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Fix race condition in pw caused by multiple instances of pwd_mkdb being

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run at the same time.

Notes:
    The fileupdate function is still somewhat broken.  Instead of
    returning a failure code if it can't modify the original file it
    renames the .new file and continues as though nothing is wrong.
    This will cause the lock on the original file to be lost and could
    lead to a similar race condition.  I left that portion of the code
    alone since I feel that the maintainer of the code would have a
    better concept of how he wants to handle errors in that function
    than I do.

PR:		bin/6787
Submitted by:	Craig Spannring <cts@internetcds.com>
This commit is contained in:
Nate Williams 1998-07-16 17:18:25 +00:00
parent 3a4215418c
commit 73375325b1
3 changed files with 39 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
usr.sbin/pw/edgroup.c
View File

@ -26,7 +26,7 @@
#ifndef lint
static const char rcsid[] =
"$Id$";
"$Id: edgroup.c,v 1.5 1997/10/10 06:23:30 charnier Exp $";
#endif /* not lint */
#include <stdio.h>
@ -64,7 +64,7 @@ editgroups(char *name, char **groups)
int rc = 0;
int infd;
if ((infd = open(groupfile, O_RDWR | O_CREAT | O_EXLOCK, 0644)) != -1) {
if ((infd = open(groupfile, O_RDWR | O_CREAT, 0644)) != -1) {
FILE *infp;
if ((infp = fdopen(infd, "r+")) == NULL)

17
usr.sbin/pw/fileupd.c
View File

@ -26,7 +26,7 @@
#ifndef lint
static const char rcsid[] =
"$Id$";
"$Id: fileupd.c,v 1.5 1997/10/10 06:23:31 charnier Exp $";
#endif /* not lint */
#include <stdio.h>
@ -76,7 +76,7 @@ fileupdate(char const * filename, mode_t fmode, char const * newline, char const
if (pfxlen <= 1)
errno = EINVAL;
else {
int infd = open(filename, O_RDWR | O_CREAT | O_EXLOCK, fmode);
int infd = open(filename, O_RDWR | O_CREAT, fmode);
if (infd != -1) {
FILE *infp = fdopen(infd, "r+");
@ -168,9 +168,20 @@ fileupdate(char const * filename, mode_t fmode, char const * newline, char const
fputs(line, infp);
/*
* If there was a problem with copying
* we will just rename 'file.new'
* to 'file'.
* This is a gross hack, but we may have
* corrupted the original file
* Unfortunately, it will lose the inode.
* Unfortunately, it will lose the inode
* and hence the lock.
*
* The implications of this is that this invocation of pw
* won't have the file locked and concurrent copies
* of pw, vipw etc could clobber what this one is doing.
*
* It should probably just return an error instead
* of going on like nothing is wrong.
*/
if (fflush(infp) == EOF || ferror(infp))
rc = rename(file, filename) == 0;

25
usr.sbin/pw/pw.c
View File

@ -26,11 +26,12 @@
#ifndef lint
static const char rcsid[] =
"$Id$";
"$Id: pw.c,v 1.7 1997/10/10 06:23:34 charnier Exp $";
#endif /* not lint */
#include "pw.h"
#include <err.h>
#include <fcntl.h>
#include <paths.h>
#include <sys/wait.h>
@ -49,6 +50,7 @@ static struct cargs arglist;
static int getindex(const char *words[], const char *word);
static void cmdhelp(int mode, int which);
static int filelock(const char *filename);
int
@ -147,7 +149,20 @@ main(int argc, char *argv[])
* Now, let's do the common initialisation
*/
cnf = read_userconfig(getarg(&arglist, 'C') ? getarg(&arglist, 'C')->val : NULL);
ch = funcs[which] (cnf, mode, &arglist);
/*
* Be pessimistic and lock the master passowrd and group
* files right away. Keep it locked for the duration.
*/
if (-1 == filelock(_PATH_GROUP) || -1 == filelock(_PATH_MASTERPASSWD))
{
ch = EX_IOERR;
}
else
{
ch = funcs[which] (cnf, mode, &arglist);
}
/*
* If everything went ok, and we've been asked to update
@ -177,6 +192,12 @@ main(int argc, char *argv[])
return ch;
}
static int
filelock(const char *filename)
{
return open(filename, O_RDONLY | O_EXLOCK, 0);
}
static int
getindex(const char *words[], const char *word)
{