From 894f085f402e023a98cbb6f5a3d117bd88d93b09 Mon Sep 17 00:00:00 2001
From: Michal Sekletar <[email protected]>
Date: Mon, 23 Oct 2023 13:38:35 +0200
Subject: [PATCH] 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

CVE-2023-38471

Reference:https://github.com/lathiat/avahi/commit/894f085f402e023a98cbb6f5a3d117bd88d93b09
Conflict:NA

---
 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 c32637af8..f6a21bb77 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);