File xsa326-12.patch of Package xen.28171

From 3ecf15728d7516e7564f29d2dd76724a3ed96cc4 Mon Sep 17 00:00:00 2001
From: Juergen Gross <jgross@suse.com>
Date: Tue, 13 Sep 2022 07:35:09 +0200
Subject: tools/xenstore: add memory accounting for responses

Add the memory accounting for queued responses.

In case adding a watch event for a guest is causing the hard memory
quota of that guest to be violated, the event is dropped. This will
ensure that it is impossible to drive another guest past its memory
quota by generating insane amounts of events for that guest. This is
especially important for protecting driver domains from that attack
vector.

This is part of XSA-326 / CVE-2022-42315.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Julien Grall <jgrall@amazon.com>

diff --git a/tools/xenstore/xenstored_core.c b/tools/xenstore/xenstored_core.c
index 9fd83ea0259a..4322d3cf63a1 100644
--- a/tools/xenstore/xenstored_core.c
+++ b/tools/xenstore/xenstored_core.c
@@ -257,6 +257,8 @@ static void free_buffered_data(struct buffered_data *out,
 		}
 	}
 
+	domain_memory_add_nochk(conn->id, -out->hdr.msg.len - sizeof(out->hdr));
+
 	if (out->hdr.msg.type == XS_WATCH_EVENT) {
 		req = out->pend.req;
 		if (req) {
@@ -845,11 +847,14 @@ void send_reply(struct connection *conn, enum xsd_sockmsg_type type,
 	bdata->timeout_msec = 0;
 	bdata->watch_event = false;
 
-	if (len <= DEFAULT_BUFFER_SIZE)
+	if (len <= DEFAULT_BUFFER_SIZE) {
 		bdata->buffer = bdata->default_buffer;
-	else {
+		/* Don't check quota, path might be used for returning error. */
+		domain_memory_add_nochk(conn->id, len + sizeof(bdata->hdr));
+	} else {
 		bdata->buffer = talloc_array(bdata, char, len);
-		if (!bdata->buffer) {
+		if (!bdata->buffer ||
+		    domain_memory_add_chk(conn->id, len + sizeof(bdata->hdr))) {
 			send_error(conn, ENOMEM);
 			return;
 		}
@@ -914,6 +919,11 @@ void send_event(struct buffered_data *req, struct connection *conn,
 		}
 	}
 
+	if (domain_memory_add_chk(conn->id, len + sizeof(bdata->hdr))) {
+		talloc_free(bdata);
+		return;
+	}
+
 	if (timeout_watch_event_msec && domain_is_unprivileged(conn)) {
 		bdata->timeout_msec = get_now_msec() + timeout_watch_event_msec;
 		if (!conn->timeout_msec)