From d0b7ef97c4c5fe871664f2a952c8c3b0b4417d23 Mon Sep 17 00:00:00 2001
Message-Id: <d0b7ef97c4c5fe871664f2a952c8c3b0b4417d23@dist-git>
From: =?UTF-8?q?Daniel=20P=2E=20Berrang=C3=A9?= <berrange@redhat.com>
Date: Thu, 1 Mar 2018 14:55:26 +0000
Subject: [PATCH] qemu: avoid denial of service reading from QEMU guest agent
 (CVE-2018-1064)
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We read from the agent until seeing a \r\n pair to indicate a completed
reply or event. To avoid memory denial-of-service though, we must have a
size limit on amount of data we buffer. 10 MB is large enough that it
ought to cope with normal agent replies, and small enough that we're not
consuming unreasonable mem.

This is identical to the flaw we had reading from the QEMU monitor
as CVE-2018-5748, so rather embarrassing that we forgot to fix
the agent code at the same time.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
(cherry picked from commit fbf31e1a4cd19d6f6e33e0937a009775cd7d9513)
Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>
---
 src/qemu/qemu_agent.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/src/qemu/qemu_agent.c b/src/qemu/qemu_agent.c
index 5d125c4138..9cf767bd8a 100644
--- a/src/qemu/qemu_agent.c
+++ b/src/qemu/qemu_agent.c
@@ -53,6 +53,15 @@ VIR_LOG_INIT("qemu.qemu_agent");
 #define DEBUG_IO 0
 #define DEBUG_RAW_IO 0
 
+/* We read from QEMU until seeing a \r\n pair to indicate a
+ * completed reply or event. To avoid memory denial-of-service
+ * though, we must have a size limit on amount of data we
+ * buffer. 10 MB is large enough that it ought to cope with
+ * normal QEMU replies, and small enough that we're not
+ * consuming unreasonable mem.
+ */
+#define QEMU_AGENT_MAX_RESPONSE (10 * 1024 * 1024)
+
 /* When you are the first to uncomment this,
  * don't forget to uncomment the corresponding
  * part in qemuAgentIOProcessEvent as well.
@@ -535,6 +544,12 @@ qemuAgentIORead(qemuAgentPtr mon)
     int ret = 0;
 
     if (avail < 1024) {
+        if (mon->bufferLength >= QEMU_AGENT_MAX_RESPONSE) {
+            virReportSystemError(ERANGE,
+                                 _("No complete agent response found in %d bytes"),
+                                 QEMU_AGENT_MAX_RESPONSE);
+            return -1;
+        }
         if (VIR_REALLOC_N(mon->buffer,
                           mon->bufferLength + 1024) < 0)
             return -1;
-- 
2.17.0