|CAP_ENTER(2)||System Calls Manual||CAP_ENTER(2)|
LIBRARY¶Standard C Library (libc, -lc)
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 capability mode from inception.
When combined with cap_rights_limit(2),
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_enotcapsysctl MIB is set to a non-zero value, then for any process executing in a capability mode sandbox, any syscall which results in either an
ECAPMODEerror also generates the synchronous
SIGTRAPsignal 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
See also the
PROC_TRAPCAP_STATUS operations of the
procctl(2) function for similar per-process
CAVEAT¶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 considered. It is advisable to use fexecve(2) to create a runtime environment inside the sandbox that has as few implicitly acquired rights as possible.
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.
When the process is in capability mode,
cap_getmode() sets the flag to a non-zero value. A
zero value means the process is not in capability mode.
cap_getmode() system calls will fail if:
- The kernel is compiled without:
cap_getmode() system call may also
return the following error:
- Pointer modep points outside the process's allocated address space.
SEE ALSO¶cap_fcntls_limit(2), cap_ioctls_limit(2), cap_rights_limit(2), fexecve(2), procctl(2), cap_sandboxed(3), capsicum(4), sysctl(9)
HISTORY¶Support for capabilities and capabilities mode was developed as part of the TrustedBSD Project.
AUTHORS¶These functions and the capability facility were created by Robert N. M. Watson at the University of Cambridge Computer Laboratory with support from a grant from Google, Inc.
|May 23, 2017||Linux 4.19.0-10-amd64|