freebsd-skq/share/man/man9/VOP_ACCESS.9

.\" -*- nroff -*-
.\" -*- nroff -*-
.\"
.\" Copyright (c) 1996 Doug Rabson
.\"
.\" All rights reserved.
.\"
.\" This program is free software.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR
.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT,
.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
.\" $FreeBSD$
.\"
.Dd July 24, 1996
.Os
.Dt VOP_ACCESS 9
.Sh NAME
.Nm VOP_ACCESS
.Nd check access permissions of a file or Unix domain socket
.Sh SYNOPSIS
.Fd #include <sys/param.h>
.Fd #include <sys/vnode.h>
.Ft int
.Fn VOP_ACCESS "struct vnode *vp" "int mode" "struct ucred *cred" "struct proc *p"
.Sh DESCRIPTION
This entry point checks the access permissions of the file against the
given credentials.
.Pp
Its arguments are:
.Bl -tag -width mode
.It Ar vp
the vnode of the file to check
.It Ar mode
the type of access required
.It Ar cred
the user credentials to check
.It Ar p
the process which is checking
.El
.Pp
The
.Fa mode
is a mask which can contain
.Dv VREAD ,
.Dv VWRITE or
.Dv VEXEC.
.Sh LOCKS
The vnode will be locked on entry and should remain locked on return.
.Sh RETURN VALUES
If the file is accessible in the specified way, then zero is returned,
otherwise an appropriate error code is returned.
.Sh PSEUDOCODE
.Bd -literal
int
vop_access(struct vnode *vp, int mode, struct ucred *cred, struct proc *p)
{
    int error;

    /*
     * Disallow write attempts on read-only file systems;
     * unless the file is a socket, fifo, or a block or
     * character device resident on the file system.
     */
    if (mode & VWRITE) {
	switch (vp->v_type) {
	case VDIR:
	case VLNK:
	case VREG:
	    if (vp->v_mount->mnt_flag & MNT_RDONLY)
		return EROFS;

	    break;
	}
    }

    /* If immutable bit set, nobody gets to write it. */
    if ((mode & VWRITE) && vp has immutable bit set)
	return EPERM;

    /* Otherwise, user id 0 always gets access. */
    if (cred->cr_uid == 0)
	return 0;

    mask = 0;

    /* Otherwise, check the owner. */
    if (cred->cr_uid == owner of vp) {
	if (mode & VEXEC)
	    mask |= S_IXUSR;
	if (mode & VREAD)
	    mask |= S_IRUSR;
	if (mode & VWRITE)
	    mask |= S_IWUSR;
	return (((mode of vp) & mask) == mask ? 0 : EACCES);
    }

    /* Otherwise, check the groups. */
    for (i = 0, gp = cred->cr_groups; i < cred->cr_ngroups; i++, gp++)
	if (group of vp == *gp) {
	    if (mode & VEXEC)
		mask |= S_IXGRP;
	    if (mode & VREAD)
		mask |= S_IRGRP;
	    if (mode & VWRITE)
		mask |= S_IWGRP;
	    return (((mode of vp) & mask) == mask ? 0 : EACCES);
	}
    
    /* Otherwise, check everyone else. */
    if (mode & VEXEC)
	mask |= S_IXOTH;
    if (mode & VREAD)
	mask |= S_IROTH;
    if (mode & VWRITE)
	mask |= S_IWOTH;
    return (((mode of vp) & mask) == mask ? 0 : EACCES);
}
.Ed
.Sh ERRORS
.Bl -tag -width Er
.It Bq Er EPERM
An attempt was made to change an immutable file
.It Bq Er EACCES
Permission denied
.El
.Sh SEE ALSO
.Xr vnode 9
.Sh AUTHORS
This man page was written by
.An Doug Rabson .