       from a seccomp notify fd (obtained from seccomp_notify_fd()).

       The seccomp_notify_respond() function sends a response to a
       particular notification. The id field should be the same as the
       id from the request, so that the kernel knows which request this
       response corresponds to.

       The seccomp_notify_id_valid() function checks to see if the
       syscall from a particular notification request is still valid,
       i.e. if the task is still alive. See NOTES below for details on
       race conditions.

       The seccomp_notify_fd() returns the notification fd of a filter
       after it has been loaded.

RETURN VALUE         top

       The seccomp_notify_fd() returns the notification fd of the loaded
       filter, -1 if a notification fd has not yet been created, and
       -EINVAL if the filter context is invalid.

       The seccomp_notify_id_valid() returns 0 if the id is valid, and
       -ENOENT if it is not.

       The seccomp_notify_alloc(), seccomp_notify_receive(), and
       seccomp_notify_respond() functions return zero on success,  or
       one of the following error codes on failure:

              There was a system failure beyond the control of the
              library, check the errno value for more information.

              Internal libseccomp failure.

              The library was unable to allocate enough memory.

              The library doesn't support the particular operation.

NOTES         top

       Care should be taken to avoid two different time of check/time of
       use errors.  First, after opening any resources relevant to the
       pid for a notification (e.g.  /proc/pid/mem for reading tracee
       memory to make policy decisions), applications should call
       seccomp_notify_id_valid() to make sure that the resources the
       application has opened correspond to the right pid, i.e. that the
       pid didn't die and a different task take its place.

       Second, the classic time of check/time of use issue with seccomp
       memory should also be avoided: applications should copy any
       memory they wish to use to make decisions from the tracee into
       its own address space before applying any policy decisions, since
       a multi-threaded tracee may edit the memory at any time,
       including after it's used to make a policy decision.

       A complete example of how to avoid these two races is available
       in the Linux Kernel source tree at /samples/seccomp/user-trap.c.

AUTHOR         top

       Tycho Andersen <>

COLOPHON         top

       This page is part of the libseccomp (high-level API to the Linux
       Kernel's seccomp filter) project.  Information about the project
       can be found at ⟨⟩.  If you
       have a bug report for this manual page, see
       ⟨⟩.  This page was
       obtained from the project's upstream Git repository
       ⟨⟩ on 2020-12-18.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2020-11-17.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to                 30 May 2020       seccomp_notify_alloc(3)

Pages that refer to this page: seccomp_init(3)seccomp_rule_add(3)