xref: /freebsd/share/man/man9/VOP_ACCESS.9 (revision 571dba6ec9f25ecf7582dc2192daf1ceea70065f)

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.\" Copyright (c) 1996 Doug Rabson
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.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
.In sys/param.h
.In sys/vnode.h
.Ft int
.Fn VOP_ACCESS "struct vnode *vp" "int mode" "struct ucred *cred" "struct thread *td"
.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 Fa vp
The vnode of the file to check.
.It Fa mode
The type of access required.
.It Fa cred
The user credentials to check.
.It Fa td
The thread 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 thread *td)
{
    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 filesystem.
     */
    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
The permission bits the file mode or the ACL do not permit the
requested access.
.El
.Sh SEE ALSO
.Xr vaccess 9 ,
.Xr vaccess_acl_posix1e 9 ,
.Xr vnode 9
.Sh AUTHORS
This manual page was written by
.An Doug Rabson .