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authorPetr Písař <ppisar@redhat.com>2018-02-26 13:48:00 +0100
committerSlávek Banko <slavek.banko@axis.cz>2019-03-03 16:04:38 +0100
commit20e7000d0cd56ab6e10d8f22b9caf922e655402c (patch)
tree6c4e3bf1c50c29d6e56c8b78a6b4bfbbb65dbf77 /krfb
parent6221931c63e88eda17f9bd3128470bffb3b2cee3 (diff)
downloadtdenetwork-20e7000d0cd56ab6e10d8f22b9caf922e655402c.tar.gz
tdenetwork-20e7000d0cd56ab6e10d8f22b9caf922e655402c.zip
Limit client cut text length to 1 MB
This patch constrains a client cut text length to 1 MB. Otherwise a client could make server allocate 2 GB of memory and that seems to be to much to classify it as a denial of service. The limit also prevents from an integer overflow followed by copying an uninitilized memory when processing msg.cct.length value larger than SIZE_MAX or INT_MAX - sz_rfbClientCutTextMsg. This patch also corrects accepting length value of zero (malloc(0) is interpreted on differnet systems differently). CVE-2018-7225 <https://github.com/LibVNC/libvncserver/issues/218> (cherry picked from commit 28afb6c537dc82ba04d5f245b15ca7205c6dbb9c)
Diffstat (limited to 'krfb')
-rw-r--r--krfb/libvncserver/rfbserver.c21
1 files changed, 20 insertions, 1 deletions
diff --git a/krfb/libvncserver/rfbserver.c b/krfb/libvncserver/rfbserver.c
index 66cc4ee3..5725d068 100644
--- a/krfb/libvncserver/rfbserver.c
+++ b/krfb/libvncserver/rfbserver.c
@@ -52,6 +52,9 @@ typedef int socklen_t;
#define DEBUGPROTO(x)
#endif
+/* PRIu32 */
+#include <inttypes.h>
+
rfbClientPtr pointerClient = NULL; /* Mutex for pointer events */
static void rfbProcessClientProtocolVersion(rfbClientPtr cl);
@@ -898,7 +901,23 @@ rfbProcessClientNormalMessage(cl)
msg.cct.length = Swap32IfLE(msg.cct.length);
- str = (char *)malloc(msg.cct.length);
+ /* uint32_t input is passed to malloc()'s size_t argument,
+ * to rfbReadExact()'s int argument, to rfbStatRecordMessageRcvd()'s int
+ * argument increased of sz_rfbClientCutTextMsg, and to setXCutText()'s int
+ * argument. Here we impose a limit of 1 MB so that the value fits
+ * into all of the types to prevent from misinterpretation and thus
+ * from accessing uninitialized memory (CVE-2018-7225) and also to
+ * prevent from a denial-of-service by allocating to much memory in
+ * the server. */
+ if (msg.cct.length > 1<<20) {
+ rfbLog("rfbClientCutText: too big cut text length requested: %" PRIu32 "\n",
+ msg.cct.length);
+ rfbCloseClient(cl);
+ return;
+ }
+
+ /* Allow zero-length client cut text. */
+ str = (char *)calloc(msg.cct.length ? msg.cct.length : 1, 1);
if ((n = ReadExact(cl, str, msg.cct.length)) <= 0) {
if (n != 0)