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From 5e5d757a039a60cba5ac89fe1998673c49a2d0b6 Mon Sep 17 00:00:00 2001
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Message-Id: <5e5d757a039a60cba5ac89fe1998673c49a2d0b6@dist-git>
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From: "Daniel P. Berrange" <berrange@redhat.com>
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Date: Tue, 16 Jan 2018 17:00:11 +0000
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Subject: [PATCH] qemu: avoid denial of service reading from QEMU monitor
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(CVE-2018-5748)
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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We read from QEMU until seeing a \r\n pair to indicate a completed reply
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or event. To avoid memory denial-of-service though, we must have a size
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limit on amount of data we buffer. 10 MB is large enough that it ought
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to cope with normal QEMU replies, and small enough that we're not
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consuming unreasonable mem.
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Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
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(cherry picked from commit bc251ea91bcfddd2622fce6bce701a438b2e7276)
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Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
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Reviewed-by: Ján Tomko <jtomko@redhat.com>
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---
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src/qemu/qemu_monitor.c | 15 +++++++++++++++
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1 file changed, 15 insertions(+)
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diff --git a/src/qemu/qemu_monitor.c b/src/qemu/qemu_monitor.c
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index b6af209a83..d999f2d10c 100644
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--- a/src/qemu/qemu_monitor.c
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+++ b/src/qemu/qemu_monitor.c
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@@ -55,6 +55,15 @@ VIR_LOG_INIT("qemu.qemu_monitor");
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#define DEBUG_IO 0
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#define DEBUG_RAW_IO 0
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+/* We read from QEMU until seeing a \r\n pair to indicate a
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+ * completed reply or event. To avoid memory denial-of-service
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+ * though, we must have a size limit on amount of data we
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+ * buffer. 10 MB is large enough that it ought to cope with
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+ * normal QEMU replies, and small enough that we're not
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+ * consuming unreasonable mem.
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+ */
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+#define QEMU_MONITOR_MAX_RESPONSE (10 * 1024 * 1024)
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+
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struct _qemuMonitor {
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virObjectLockable parent;
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@@ -574,6 +583,12 @@ qemuMonitorIORead(qemuMonitorPtr mon)
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int ret = 0;
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if (avail < 1024) {
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+ if (mon->bufferLength >= QEMU_MONITOR_MAX_RESPONSE) {
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+ virReportSystemError(ERANGE,
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+ _("No complete monitor response found in %d bytes"),
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+ QEMU_MONITOR_MAX_RESPONSE);
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+ return -1;
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+ }
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if (VIR_REALLOC_N(mon->buffer,
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mon->bufferLength + 1024) < 0)
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return -1;
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--
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2.17.0
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