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From e7d578afbb16592ccee8f13aedd65b2220e220ae 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: Tue, 6 Mar 2018 11:58:02 +0100
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Subject: [PATCH] Limit client cut text length to 1 MB
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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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This patch constrains client text length to 1 MB. Otherwise a client
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could make server allocate 2 GB of memory and that seems to be to much
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to classify it as denial of service.
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I keep the previous checks for maximal type values intentionally as
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a course of defensive coding. (You cannot never know how small the
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types are. And as a warning for people patching out this change not to
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introduce CVE-2018-7225 again.)
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Signed-off-by: Petr Písař <ppisar@redhat.com>
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---
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libvncserver/rfbserver.c | 4 +++-
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1 file changed, 3 insertions(+), 1 deletion(-)
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diff --git a/libvncserver/rfbserver.c b/libvncserver/rfbserver.c
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index a9561fc..0027343 100644
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--- a/libvncserver/rfbserver.c
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+++ b/libvncserver/rfbserver.c
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@@ -2587,7 +2587,9 @@ rfbProcessClientNormalMessage(rfbClientPtr cl)
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* argument. Here we check that the value fits into all of them to
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* prevent from misinterpretation and thus from accessing uninitialized
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* memory. CVE-2018-7225 */
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- if (msg.cct.length > SIZE_MAX || msg.cct.length > INT_MAX - sz_rfbClientCutTextMsg) {
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+ /* But first to prevent from a denial-of-service by allocating to much
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+ * memory in the server, we impose a limit of 1 MB. */
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+ if (msg.cct.length > 1<<20 || msg.cct.length > SIZE_MAX || msg.cct.length > INT_MAX - sz_rfbClientCutTextMsg) {
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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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--
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2.13.6
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