CAP_GETMODE(2FREEBSD) - Linux man page online | System calls

Capability mode system calls.

September 27, 2016
CAP_ENTER(2) BSD System Calls Manual CAP_ENTER(2)


cap_enter, cap_getmode — Capability mode system calls


Standard C Library (libc, -lc)


#include <sys/capsicum.h> int cap_enter(void); int cap_getmode(u_int *modep);


cap_enter() places the current process into capability mode, a mode of execution in which processes may only issue system calls operating on file descriptors or reading limited global system state. Access to global name spaces, such as file system or IPC name spaces, is prevented. If the process is already in a capability mode sandbox, the system call is a no-op. Future process descendants created with fork(2) or pdfork(2) will be placed in capa‐ bility mode from inception. When combined with cap_rights_limit(2), cap_ioctls_limit(2), cap_fcntls_limit(2), cap_enter() may be used to create kernel-enforced sandboxes in which appropriately-crafted applications or application components may be run. cap_getmode() returns a flag indicating whether or not the process is in a capability mode sandbox. RUN-TIME SETTINGS If the kern.trap_enocap sysctl MIB is set to a non-zero value, then for any process execut‐ ing in a capability mode sandbox, any syscall which results in either an ENOTCAPABLE or ECAPMODE error also generates the synchronous SIGTRAP signal to the thread on the syscall return. On signal delivery, the si_errno member of the siginfo signal handler parameter is set to the syscall error value, and the si_code member is set to TRAP_CAP. See also the PROC_TRAPCAP_CTL and PROC_TRAPCAP_STATUS operations of the procctl(2) function for similar per-process functionality.


Creating effective process sandboxes is a tricky process that involves identifying the least possible rights required by the process and then passing those rights into the process in a safe manner. Consumers of cap_enter() should also be aware of other inherited rights, such as access to VM resources, memory contents, and other process properties that should be con‐ sidered. It is advisable to use fexecve(2) to create a runtime environment inside the sand‐ box that has as few implicitly acquired rights as possible.


The cap_enter() and cap_getmode() functions return the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error.


The cap_enter() and cap_getmode() system calls will fail if: [ENOSYS] The kernel is compiled without: options CAPABILITY_MODE The cap_getmode() system call may also return the following error: [EFAULT] Pointer modep points outside the process's allocated address space.


cap_fcntls_limit(2), cap_ioctls_limit(2), cap_rights_limit(2), procctl(2), sysctl(2), fexecve(2), cap_sandboxed(3), capsicum(4)


Support for capabilities and capabilities mode was developed as part of the TrustedBSD Project.


These functions and the capability facility were created by Robert N. M. Watson at the Uni‐ versity of Cambridge Computer Laboratory with support from a grant from Google, Inc.
BSD September 27, 2016 BSD
This manual Reference Other manuals
cap_getmode(2freebsd) referred by capsicum(4freebsd) | procenv(1)
refer to cap_enter(2freebsd) | cap_fcntls_limit(2freebsd) | cap_ioctls_limit(2freebsd) | cap_rights_limit(2freebsd) | capsicum(4freebsd) | fexecve(2freebsd) | fork(2) | pdfork(2freebsd) | procctl(2freebsd) | sysctl(2)
Download raw manual
Index BSD System Calls Manual (+360) BSD (+3984) № 2 (+877)
Go top