avahi: fix CVE-2021-3468

A flaw was found in avahi in versions 0.6 up to 0.8. The event used
to signal the termination of the client connection on the avahi Unix
socket is not correctly handled in the client_work function,
allowing a local attacker to trigger an infinite loop. The highest
threat from this vulnerability is to the availability of the avahi
service, which becomes unresponsive after this flaw is triggered.

https://nvd.nist.gov/vuln/detail/CVE-2021-3468
CVE: CVE-2021-3468

(From OE-Core rev: 7ca7aeb7c703bfa22c9f128849e11b62f93d81b5)

Signed-off-by: Steve Sakoman <steve@sakoman.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

2 files changed, 43 insertions, 0 deletions

diff --git a/meta/recipes-connectivity/avahi/avahi.inc b/meta/recipes-connectivity/avahi/avahi.inc
index 6acedb5412..25bb41b738 100644
--- a/meta/recipes-connectivity/avahi/avahi.inc
+++ b/meta/recipes-connectivity/avahi/avahi.inc
@@ -21,6 +21,7 @@ LIC_FILES_CHKSUM = "file://LICENSE;md5=2d5025d4aa3495befef8f17206a5b0a1 \
 
 SRC_URI = "https://github.com/lathiat/avahi/releases/download/v${PV}/avahi-${PV}.tar.gz \
            file://fix-CVE-2017-6519.patch \
+           file://CVE-2021-3468.patch \
            "
 
 UPSTREAM_CHECK_URI = "https://github.com/lathiat/avahi/releases/"
diff --git a/meta/recipes-connectivity/avahi/files/CVE-2021-3468.patch b/meta/recipes-connectivity/avahi/files/CVE-2021-3468.patch
new file mode 100644
index 0000000000..638a1f6071
--- /dev/null
+++ b/meta/recipes-connectivity/avahi/files/CVE-2021-3468.patch
@@ -0,0 +1,42 @@
+From 447affe29991ee99c6b9732fc5f2c1048a611d3b Mon Sep 17 00:00:00 2001
+From: Riccardo Schirone <sirmy15@gmail.com>
+Date: Fri, 26 Mar 2021 11:50:24 +0100
+Subject: [PATCH] Avoid infinite-loop in avahi-daemon by handling HUP event in
+ client_work
+
+If a client fills the input buffer, client_work() disables the
+AVAHI_WATCH_IN event, thus preventing the function from executing the
+`read` syscall the next times it is called. However, if the client then
+terminates the connection, the socket file descriptor receives a HUP
+event, which is not handled, thus the kernel keeps marking the HUP event
+as occurring. While iterating over the file descriptors that triggered
+an event, the client file descriptor will keep having the HUP event and
+the client_work() function is always called with AVAHI_WATCH_HUP but
+without nothing being done, thus entering an infinite loop.
+
+See https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=984938
+
+Upstream-Status: Backport
+CVE: CVE-2021-3468
+Signed-off-by: Steve Sakoman <steve@sakoman.com>
+
+---
+ avahi-daemon/simple-protocol.c | 5 +++++
+ 1 file changed, 5 insertions(+)
+
+diff --git a/avahi-daemon/simple-protocol.c b/avahi-daemon/simple-protocol.c
+index 3e0ebb11..6c0274d6 100644
+--- a/avahi-daemon/simple-protocol.c
++++ b/avahi-daemon/simple-protocol.c
+@@ -424,6 +424,11 @@ static void client_work(AvahiWatch *watch, AVAHI_GCC_UNUSED int fd, AvahiWatchEv
+         }
+     }
+ 
++    if (events & AVAHI_WATCH_HUP) {
++        client_free(c);
++        return;
++    }
++
+     c->server->poll_api->watch_update(
+         watch,
+         (c->outbuf_length > 0 ? AVAHI_WATCH_OUT : 0) |