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From 11beef0b7f1ed290348e45618e5fa0d2bffcb72e Mon Sep 17 00:00:00 2001
From: Peter Hutterer <peter.hutterer@who-t.net>
Date: Tue, 5 Jul 2022 12:06:20 +1000
Subject: xkb: proof GetCountedString against request length attacks
GetCountedString did a check for the whole string to be within the
request buffer but not for the initial 2 bytes that contain the length
field. A swapped client could send a malformed request to trigger a
swaps() on those bytes, writing into random memory.
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
---
xkb/xkb.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/xkb/xkb.c b/xkb/xkb.c
index f42f59ef3..1841cff26 100644
--- a/xkb/xkb.c
+++ b/xkb/xkb.c
@@ -5137,6 +5137,11 @@ _GetCountedString(char **wire_inout, ClientPtr client, char **str)
CARD16 len;
wire = *wire_inout;
+
+ if (client->req_len <
+ bytes_to_int32(wire + 2 - (char *) client->requestBuffer))
+ return BadValue;
+
len = *(CARD16 *) wire;
if (client->swapped) {
swaps(&len);
--
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