freebsd-dev/usr.sbin/pw/fileupd.c
Nate Williams 73375325b1 Fix race condition in pw caused by multiple instances of pwd_mkdb being
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>
1998-07-16 17:18:25 +00:00

203 lines
6.1 KiB
C

/*-
* Copyright (C) 1996
* David L. Nugent. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY DAVID L. NUGENT AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL DAVID L. NUGENT OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#ifndef lint
static const char rcsid[] =
"$Id: fileupd.c,v 1.5 1997/10/10 06:23:31 charnier Exp $";
#endif /* not lint */
#include <stdio.h>
#include <fcntl.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/param.h>
#include <errno.h>
#include <unistd.h>
#include "pwupd.h"
int
extendline(char **buf, int * buflen, int needed)
{
if (needed > *buflen) {
char *tmp = realloc(*buf, needed);
if (tmp == NULL)
return -1;
*buf = tmp;
*buflen = needed;
}
return *buflen;
}
int
extendarray(char ***buf, int * buflen, int needed)
{
if (needed > *buflen) {
char **tmp = realloc(*buf, needed * sizeof(char *));
if (tmp == NULL)
return -1;
*buf = tmp;
*buflen = needed;
}
return *buflen;
}
int
fileupdate(char const * filename, mode_t fmode, char const * newline, char const * prefix, int pfxlen, int updmode)
{
int rc = 0;
if (pfxlen <= 1)
errno = EINVAL;
else {
int infd = open(filename, O_RDWR | O_CREAT, fmode);
if (infd != -1) {
FILE *infp = fdopen(infd, "r+");
if (infp == NULL)
close(infd);
else {
int outfd;
char file[MAXPATHLEN];
strcpy(file, filename);
strcat(file, ".new");
outfd = open(file, O_RDWR | O_CREAT | O_TRUNC | O_EXLOCK, fmode);
if (outfd != -1) {
FILE *outfp = fdopen(outfd, "w+");
if (outfp == NULL)
close(outfd);
else {
int updated = UPD_CREATE;
int linesize = PWBUFSZ;
char *line = malloc(linesize);
nextline:
while (fgets(line, linesize, infp) != NULL) {
char *p = strchr(line, '\n');
while ((p = strchr(line, '\n')) == NULL) {
int l;
if (extendline(&line, &linesize, linesize + PWBUFSZ) == -1) {
int ch;
fputs(line, outfp);
while ((ch = fgetc(infp)) != EOF) {
fputc(ch, outfp);
if (ch == '\n')
break;
}
goto nextline;
}
l = strlen(line);
if (fgets(line + l, linesize - l, infp) == NULL)
break;
}
if (*line != '#' && *line != '\n') {
if (!updated && strncmp(line, prefix, pfxlen) == 0) {
updated = updmode == UPD_REPLACE ? UPD_REPLACE : UPD_DELETE;
/*
* Only actually write changes if updating
*/
if (updmode == UPD_REPLACE)
strcpy(line, newline);
else if (updmode == UPD_DELETE)
continue;
}
}
fputs(line, outfp);
}
/*
* Now, we need to decide what to do: If we are in
* update mode, and no record was updated, then error If
* we are in insert mode, and record already exists,
* then error
*/
if (updmode != updated)
errno = (updmode == UPD_CREATE) ? EEXIST : ENOENT;
else {
/*
* If adding a new record, append it to the end
*/
if (updmode == UPD_CREATE)
fputs(newline, outfp);
/*
* Flush the file and check for the result
*/
rc = fflush(outfp) != EOF;
if (rc) {
/*
* Copy data back into the
* original file and truncate
*/
rewind(infp);
rewind(outfp);
while (fgets(line, linesize, outfp) != NULL)
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
* 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;
else
ftruncate(infd, ftell(infp));
}
}
free(line);
fclose(outfp);
}
remove(file);
}
fclose(infp);
}
}
}
return rc;
}