From 48d745db7fd554fc33e96ec86d3675ebd530bb8e Mon Sep 17 00:00:00 2001
From: Michal Sekletar <msekleta@redhat.com>
Date: Mon, 23 Oct 2023 13:38:35 +0200
Subject: [PATCH] avahi: core: extract host name using avahi_unescape_label()

Previously we could create invalid escape sequence when we split the
string on dot. For example, from valid host name "foo\\.bar" we have
created invalid name "foo\\" and tried to set that as the host name
which crashed the daemon.

Fixes #453

Upstream-Status: Backport [https://github.com/lathiat/avahi/commit/894f085f402e023a98cbb6f5a3d117bd88d93b09]
CVE: CVE-2023-38471

Signed-off-by: Meenali Gupta <meenali.gupta@windriver.com>
---
 avahi-core/server.c | 27 +++++++++++++++++++++------
 1 file changed, 21 insertions(+), 6 deletions(-)

diff --git a/avahi-core/server.c b/avahi-core/server.c
index e507750..40f1d68 100644
--- a/avahi-core/server.c
+++ b/avahi-core/server.c
@@ -1295,7 +1295,11 @@ static void update_fqdn(AvahiServer *s) {
 }

 int avahi_server_set_host_name(AvahiServer *s, const char *host_name) {
-    char *hn = NULL;
+    char label_escaped[AVAHI_LABEL_MAX*4+1];
+    char label[AVAHI_LABEL_MAX];
+    char *hn = NULL, *h;
+    size_t len;
+
     assert(s);

     AVAHI_CHECK_VALIDITY(s, !host_name || avahi_is_valid_host_name(host_name), AVAHI_ERR_INVALID_HOST_NAME);
@@ -1305,17 +1309,28 @@ int avahi_server_set_host_name(AvahiServer *s, const char *host_name) {
     else
         hn = avahi_normalize_name_strdup(host_name);

-    hn[strcspn(hn, ".")] = 0;
+    h = hn;
+    if (!avahi_unescape_label((const char **)&hn, label, sizeof(label))) {
+        avahi_free(h);
+        return AVAHI_ERR_INVALID_HOST_NAME;
+    }
+
+    avahi_free(h);
+
+    h = label_escaped;
+    len = sizeof(label_escaped);
+    if (!avahi_escape_label(label, strlen(label), &h, &len))
+        return AVAHI_ERR_INVALID_HOST_NAME;

-    if (avahi_domain_equal(s->host_name, hn) && s->state != AVAHI_SERVER_COLLISION) {
-        avahi_free(hn);
+    if (avahi_domain_equal(s->host_name, label_escaped) && s->state != AVAHI_SERVER_COLLISION)
         return avahi_server_set_errno(s, AVAHI_ERR_NO_CHANGE);
-    }

     withdraw_host_rrs(s);

     avahi_free(s->host_name);
-    s->host_name = hn;
+    s->host_name = avahi_strdup(label_escaped);
+    if (!s->host_name)
+        return AVAHI_ERR_NO_MEMORY;

     update_fqdn(s);

--
2.40.0