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Path: utzoo!mnetor!seismo!umcp-cs!chris
From: chris@umcp-cs.UUCP (Chris Torek)
Newsgroups: net.bugs.4bsd
Subject: Re: possible truncated /etc/passwd file
Message-ID: <3480@umcp-cs.UUCP>
Date: Wed, 17-Sep-86 09:35:46 EDT
Article-I.D.: umcp-cs.3480
Posted: Wed Sep 17 09:35:46 1986
Date-Received: Fri, 19-Sep-86 21:19:12 EDT
References: <185@uvicctr.UUCP>
Distribution: net
Organization: Computer Sci. Dept, U of Maryland, College Park, MD
Lines: 30

In article <185@uvicctr.UUCP> gduncan@uvicctr.UUCP (Gary Duncan) writes:
>Description:
>	the passwd program ... works by creating a temporary copy of the
>	updated passwd file by opening /etc/ptmp in exclusive-use mode then
>	copying and modifying entries from the original.  No problem so far.
>	The program then:
>		1. renames the temporary file to /etc/passwd
>		2. closes the stream pointer for the file.
>	Unfortunately the exclusive-use mode is lost on rename before the
>	stream buffers have been flushed. ...
>Fix:
>	Add a fflush(tf) immediately before the rename to flush the buffers.
>
>  	endpwent();
>+ 	fflush(tf);
>  	if (rename(temp, passwd) < 0) {

It would also be a very good idea to check for ferror(tf), in case
the root file system is full.  Make that:

	endpwent();
	(void) fflush(tf);
	if (ferror(tf))
		/* do something */

This, too, is quite unlikely, but could have drastic consequences.
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 1516)
UUCP:	seismo!umcp-cs!chris
CSNet:	chris@umcp-cs		ARPA:	chris@mimsy.umd.edu