vnc: fix memory leak when vnc disconnect

Currently when qemu receives a vnc connect, it creates a 'VncState' to
represent this connection. In 'vnc_worker_thread_loop' it creates a
local 'VncState'. The connection 'VcnState' and local 'VncState' exchange
data in 'vnc_async_encoding_start' and 'vnc_async_encoding_end'.
In 'zrle_compress_data' it calls 'deflateInit2' to allocate the libz library
opaque data. The 'VncState' used in 'zrle_compress_data' is the local
'VncState'. In 'vnc_zrle_clear' it calls 'deflateEnd' to free the libz
library opaque data. The 'VncState' used in 'vnc_zrle_clear' is the connection
'VncState'. In currently implementation there will be a memory leak when the
vnc disconnect. Following is the asan output backtrack:

Direct leak of 29760 byte(s) in 5 object(s) allocated from:
    0 0xffffa67ef3c3 in __interceptor_calloc (/lib64/libasan.so.4+0xd33c3)
    1 0xffffa65071cb in g_malloc0 (/lib64/libglib-2.0.so.0+0x571cb)
    2 0xffffa5e968f7 in deflateInit2_ (/lib64/libz.so.1+0x78f7)
    3 0xaaaacec58613 in zrle_compress_data ui/vnc-enc-zrle.c:87
    4 0xaaaacec58613 in zrle_send_framebuffer_update ui/vnc-enc-zrle.c:344
    5 0xaaaacec34e77 in vnc_send_framebuffer_update ui/vnc.c:919
    6 0xaaaacec5e023 in vnc_worker_thread_loop ui/vnc-jobs.c:271
    7 0xaaaacec5e5e7 in vnc_worker_thread ui/vnc-jobs.c:340
    8 0xaaaacee4d3c3 in qemu_thread_start util/qemu-thread-posix.c:502
    9 0xffffa544e8bb in start_thread (/lib64/libpthread.so.0+0x78bb)
    10 0xffffa53965cb in thread_start (/lib64/libc.so.6+0xd55cb)

This is because the opaque allocated in 'deflateInit2' is not freed in
'deflateEnd'. The reason is that the 'deflateEnd' calls 'deflateStateCheck'
and in the latter will check whether 's->strm != strm'(libz's data structure).
This check will be true so in 'deflateEnd' it just return 'Z_STREAM_ERROR' and
not free the data allocated in 'deflateInit2'.

The reason this happens is that the 'VncState' contains the whole 'VncZrle',
so when calling 'deflateInit2', the 's->strm' will be the local address.
So 's->strm != strm' will be true.

To fix this issue, we need to make 'zrle' of 'VncState' to be a pointer.
Then the connection 'VncState' and local 'VncState' exchange mechanism will
work as expection. The 'tight' of 'VncState' has the same issue, let's also turn
it to a pointer.

Reported-by: Ying Fang <fangying1@huawei.com>
Signed-off-by: Li Qiang <liq3ea@163.com>
Message-id: 20190831153922.121308-1-liq3ea@163.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

1 files changed, 6 insertions, 5 deletions

diff --git a/ui/vnc-enc-zlib.c b/ui/vnc-enc-zlib.c
index 33e9df2..900ae5b 100644
--- a/ui/vnc-enc-zlib.c
+++ b/ui/vnc-enc-zlib.c
@@ -76,7 +76,8 @@ static int vnc_zlib_stop(VncState *vs)
         zstream->zalloc = vnc_zlib_zalloc;
         zstream->zfree = vnc_zlib_zfree;
 
-        err = deflateInit2(zstream, vs->tight.compression, Z_DEFLATED, MAX_WBITS,
+        err = deflateInit2(zstream, vs->tight->compression, Z_DEFLATED,
+                           MAX_WBITS,
                            MAX_MEM_LEVEL, Z_DEFAULT_STRATEGY);
 
         if (err != Z_OK) {
@@ -84,16 +85,16 @@ static int vnc_zlib_stop(VncState *vs)
             return -1;
         }
 
-        vs->zlib.level = vs->tight.compression;
+        vs->zlib.level = vs->tight->compression;
         zstream->opaque = vs;
     }
 
-    if (vs->tight.compression != vs->zlib.level) {
-        if (deflateParams(zstream, vs->tight.compression,
+    if (vs->tight->compression != vs->zlib.level) {
+        if (deflateParams(zstream, vs->tight->compression,
                           Z_DEFAULT_STRATEGY) != Z_OK) {
             return -1;
         }
-        vs->zlib.level = vs->tight.compression;
+        vs->zlib.level = vs->tight->compression;
     }
 
     // reserve memory in output buffer