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authorDaniel P. Berrange <berrange@redhat.com>2015-03-23 22:58:22 +0000
committerGerd Hoffmann <kraxel@redhat.com>2015-04-01 17:12:55 +0200
commit2cdb5e142fb93e875fa53c52864ef5eb8d5d8b41 (patch)
tree6c56b659ac57e398ef32f2a5f77dc9ba95a7d65f
parenta2bebfd6e09d285aa793cae3fb0fc3a39a9fee6e (diff)
downloadqemu-arm-2cdb5e142fb93e875fa53c52864ef5eb8d5d8b41.tar.gz
CVE-2015-1779: limit size of HTTP headers from websockets clients
The VNC server websockets decoder will read and buffer data from websockets clients until it sees the end of the HTTP headers, as indicated by \r\n\r\n. In theory this allows a malicious to trick QEMU into consuming an arbitrary amount of RAM. In practice, because QEMU runs g_strstr_len() across the buffered header data, it will spend increasingly long burning CPU time searching for the substring match and less & less time reading data. So while this does cause arbitrary memory growth, the bigger problem is that QEMU will be burning 100% of available CPU time. A novnc websockets client typically sends headers of around 512 bytes in length. As such it is reasonable to place a 4096 byte limit on the amount of data buffered while searching for the end of HTTP headers. Signed-off-by: Daniel P. Berrange <berrange@redhat.com> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
-rw-r--r--ui/vnc-ws.c10
1 files changed, 8 insertions, 2 deletions
diff --git a/ui/vnc-ws.c b/ui/vnc-ws.c
index 0b7de4e662..62eb97fe76 100644
--- a/ui/vnc-ws.c
+++ b/ui/vnc-ws.c
@@ -81,8 +81,11 @@ void vncws_handshake_read(void *opaque)
VncState *vs = opaque;
uint8_t *handshake_end;
long ret;
- buffer_reserve(&vs->ws_input, 4096);
- ret = vnc_client_read_buf(vs, buffer_end(&vs->ws_input), 4096);
+ /* Typical HTTP headers from novnc are 512 bytes, so limiting
+ * total header size to 4096 is easily enough. */
+ size_t want = 4096 - vs->ws_input.offset;
+ buffer_reserve(&vs->ws_input, want);
+ ret = vnc_client_read_buf(vs, buffer_end(&vs->ws_input), want);
if (!ret) {
if (vs->csock == -1) {
@@ -99,6 +102,9 @@ void vncws_handshake_read(void *opaque)
vncws_process_handshake(vs, vs->ws_input.buffer, vs->ws_input.offset);
buffer_advance(&vs->ws_input, handshake_end - vs->ws_input.buffer +
strlen(WS_HANDSHAKE_END));
+ } else if (vs->ws_input.offset >= 4096) {
+ VNC_DEBUG("End of headers not found in first 4096 bytes\n");
+ vnc_client_error(vs);
}
}