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.Dd April 27, 2024 .Dt CAP_RIGHTS_LIMIT 2 .Os .Sh NAME .Nm cap_rights_limit .Nd limit capability rights .Sh LIBRARY .Lb libc .Sh SYNOPSIS n sys/capsicum.h .Ft int .Fn cap_rights_limit "int fd" "const cap_rights_t *rights" .Sh DESCRIPTION When a file descriptor is created by a function such as .Xr fhopen 2 , .Xr kqueue 2 , .Xr mq_open 2 , .Xr open 2 , .Xr pdfork 2 , .Xr pipe 2 , .Xr shm_open 2 , .Xr socket 2 or .Xr socketpair 2 , it is assigned all capability rights; for .Xr accept 2 , .Xr accept4 2 or .Xr openat 2 , it inherits capability rights from the "parent" file descriptor. Those rights can be reduced (but never expanded) by using the .Fn cap_rights_limit system call. Once capability rights are reduced, operations on the file descriptor will be limited to those permitted by .Fa rights .
p The .Fa rights argument should be prepared using .Xr cap_rights_init 3 family of functions.
p Capability rights assigned to a file descriptor can be obtained with the .Xr cap_rights_get 3 function.
p The complete list of the capability rights can be found in the .Xr rights 4 manual page. .Sh RETURN VALUES .Rv -std .Sh EXAMPLES The following example demonstrates how to limit file descriptor capability rights to allow reading only. d -literal cap_rights_t setrights; char buf[1]; int fd; fd = open("/tmp/foo", O_RDWR); if (fd < 0) err(1, "open() failed"); if (cap_enter() < 0) err(1, "cap_enter() failed"); cap_rights_init(&setrights, CAP_READ); if (cap_rights_limit(fd, &setrights) < 0) err(1, "cap_rights_limit() failed"); buf[0] = 'X'; if (write(fd, buf, sizeof(buf)) > 0) errx(1, "write() succeeded!"); if (read(fd, buf, sizeof(buf)) < 0) err(1, "read() failed"); .Ed .Sh ERRORS .Fn cap_rights_limit succeeds unless: l -tag -width Er t Bq Er EBADF The .Fa fd argument is not a valid active descriptor. t Bq Er EINVAL An invalid right has been requested in .Fa rights . t Bq Er ENOSYS The running kernel was compiled without .Cd "options CAPABILITY_MODE" . t Bq Er ENOTCAPABLE The .Fa rights argument contains capability rights not present for the given file descriptor. Capability rights list can only be reduced, never expanded. .El .Sh SEE ALSO .Xr accept 2 , .Xr accept4 2 , .Xr cap_enter 2 , .Xr fhopen 2 , .Xr kqueue 2 , .Xr mq_open 2 , .Xr open 2 , .Xr openat 2 , .Xr pdfork 2 , .Xr pipe 2 , .Xr read 2 , .Xr shm_open 2 , .Xr socket 2 , .Xr socketpair 2 , .Xr write 2 , .Xr cap_rights_get 3 , .Xr cap_rights_init 3 , .Xr err 3 , .Xr capsicum 4 , .Xr rights 4 .Sh HISTORY The .Fn cap_rights_limit function first appeared in .Fx 8.3 . Support for capabilities and capabilities mode was developed as part of the .Tn TrustedBSD Project. .Sh AUTHORS This function was created by .An Pawel Jakub Dawidek Aq Mt pawel@dawidek.net under sponsorship of the FreeBSD Foundation.