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vnc: tight: Fix crash after 2GB of output

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fix 2Gb integer overflow in in VNC tight and zlib encodings

As found by Roland Dreier <roland@purestorage.com> (excellent
catch!), when amount of VNC compressed data produced by zlib
and sent to client exceeds 2Gb, integer overflow occurs because
currently, we calculate amount of data produced at each step by
comparing saved total_out with new total_out, and total_out is
something which grows without bounds.  Compare it with previous
avail_out instead of total_out, and leave total_out alone.

The same code is used in vnc-enc-tight.c and vnc-enc-zlib.c,
so fix both cases.

There, there's no actual need to save previous_out value, since
capacity-offset (which is how that value is calculated) stays
the same so it can be recalculated again after call to deflate(),
but whole thing becomes less readable this way.

Reported-by: Roland Dreier <roland@purestorage.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
Signed-off-by: Corentin Chary <corentin.chary@gmail.com>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
This commit is contained in:
Michael Tokarev 2011-03-21 09:34:35 +01:00 committed by Aurelien Jarno
parent a88df0b9b5
commit 2caa9e9d2e
2 changed files with 5 additions and 4 deletions
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5
ui/vnc-enc-tight.c
View file

@ -868,8 +868,8 @@ static int tight_compress_data(VncState *vs, int stream_id, size_t bytes,
zstream->avail_in = vs->tight.tight.offset;
zstream->next_out = vs->tight.zlib.buffer + vs->tight.zlib.offset;
zstream->avail_out = vs->tight.zlib.capacity - vs->tight.zlib.offset;
previous_out = zstream->avail_out;
zstream->data_type = Z_BINARY;
previous_out = zstream->total_out;
/* start encoding */
if (deflate(zstream, Z_SYNC_FLUSH) != Z_OK) {
@ -878,7 +878,8 @@ static int tight_compress_data(VncState *vs, int stream_id, size_t bytes,
}
vs->tight.zlib.offset = vs->tight.zlib.capacity - zstream->avail_out;
bytes = zstream->total_out - previous_out;
/* ...how much data has actually been produced by deflate() */
bytes = previous_out - zstream->avail_out;
tight_send_compact_size(vs, bytes);
vnc_write(vs, vs->tight.zlib.buffer, bytes);

4
ui/vnc-enc-zlib.c
View file

@ -103,8 +103,8 @@ static int vnc_zlib_stop(VncState *vs)
zstream->avail_in = vs->zlib.zlib.offset;
zstream->next_out = vs->output.buffer + vs->output.offset;
zstream->avail_out = vs->output.capacity - vs->output.offset;
previous_out = zstream->avail_out;
zstream->data_type = Z_BINARY;
previous_out = zstream->total_out;
// start encoding
if (deflate(zstream, Z_SYNC_FLUSH) != Z_OK) {
@ -113,7 +113,7 @@ static int vnc_zlib_stop(VncState *vs)
}
vs->output.offset = vs->output.capacity - zstream->avail_out;
return zstream->total_out - previous_out;
return previous_out - zstream->avail_out;
}
int vnc_zlib_send_framebuffer_update(VncState *vs, int x, int y, int w, int h)