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From: ron@brl-sem.ARPA (Ron Natalie <ron>)
Newsgroups: net.bugs.4bsd
Subject: Re: 4.3 rcp can clobber a source file; does not understand host.user:file
Message-ID: <456@brl-sem.ARPA>
Date: Wed, 22-Oct-86 20:06:12 EST
Article-I.D.: brl-sem.456
Posted: Wed Oct 22 20:06:12 1986
Date-Received: Mon, 27-Oct-86 00:59:09 EST
References: <1721@emory.UUCP>
Organization: Ballistic Research Lab (BRL), APG, MD.
Lines: 25
Keywords: remote copy, bugs, file clobbering

In article <1721@emory.UUCP>, arnold@emory.UUCP (Arnold D. Robbins {EUCC}) writes:
> Subject: rcp can clobber a file; does not understand host.user:file notation
> Index:	/usr/src/bin/rcp.c 4.3BSD
> 
> Description:
> 	Secondly, rcp can clobber a file by attempting to copy it onto
> 	itself, when a "remote" file is actually a local file. See the
> 	example below. (Admittedly, this is a hole more than a "bug", but
> 	it can be a problem in many environments, particularly where there
> 	are shorthand names. E.g., we have two machines, "emoryu1" and
> 	"emoryu2", with nicknames of "u1" and "u2". I clobbered files a
> 	number of times until I learned to be more careful.)

The better solution, is what we did.
Rather than trying to assure that we are not doing a copy to the source
file, which is very difficult to get right.  We just fixed it so doing
such a copy is not destructive (albeit not very efficient either).  The
way to do this is to not do a creat first if there already exists a file
there.  Then after the copy is done, do a TRUNCATE to make the file the
right length.  This has the effect of just reading and writing all the
blocks in place.

I'll send the code diffs in the normal bug format.

-Ron