62 lines
2.2 KiB
Diff
62 lines
2.2 KiB
Diff
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From 28afb6c537dc82ba04d5f245b15ca7205c6dbb9c Mon Sep 17 00:00:00 2001
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From: =?UTF-8?q?Petr=20P=C3=ADsa=C5=99?= <ppisar@redhat.com>
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Date: Mon, 26 Feb 2018 13:48:00 +0100
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Subject: [PATCH] Limit client cut text length to 1 MB
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This patch constrains a client cut text length to 1 MB. Otherwise
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a client could make server allocate 2 GB of memory and that seems to
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be to much to classify it as a denial of service.
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The limit also prevents from an integer overflow followed by copying
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an uninitilized memory when processing msg.cct.length value larger
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than SIZE_MAX or INT_MAX - sz_rfbClientCutTextMsg.
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This patch also corrects accepting length value of zero (malloc(0) is
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interpreted on differnet systems differently).
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CVE-2018-7225
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<https://github.com/LibVNC/libvncserver/issues/218>
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---
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libvncserver/rfbserver.c | 20 +++++++++++++++++++-
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1 file changed, 19 insertions(+), 1 deletion(-)
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diff --git a/libvncserver/rfbserver.c b/libvncserver/rfbserver.c
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index 116c4889..4fc4d9d5 100644
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--- libvncserver/rfbserver.c
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+++ libvncserver/rfbserver.c
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@@ -88,6 +88,8 @@
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#include <errno.h>
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/* strftime() */
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#include <time.h>
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+/* PRIu32 */
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+#include <inttypes.h>
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#ifdef LIBVNCSERVER_WITH_WEBSOCKETS
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#include "rfbssl.h"
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@@ -2575,7 +2577,23 @@ rfbProcessClientNormalMessage(rfbClientPtr cl)
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msg.cct.length = Swap32IfLE(msg.cct.length);
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- str = (char *)malloc(msg.cct.length);
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+ /* uint32_t input is passed to malloc()'s size_t argument,
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+ * to rfbReadExact()'s int argument, to rfbStatRecordMessageRcvd()'s int
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+ * argument increased of sz_rfbClientCutTextMsg, and to setXCutText()'s int
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+ * argument. Here we impose a limit of 1 MB so that the value fits
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+ * into all of the types to prevent from misinterpretation and thus
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+ * from accessing uninitialized memory (CVE-2018-7225) and also to
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+ * prevent from a denial-of-service by allocating to much memory in
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+ * the server. */
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+ if (msg.cct.length > 1<<20) {
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+ rfbLog("rfbClientCutText: too big cut text length requested: %" PRIu32 "\n",
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+ msg.cct.length);
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+ rfbCloseClient(cl);
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+ return;
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+ }
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+
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+ /* Allow zero-length client cut text. */
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+ str = (char *)calloc(msg.cct.length ? msg.cct.length : 1, 1);
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if (str == NULL) {
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rfbLogPerror("rfbProcessClientNormalMessage: not enough memory");
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rfbCloseClient(cl);
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