Date: Mon, 24 Jun 2002 23:00:06 -0700 (PDT) From: Paul Herman <pherman@frenchfries.net> To: freebsd-bugs@FreeBSD.org Subject: Re: bin/38676 change request for pw command Message-ID: <200206250600.g5P606q08404@freefall.freebsd.org>
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The following reply was made to PR bin/38676; it has been noted by GNATS.
From: Paul Herman <pherman@frenchfries.net>
To: FreeBSD-gnats-submit@FreeBSD.ORG
Cc: Takumi ISHII <takishii@xephion.ne.jp>,
"Geoffrey C. Speicher" <geoff@sea-incorporated.com>,
"Matthew D. Fuller" <fullermd@over-yonder.net>
Subject: Re: bin/38676 change request for pw command
Date: Mon, 24 Jun 2002 22:52:50 -0700 (PDT)
Here is an better version of the patch in bin/23501. In addition
to the advisory lock, link counts are checked to avoid any
unlink/rename issues. This has been tested by myself and seems to
also fix the problem.
The topic of HOW to best fix this bug has recently been hashed out
a bit on -hackers and -stable. Matthew Fuller proposed an
alternate fix by using a giant lock in /var/run/, so the jury is
still out on the best way to solve the problem.
I'll let Matthew speak for himself, but I feel that the either the
patch in bin/23501 or the following improved patch is the best way
to solve the problem. Opinions in the audit-trail are surely to
follow. :-)
-Paul.
Index: edgroup.c
===================================================================
RCS file: /u02/ncvs/src/usr.sbin/pw/edgroup.c,v
retrieving revision 1.8
diff -u -r1.8 edgroup.c
--- edgroup.c 28 Aug 1999 01:19:16 -0000 1.8
+++ edgroup.c 25 Jun 2002 05:27:49 -0000
@@ -68,7 +68,26 @@
strcpy(grouptmp, groupfile);
strcat(grouptmp, ".new");
- if ((infd = open(groupfile, O_RDWR | O_CREAT, 0644)) != -1) {
+ /*
+ * Open and lock the original group file. We check the link count
+ * in order to avoid any link/unlink/remove race.
+ */
+ for (;;) {
+ struct stat st;
+
+ infd = open(groupfile, O_RDWR | O_CREAT | O_EXLOCK, 0644);
+ if (infd == -1)
+ break;
+ if (fstat(infd, &st) < 0) {
+ close(infd);
+ return -1;
+ }
+ if (st.st_nlink == 1)
+ break;
+ close(infd);
+ }
+
+ if (infd != -1) {
FILE *infp;
if ((infp = fdopen(infd, "r+")) == NULL)
Index: fileupd.c
===================================================================
RCS file: /u02/ncvs/src/usr.sbin/pw/fileupd.c,v
retrieving revision 1.9
diff -u -r1.9 fileupd.c
--- fileupd.c 26 Oct 1999 04:27:13 -0000 1.9
+++ fileupd.c 25 Jun 2002 04:15:08 -0000
@@ -76,8 +76,25 @@
if (pfxlen <= 1)
rc = EINVAL;
else {
- int infd = open(filename, O_RDWR | O_CREAT, fmode);
-
+ /*
+ * Open and lock the original file. We check the link count
+ * in order to avoid any link/unlink/rename race.
+ */
+ int infd;
+ for (;;) {
+ struct stat st;
+ infd = open(filename, O_RDWR | O_CREAT | O_EXLOCK, fmode);
+ if (infd == -1)
+ break;
+ if (fstat(infd, &st) < 0) {
+ rc = errno;
+ close(infd);
+ return rc;
+ }
+ if (st.st_nlink == 1)
+ break;
+ close(infd);
+ }
if (infd == -1)
rc = errno;
else {
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