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From: guy@sun.uucp (Guy Harris)
Newsgroups: net.bugs.4bsd
Subject: "tar" gets confused when a directory appears twice on a tape
Message-ID: <5675@sun.uucp>
Date: Wed, 30-Jul-86 17:33:47 EDT
Article-I.D.: sun.5675
Posted: Wed Jul 30 17:33:47 1986
Date-Received: Thu, 31-Jul-86 21:56:09 EDT
Distribution: net
Organization: Sun Microsystems, Inc.
Lines: 81

Index:	bin/tar.c 4.3BSD

Description:
	The "directory stack" code in "tar" for setting modification
	times on directories has a loop that compares two strings, looking
	for the first place at which they differ.  However, it assumes
	that they will differ somewhere; it does not check for a terminating
	'\0'.  As such, if they do *not* differ, it runs off the end of
	the strings and keeps going until it finds two bytes that *do*
	differ.

	If the same directory appears on the tape twice, it can encounter
	two such strings that do not differ.  This means that when it
	modifies one string at the point at which it "differed" from
	the other string, it will stomp some random location in memory.
	we found it tended to happen in the middle of the variables
	containing the values of various options, so the "-m" flag magically
	turned on when extracting from a tape.
Repeat-By:
	Tell "tar" to put a directory and a subdirectory of it, both
	containing files, on a tape.  Then try extracting the contents
	of that tape.  Some of the files may not get the modification
	time set from the value on the tape.
Fix:
	Also incldues a small fix to an error message printout ('perror("")'
	does NOT print a colon before its message, so you DO need to stick
	it in the "fprintf") and a minor cleanup ("readdir" already
	eliminates empty directory slots, so there's no reason to check
	for a zero inumber).

*** /arch/4.3/usr/src/bin/tar.c	Sat Apr 26 04:35:13 1986
--- ./tar.c	Wed Jul 30 14:02:03 1986
***************
*** 512,519 ****
  			return;
  		}
  		while ((dp = readdir(dirp)) != NULL && !term) {
- 			if (dp->d_ino == 0)
- 				continue;
  			if (!strcmp(".", dp->d_name) ||
  			    !strcmp("..", dp->d_name))
  				continue;
--- 512,517 ----
***************
*** 750,756 ****
  			nread = readtbuf(&bufp, nwant);
  			if (write(ofile, bufp, (int)min(nread, bytes)) < 0) {
  				fprintf(stderr,
! 				    "tar: %s: HELP - extract write error",
  				    dblock.dbuf.name);
  				perror("");
  				done(2);
--- 748,754 ----
  			nread = readtbuf(&bufp, nwant);
  			if (write(ofile, bufp, (int)min(nread, bytes)) < 0) {
  				fprintf(stderr,
! 				    "tar: %s: HELP - extract write error: ",
  				    dblock.dbuf.name);
  				perror("");
  				done(2);
***************
*** 1358,1364 ****
  	int savndir;
  
  	/* Find common prefix */
! 	while (*p == *q) {
  		if (*p++ == '/')
  			++ndir;
  		q++;
--- 1356,1362 ----
  	int savndir;
  
  	/* Find common prefix */
! 	while (*p == *q && *p) {
  		if (*p++ == '/')
  			++ndir;
  		q++;
-- 
	Guy Harris
	{ihnp4, decvax, seismo, decwrl, ...}!sun!guy
	guy@sun.com (or guy@sun.arpa)