# seccomp_notify_alloc

## NAME



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


## SYNOPSIS



           **#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



           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
           **seccomp_notify_alloc**().
    
           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



           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:
    
           **-ECANCELED**
                  There was a system failure beyond the control of the
                  library, check the _errno_ value for more information.
    
           **-EFAULT**
                  Internal libseccomp failure.
    
           **-ENOMEM**
                  The library was unable to allocate enough memory.
    
           **-EOPNOTSUPP**
                  The library doesn't support the particular operation.
    


## NOTES



           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.**
    


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