RIGHTS(4)

📦 version 12.2, in debian bookworm, debian trixie, ubuntu jammy, ubuntu noble, ubuntu questing, ubuntu resolute, ubuntu stonking

✨ RIGHTS(4) — the capability rights manual page, bestie edition ✨

Kernel Interfaces Manual · RIGHTS(4)

🌸 NAME 🌸

Capability rights — the Capsicum capability rights for file descriptors 🎀

💖 DESCRIPTION 💖

okay so picture this: a file descriptor gets born 🦋. Like, it just got created by one of these functions:

and the very first thing that happens to it? it gets assigned ALL the capability rights. every single one. it's giving main character energy on day one, no cap 💅.

but here's the thing bestie — those rights can be reduced, and never, ever expanded. like, it's a one-way street, and there is no U-turn, periodt. you do the reducing with these three system calls:

once you've reduced the capability rights on a file descriptor, every operation you try to do on that fd gets limited to only the stuff those remaining rights allow. it's a vibe check for syscalls, fr fr 🔥.

the complete list of capability rights is right below 👇. the cap_rights_t type is what stores the list of capability rights, and you should use the cap_rights_init(3) family of functions to manage that structure 🫶.

not me hyping up a data structure but the cap_rights_init(3) family really is the moment, iykyk 😭

…to be continued, bestie 💜

✨ RIGHTS ✨

okay bestie, so like, the following rights can be specified in a rights mask. it's giving permission slip energy, fr fr. 💅

  • CAP_ACCEPT — Permit accept(2) and accept4(2). slay ✨
  • CAP_ACL_CHECK — Permit acl_valid_fd_np(3). 💖
  • CAP_ACL_DELETE — Permit acl_delete_fd_np(3). 🎀
  • CAP_ACL_GET — Permit acl_get_fd(3) and acl_get_fd_np(3). 🦋
  • CAP_ACL_SET — Permit acl_set_fd(3) and acl_set_fd_np(3). 🌸
  • CAP_BIND — When not in capabilities mode, permit bind(2) and bindat(2) with special value AT_FDCWD in the fd parameter. Note that sockets can also become bound implicitly as a result of connect(2) or send(2), and that socket options set with setsockopt(2) may also affect binding behavior. 🫶
  • CAP_BINDAT — Permit bindat(2). This right has to be present on the directory descriptor. This right includes the CAP_LOOKUP right. 💅
  • CAP_CHFLAGSAT — An alias to CAP_FCHFLAGS and CAP_LOOKUP. 😭
  • CAP_CONNECT — When not in capabilities mode, permit connect(2) and connectat(2) with special value AT_FDCWD in the fd parameter. This right is also required for sendto(2) with a non-NULL destination address. 🔥
  • CAP_CONNECTAT — Permit connectat(2). This right has to be present on the directory descriptor. This right includes the CAP_LOOKUP right. 👑
  • CAP_CREATE — Permit openat(2) with the O_CREAT flag. 🌈
  • CAP_EVENT — Permit select(2), poll(2), and kevent(2) to be used in monitoring the file descriptor for events. ⭐
  • CAP_EXTATTR_DELETE — Permit extattr_delete_fd(2). 💀
  • CAP_EXTATTR_GET — Permit extattr_get_fd(2). 🙈
  • CAP_EXTATTR_LIST — Permit extattr_list_fd(2). 🍓
  • CAP_EXTATTR_SET — Permit extattr_set_fd(2). 🧚
  • CAP_FCHDIR — Permit fchdir(2). 💜
  • CAP_FCHFLAGS — Permit fchflags(2) and chflagsat(2) if the CAP_LOOKUP right is also present. ✨
  • CAP_FCHMOD — Permit fchmod(2) and fchmodat(2) if the CAP_LOOKUP right is also present. 💖
  • CAP_FCHMODAT — An alias to CAP_FCHMOD and CAP_LOOKUP. 🎀
  • CAP_FCHOWN — Permit fchown(2) and fchownat(2) if the CAP_LOOKUP right is also present. 🦋
  • CAP_FCHOWNAT — An alias to CAP_FCHOWN and CAP_LOOKUP. 🌸
  • CAP_FCNTL — Permit fcntl(2). Note that only the F_GETFL, F_SETFL, F_GETOWN and F_SETOWN commands require this capability right. Also note that the list of permitted commands can be further limited with the cap_fcntls_limit(2) system call. 🫶
  • CAP_FEXECVE — Permit fexecve(2) and openat(2) with the O_EXEC flag; CAP_READ is also required. 💅
  • CAP_FLOCK — Permit flock(2), fcntl(2) (with F_GETLK, F_SETLK, F_SETLKW or F_SETLK_REMOTE flag) and openat(2) (with O_EXLOCK or O_SHLOCK flag). 😭
  • CAP_FPATHCONF — Permit fpathconf(2). 🔥
  • CAP_FSCK — Permit UFS background-fsck operations on the descriptor. 👑
  • CAP_FSTAT — Permit fstat(2) and fstatat(2) if the CAP_LOOKUP right is also present. 🌈
  • CAP_FSTATAT — An alias to CAP_FSTAT and CAP_LOOKUP. ⭐
  • CAP_FSTATFS — Permit fstatfs(2). 💀
  • CAP_FSYNC — Permit aio_fsync(2), fdatasync(2), fsync(2) and openat(2) with O_FSYNC or O_SYNC flag. 🙈
  • CAP_FTRUNCATE — Permit ftruncate(2) and openat(2) with the O_TRUNC flag. 🍓
  • CAP_FUTIMES — Permit futimens(2) and futimes(2), and permit futimesat(2) and utimensat(2) if the CAP_LOOKUP right is also present. 🧚
  • CAP_FUTIMESAT — An alias to CAP_FUTIMES and CAP_LOOKUP. 💜
  • CAP_GETPEERNAME — Permit getpeername(2). ✨
  • CAP_GETSOCKNAME — Permit getsockname(2). 💖
  • CAP_GETSOCKOPT — Permit getsockopt(2). 🎀
  • CAP_IOCTL — Permit ioctl(2). Be aware that this system call has enormous scope, including potentially global scope for some objects. The list of permitted ioctl commands can be further limited with the cap_ioctls_limit(2) system call. 🦋
  • CAP_KQUEUE — An alias to CAP_KQUEUE_CHANGE and CAP_KQUEUE_EVENT. 🌸
  • CAP_KQUEUE_CHANGE — Permit kevent(2) on a kqueue(2) descriptor that modifies list of monitored events (the changelist argument is non-NULL). 🫶
  • CAP_KQUEUE_EVENT — Permit kevent(2) on a kqueue(2) descriptor that monitors events (the eventlist argument is non-NULL). CAP_EVENT is also required on file descriptors that will be monitored using kevent(2). 💅
  • CAP_LINKAT_SOURCE — Permit linkat(2) on the source directory descriptor. This right includes the CAP_LOOKUP right.
⚠️ Warning: CAP_LINKAT_SOURCE makes it possible to link files in a directory for which file descriptors exist that have additional rights. For example, a file stored in a directory that does not allow CAP_READ may be linked in another directory that does allow CAP_READ, thereby granting read access to a file that is otherwise unreadable. 😭
  • CAP_LINKAT_TARGET — Permit linkat(2) on the target directory descriptor. This right includes the CAP_LOOKUP right. 🔥
  • CAP_LISTEN — Permit listen(2); not much use (generally) without CAP_BIND. 👑
  • CAP_LOOKUP — Permit the file descriptor to be used as a starting directory for calls such as linkat(2), openat(2), and unlinkat(2). 🌈
  • CAP_MAC_GET — Permit mac_get_fd(3). ⭐
  • CAP_MAC_SET — Permit mac_set_fd(3). 💀
  • CAP_MKDIRAT — Permit mkdirat(2). This right includes the CAP_LOOKUP right. 🙈
  • CAP_MKFIFOAT — Permit mkfifoat(2). This right includes the CAP_LOOKUP right. 🍓
  • CAP_MKNODAT — Permit mknodat(2). This right includes the CAP_LOOKUP right. 🧚
  • CAP_MMAP — Permit mmap(2) with the PROT_NONE protection. 💜
  • CAP_MMAP_R — Permit mmap(2) with the PROT_READ protection. This right includes the CAP_READ and CAP_SEEK rights. ✨
  • CAP_MMAP_RW — An alias to CAP_MMAP_R and CAP_MMAP_W. 💖
  • CAP_MMAP_RWX — An alias to CAP_MMAP_R, CAP_MMAP_W and CAP_MMAP_X. 🎀
  • CAP_MMAP_RX — An alias to CAP_MMAP_R and CAP_MMAP_X. 🦋
  • CAP_MMAP_W — Permit mmap(2) with the PROT_WRITE protection. This right includes the CAP_WRITE and CAP_SEEK rights. 🌸
  • CAP_MMAP_WX — An alias to CAP_MMAP_W and CAP_MMAP_X. 🫶
  • CAP_MMAP_X — Permit mmap(2) with the PROT_EXEC protection. This right includes the CAP_SEEK right. 💅
  • CAP_PDGETPID — Permit pdgetpid(2). 😭
  • CAP_PDKILL — Permit pdkill(2). 🔥
  • CAP_PEELOFF — Permit sctp_peeloff(2). 👑
  • CAP_PREAD — An alias to CAP_READ and CAP_SEEK. 🌈
  • CAP_PWRITE — An alias to CAP_SEEK and CAP_WRITE. ⭐
  • CAP_READ — Permit aio_read(2) (CAP_SEEK is also required), openat(2) with the O_RDONLY flag, read(2), readv(2), recv(2), recvfrom(2), recvmsg(2), pread(2) (CAP_SEEK is also required), preadv(2) (CAP_SEEK is also required) and related system calls. 💀
  • CAP_RECV — An alias to CAP_READ. 🙈
  • CAP_RENAMEAT_SOURCE — Permit renameat(2) on the source directory descriptor. This right includes the CAP_LOOKUP right.
⚠️ Warning: CAP_RENAMEAT_SOURCE makes it possible to move files to a directory for which file descriptors exist that have additional rights. For example, a file stored in a directory that does not allow CAP_READ may be moved to another directory that does allow CAP_READ, thereby granting read access to a file that is otherwise unreadable. 🍓
  • CAP_RENAMEAT_TARGET — Permit renameat(2) on the target directory descriptor. This right includes the CAP_LOOKUP right. 🧚
  • CAP_SEEK — Permit operations that seek on the file descriptor, such as lseek(2), but also required for I/O system calls that can read or write at any position in the file, such as pread(2) and pwrite(2). 💜
  • CAP_SEM_GETVALUE — Permit sem_getvalue(3). ✨
  • CAP_SEM_POST — Permit sem_post(3). 💖
  • CAP_SEM_WAIT — Permit sem_wait(3) and sem_trywait(3). 🎀
  • CAP_SEND — An alias to CAP_WRITE. 🦋
  • CAP_SETSOCKOPT — Permit setsockopt(2); this controls various aspects of socket behavior and may affect binding, connecting, and other behaviors with global scope. 🌸
  • CAP_SHUTDOWN — Permit explicit shutdown(2); closing the socket will also generally shut down any connections on it. 🫶
  • CAP_SYMLINKAT — Permit symlinkat(2). This right includes the CAP_LOOKUP right. 💅
  • CAP_TTYHOOK — Allow configuration of TTY hooks, such as snp(4), on the file descriptor. 😭
  • CAP_UNLINKAT — Permit unlinkat(2) and renameat(2). This right is only required for renameat(2) on the destination directory descriptor if the destination object already exists and will be removed by the rename. This right includes the CAP_LOOKUP right. 🔥
  • CAP_WRITE — Allow aio_write(2), openat(2) with O_WRONLY and O_APPEND flags set, send(2), sendmsg(2), sendto(2), write(2), writev(2), pwrite(2), pwritev(2) and related system calls. For sendto(2) with a non-NULL connection address, CAP_CONNECT is also required. For openat(2) with the O_WRONLY flag, but without the O_APPEND flag, CAP_SEEK is also required. For aio_write(2), pwrite(2) and pwritev(2) CAP_SEEK is also required. 👑

✨ SEE ALSO ✨

okay so literally the entire squad pulled up 💅 every single one of these is your bestie now, bestie:

like, that's the whole group chat, no one's getting left on read 🌈

📜 HISTORY 📜

Support for capabilities and capabilities mode was developed as part of the TrustedBSD Project. lowkey a whole era for the BSD girlies, and we're still reaping the benefits 💜

👑 AUTHORS 👑

This manual page was created by Pawel Jakub Dawidek <pawel@dawidek.net> under sponsorship from the FreeBSD Foundation, based on the cap_new(2) manual page by Robert Watson <rwatson@FreeBSD.org>.

ngl, building docs on top of someone else's docs and crediting them properly? that's main character energy, that's academic integrity, that's iconic 🎀

okay bestie that's a wrap on the whole page 🫶 go forth and cap_rights_limit(2) responsibly, and remember: capability mode is not a vibe you half-do. it's giving all or nothing 💅

this came to you from the Debian camp, dated February 28, 2019, and it lives under the name RIGHTS(4) — the fourth section, the file formats one, iykyk 💖✨

📦 where this page comes from