Provide a man page for VOP_SETLABEL(9).
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share/man/man9/VOP_SETLABEL.9
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share/man/man9/VOP_SETLABEL.9
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.\"-
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.\" Copyright (c) 2021 Robert N. M. Watson
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" $FreeBSD$
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.\"
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.Dd February 27, 2021
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.Dt VOP_SETLABEL 9
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.Os
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.Sh NAME
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.Nm VOP_SETLABEL
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.Nd persistently store an updated MAC label on a vnode
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.Sh SYNOPSIS
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.In sys/param.h
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.In sys/vnode.h
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.In security/mac.h
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.Ft int
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.Fn VOP_SETLABEL "struct vnode *vp" "label *label"
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.Sh DESCRIPTION
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This vnode call is made by
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.Xr mac 9
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file relabeling operation has been authorized, and the filesystem must now be
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updated.
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.Ss Single-Label vs. Multi-Label Filesystems
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Filesystems that do not implement per-file labels -- known as single-label
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filesystems -- can simply leave the
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.Xr vnode 9
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operation undefined.
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These filesystems must not set the
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.Dv MNT_MULTLABEL
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flag in their
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.Vt struct mount .
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.Pp
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Filesystems that do implement per-vnode label storage -- known as multi-label
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filesystems -- will set the
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.Dv MNT_MULTILABEL
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flag in their
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.Vt struct mount .
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The UFS filesystem uses a superblock flag to persisently configure whether a
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specific filesystem implements a label for each
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.Xr vnode 9 ,
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and then keys various behaviors on whether that flag is set.
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.Ss Extended Attributes
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If the filesystem implements extended attributes, then the MAC Framework's
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.Fn vop_stdsetlabel_ea
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function can be used, and maps operations into a series of
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.Xr VOP_OPENEXTATTR 9 ,
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.Xr VOP_WRITEEXTATTR 9 ,
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and
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.Xr VOP_CLOSEEXTATTR 9 .
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.Pp
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Filesystems will also need to call
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.Fn mac_vnode_create_extattr
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when a new filesystem object is created, so that suitable extended attributes
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can be written out, and
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.Fn mac_vnode_associate_extattr
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when a
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.Xr vnode 9
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is associated with a filesystem object for the first time.
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These utility functions use
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.Xr VOP_OPENEXTATTR 9 ,
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.Xr VOP_READEXTATTR 9 ,
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.Xr VOP_WRITEEXTATTR 9 ,
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and
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.Xr VOP_CLOSEEXTATTR 9
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as required.
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.Pp
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.Ss Locking and Crash Safety
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In all cases, it is important that exclusive
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.Xr vnode 9
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locks be held to prevent concurrent access when a MAC label may not yet be
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initialized.
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It is also important that operations are ordered so that a system crash does
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not leave a file improperly labeled.
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For example, the extended attribute for a newly created file must be written
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to disk before the file is linked by its parent directory, so that there is
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no opportunity for a crash to lead to an unlabeled file.
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.Sh LOCKS
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The vnode will be locked on entry and should remain locked on return.
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.Sh RETURN VALUES
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If the MAC label is successfully set, then zero is returned.
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Otherwise, an appropriate error code is returned.
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.Sh ERRORS
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.Bl -tag -width Er
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.It Bq Er EOPNOTSUPP
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The file system does not support
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.Fn VOP_SETLABEL .
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.It Bq Er ENOSPC
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The file system is out of space.
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.It Bq Er EROFS
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The file system is read-only.
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.El
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.Pp
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Depending on the underlying implementation of
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.Fn VOP_SETLABEL ,
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other errors may also be possible.
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.Sh SEE ALSO
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.Xr VOP_CLOSEEXTATTR 9 ,
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.Xr VOP_OPENEXTATTR 9 ,
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.Xr VOP_READEXTATTR 9 ,
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.Xr VOP_WRITEXTATTR 9 ,
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.Xr mac 9 ,
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.Xr mount 9 ,
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.Xr vnode 9 ,
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.Sh AUTHORS
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This manual page was written by
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.An Robert Watson .
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