Path: utzoo!utgpu!attcan!uunet!lll-winken!lll-tis!ames!haven!adm!xadmx!becker@trantor.harris-atd.com
From: becker@trantor.harris-atd.com (Don Becker)
Newsgroups: comp.unix.wizards
Subject: syslog(), openlog(), bug in syslog.c patch
Message-ID: <17826@adm.BRL.MIL>
Date: 15 Dec 88 22:43:32 GMT
Sender: news@adm.BRL.MIL
Lines: 58


I changed our version of ftpd to do logging, and also ran into the
syslog() lossage over chroot().  At the bottom of my message is a bug
report, to clarify the issue for newcomers.

I installed a fix similar to the one suggested by Tad Guy
<tadguy@cs.odu.edu>.  A quick look at his change suggests that he
doesn't deal with the case where a connect() is not done -- he always
has syslog() do a send() rather than a sendto() to the socket.  Recall that,
as the manual states,
	Send may be used only when the  socket  is  in  a  connected
	state, while sendto and sendmsg may be used at any time.
Thus some provision should be made (a flag variable) to indicate the
connect() has not been done, and that a sendto() should be used instead.

Making a connection is the Right Thing, and should be default.  It
should be more efficient than doing namei() on "/dev/log" each time
inside of sendto, but I suspect that it isn't.

A potential fix is to record the absolute pathname in the kernel table
whenever a UNIX domain socket is made, however this might not be
considered a "simple fix" by most people.

Bug report _________________

Bug:
	syslog() fails silently after/across chroot() calls.
	sendto() has an undocumented error value (ENOENT) on unix
	domain sockets

Cause:
	syslog() uses UNIX domain datagrams to communicate, and for each
	sendto() the unix domain socket address is looked up again.  When
	a chroot() is done the AF_UNIX address "/dev/log" is invalid.

Fix:
	At the very least this behavior should be documented.

	An additional flag to openlog could specify Internet domain
	instead of UNIX domain datagrams.  Syslogd already listens there
	for log messages from other machines.

	Unix domain sockets could record the absolute pathname rather than
	just the pathname relative to the current root directory.

Questions and comments:
	It is clear why UNIX domain datagrams have this behavior, but it
	means they have to do the namei() lookup on the address (pathname)
	for every datagram, doesn't it?

	At a higher level, openlog() implies that something analogous to
	an open happens, and open files remain valid across chroot() calls.
	Even in looking at the source to syslog() it isn't clear that the
	file descriptor for the socket could become invalid after a chroot().
	Pity the sites without source licenses.
--
Donald Becker			Advanced Technology Department
becker@trantor.harris-atd.com	Government Systems Sector
(407) 729-7303			Harris Corporation, Melbourne, FL. 32905