Package: release.debian.org Severity: normal User: release.debian....@packages.debian.org Usertags: tpu
Hi, I prepared a tpu update for dnsmasq to isolate the fix for this problem. It would not be appropriate for me to clear this for upload myself; please could someone review and approve it. Debdiff attached, versioned 2.62-3+deb70u1. (Ignore the changelog.rej noise, it will not be in the upload.) Maintainer: this is notice of intent to NMU this fix in to wheezy, so I will delay by two days to give you chance to object. Thanks, -- Jonathan Wiltshire j...@debian.org Debian Developer http://people.debian.org/~jmw 4096R: 0xD3524C51 / 0A55 B7C5 1223 3942 86EC 74C3 5394 479D D352 4C51 <directhex> i have six years of solaris sysadmin experience, from 8->10. i am well qualified to say it is made from bonghits layered on top of bonghits
diff -u dnsmasq-2.62/debian/changelog dnsmasq-2.62/debian/changelog
--- dnsmasq-2.62/debian/changelog
+++ dnsmasq-2.62/debian/changelog
@@ -1,3 +1,11 @@
+dnsmasq (2.62-3+deb70u1) testing-proposed-updates; urgency=low
+
+ * Non-maintainer upload.
+ * Backport fix for symlink attacks from 2.63-4
+ (Closes: #686484)
+
+ -- Jonathan Wiltshire <j...@debian.org> Sun, 10 Feb 2013 21:07:17 +0000
+
dnsmasq (2.62-3) unstable; urgency=low
* Do resolvconf and /etc/default startup logic when
only in patch2:
unchanged:
--- dnsmasq-2.62.orig/src/dnsmasq.c
+++ dnsmasq-2.62/src/dnsmasq.c
@@ -371,15 +371,48 @@
/* write pidfile _after_ forking ! */
if (daemon->runfile)
{
- FILE *pidfile;
+ int fd, err = 0;
+
+ sprintf(daemon->namebuff, "%d\n", (int) getpid());
+
+ /* Explanation: Some installations of dnsmasq (eg Debian/Ubuntu) locate the pid-file
+ in a directory which is writable by the non-privileged user that dnsmasq runs as. This
+ allows the daemon to delete the file as part of its shutdown. This is a security hole to the
+ extent that an attacker running as the unprivileged user could replace the pidfile with a
+ symlink, and have the target of that symlink overwritten as root next time dnsmasq starts.
+
+ The folowing code first deletes any existing file, and then opens it with the O_EXCL flag,
+ ensuring that the open() fails should there be any existing file (because the unlink() failed,
+ or an attacker exploited the race between unlink() and open()). This ensures that no symlink
+ attack can succeed.
+
+ Any compromise of the non-privileged user still theoretically allows the pid-file to be
+ replaced whilst dnsmasq is running. The worst that could allow is that the usual
+ "shutdown dnsmasq" shell command could be tricked into stopping any other process.
+
+ Note that if dnsmasq is started as non-root (eg for testing) it silently ignores
+ failure to write the pid-file.
+ */
+
+ unlink(daemon->runfile);
- /* only complain if started as root */
- if ((pidfile = fopen(daemon->runfile, "w")))
+ if ((fd = open(daemon->runfile, O_WRONLY|O_CREAT|O_TRUNC|O_EXCL, S_IWUSR|S_IRUSR|S_IRGRP|S_IROTH)) == -1)
{
- fprintf(pidfile, "%d\n", (int) getpid());
- fclose(pidfile);
+ /* only complain if started as root */
+ if (getuid() == 0)
+ err = 1;
}
- else if (getuid() == 0)
+ else
+ {
+ if (!read_write(fd, (unsigned char *)daemon->namebuff, strlen(daemon->namebuff), 0))
+ err = 1;
+
+ while (!err && close(fd) == -1)
+ if (!retry_send())
+ err = 1;
+ }
+
+ if (err)
{
send_event(err_pipe[1], EVENT_PIDFILE, errno, daemon->runfile);
_exit(0);
only in patch2:
unchanged:
--- dnsmasq-2.62.orig/debian/changelog.rej
+++ dnsmasq-2.62/debian/changelog.rej
@@ -0,0 +1,12 @@
+--- debian/changelog
++++ debian/changelog
+@@ -1,3 +1,9 @@
++dnsmasq (2.63-4) unstable; urgency=low
++
++ * Make pid-file creation immune to symlink attacks. (closes: #686484)
++
++ -- Simon Kelley <si...@thekelleys.org.uk> Fri, 21 Sep 2012 17:16:34 +0000
++
+ dnsmasq (2.63-3) unstable; urgency=low
+
+ * Move adduser dependency to dnsmasq-base. (closes: #686694)
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