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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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The strategy used to maintain protected
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spooling areas is as follows:
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The spooling area is writable only by a \fIdaemon\fP user
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and \fIdaemon\fP group.
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The \fIlpr\fP program runs set-user-id to \fIroot\fP and
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set-group-id to group \fIdaemon\fP. The \fIroot\fP access permits
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reading any file required. Accessibility is verified
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with an \fIaccess\fP\|(2) call. The group ID
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is used in setting up proper ownership of files
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in the spooling area for \fIlprm\fP.
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Control files in a spooling area are made with \fIdaemon\fP
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The spooling area is writable only by \fIroot\fP and
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and the \fIdaemon\fP group.
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The \fIlpr\fP and \fIlprm\fP programs run set-user-id to user \fIdaemon\fP and
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set-group-id to group \fIdaemon\fP.
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The \fIlpc\fP and \fIlpq\fP programs run set-group-id to group \fIdaemon\fP
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to access spool files.
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Control and data files in a spooling area are made with \fIdaemon\fP
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ownership and group ownership \fIdaemon\fP. Their mode is 0660.
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This insures control files are not modified by a user
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This ensures control files are not modified by a user
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and that no user can remove files except through \fIlprm\fP.
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The spooling programs,
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\fIlpd\fP, \fIlpq\fP, and \fIlprm\fP run set-user-id to \fIroot\fP
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and set-group-id to group \fIdaemon\fP to access spool files and printers.
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The printer server, \fIlpd\fP,
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uses the same verification procedures as \fIrshd\fP\|(8C)
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in authenticating remote clients. The host on which a client
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resides must be present in the file /etc/hosts.equiv or /etc/hosts.lpd and
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the request message must come from a reserved port number.
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In practice, none of \fIlpd\fP, \fIlpq\fP, or
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\fIlprm\fP would have to run as user \fIroot\fP if remote
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spooling were not supported. In previous incarnations of
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the printer system \fIlpd\fP ran set-user-id to \fIdaemon\fP,
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set-group-id to group \fIspooling\fP, and \fIlpq\fP and \fIlprm\fP ran
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set-group-id to group \fIspooling\fP.
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The printer server, \fIlpd\fP, runs as \fIroot\fP but spends most
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of its time with the effective user-id set to \fIdaemon\fP and the
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effective group-id set to \fIdaemon\fP. As a result, spool files
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it creates belong to user and group \fIdaemon\fP. \fILpd\fP uses
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the same verification procedures as \fIrshd\fP\|(8) in authenticating
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remote clients. The host on which a client resides must be present
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in the file /etc/hosts.equiv or /etc/hosts.lpd and the request
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message must come from a reserved port number.
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SMM.doc/3.t
