x SuSE Linux 13.1-RELEASE x
x SuSE Linux 13.1-RELEASEx
seccomp_notify_alloc(3) libseccomp Documentation seccomp_notify_alloc(3)
NAME
seccomp_notify_alloc, seccomp_notify_free, seccomp_notify_receive, sec-
comp_notify_respond, seccomp_notify_id_valid, seccomp_notify_fd - Man-
age 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 al-
locates 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 re-
quest, 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 fil-
ter, -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_no-
tify_respond() functions return zero on success, or one of the follow-
ing 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 be-
fore 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
Tycho Andersen <tycho@tycho.ws>
tycho@tycho.ws 30 May 2020 seccomp_notify_alloc(3)
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