73 lines
3.0 KiB
Diff
73 lines
3.0 KiB
Diff
From 03c519ff5831ba75120e00ebebbf1d5a1f7220ab Mon Sep 17 00:00:00 2001
|
|
From: Michael Hanselmann <public@hansmi.ch>
|
|
Date: Sun, 8 Aug 2021 15:35:58 +0200
|
|
Subject: [PATCH] Avoid use-after-free in serialization
|
|
|
|
Serializing parsers with large amounts of buffered write data (e.g. in case of
|
|
a slow or blocked write destination) would cause "serialize_data" to reallocate
|
|
the state buffer whose default size is 64kB (USBREDIRPARSER_SERIALIZE_BUF_SIZE).
|
|
The pointer to the position for the write buffer count would then point to
|
|
a location outside the buffer where the number of write buffers would be written
|
|
as a 32-bit value.
|
|
|
|
As of QEMU 5.2.0 the serializer is invoked for migrations. Serializations for
|
|
migrations may happen regularily such as when using the COLO feature[1].
|
|
Serialization happens under QEMU's I/O lock. The guest can't control the state
|
|
while the serialization is happening. The value written is the number of
|
|
outstanding buffers which would be suceptible to timing and host system system
|
|
load. The guest would have to continously groom the write buffers. A useful
|
|
value needs to be allocated in the exact position freed during the buffer size
|
|
increase, but before the buffer count is written. The author doesn't consider it
|
|
realistic to exploit this use-after-free reliably.
|
|
|
|
[1] https://wiki.qemu.org/Features/COLO
|
|
|
|
Signed-off-by: Michael Hanselmann <public@hansmi.ch>
|
|
---
|
|
usbredirparser/usbredirparser.c | 8 +++++---
|
|
1 file changed, 5 insertions(+), 3 deletions(-)
|
|
|
|
diff --git a/usbredirparser/usbredirparser.c b/usbredirparser/usbredirparser.c
|
|
index d1f9850..dc5f5a4 100644
|
|
--- a/usbredirparser/usbredirparser.c
|
|
+++ b/usbredirparser/usbredirparser.c
|
|
@@ -20,6 +20,7 @@
|
|
*/
|
|
#include "config.h"
|
|
|
|
+#include <stddef.h>
|
|
#include <stdio.h>
|
|
#include <stdlib.h>
|
|
#include <stdarg.h>
|
|
@@ -1580,8 +1581,9 @@ int usbredirparser_serialize(struct usbredirparser *parser_pub,
|
|
struct usbredirparser_priv *parser =
|
|
(struct usbredirparser_priv *)parser_pub;
|
|
struct usbredirparser_buf *wbuf;
|
|
- uint8_t *write_buf_count_pos, *state = NULL, *pos = NULL;
|
|
+ uint8_t *state = NULL, *pos = NULL;
|
|
uint32_t write_buf_count = 0, len, remain = 0;
|
|
+ ptrdiff_t write_buf_count_pos;
|
|
|
|
*state_dest = NULL;
|
|
*state_len = 0;
|
|
@@ -1626,7 +1628,7 @@ int usbredirparser_serialize(struct usbredirparser *parser_pub,
|
|
parser->data, parser->data_read, "packet-data"))
|
|
return -1;
|
|
|
|
- write_buf_count_pos = pos;
|
|
+ write_buf_count_pos = pos - state;
|
|
/* To be replaced with write_buf_count later */
|
|
if (serialize_int(parser, &state, &pos, &remain, 0, "write_buf_count"))
|
|
return -1;
|
|
@@ -1641,7 +1643,7 @@ int usbredirparser_serialize(struct usbredirparser *parser_pub,
|
|
wbuf = wbuf->next;
|
|
}
|
|
/* Patch in write_buf_count */
|
|
- memcpy(write_buf_count_pos, &write_buf_count, sizeof(int32_t));
|
|
+ memcpy(state + write_buf_count_pos, &write_buf_count, sizeof(int32_t));
|
|
|
|
/* Patch in length */
|
|
len = pos - state;
|
|
--
|
|
2.23.0
|