lib/zlib: DFLTCC deflate does not write all available bits for Z_NO_FLUSH

DFLTCC deflate with Z_NO_FLUSH might generate a corrupted stream when the
output buffer is not large enough to fit all the deflate output at once.
The problem takes place on closing the deflate block since flush_pending()
might leave some output bits not written. Similar problem for software
deflate with Z_BLOCK flush option (not supported by kernel zlib deflate)
has been fixed a while ago in userspace zlib but the fix never got to the
kernel.

Now flush_pending() flushes the bit buffer before copying out the byte
buffer, in order to really flush as much as possible.

Currently there are no users of DFLTCC deflate with Z_NO_FLUSH option in
the kernel so the problem remained hidden for a while.

This commit is based on the old zlib commit:
https://github.com/madler/zlib/commit/0b828b4

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Mikhail Zaslonko <[e-mail]>
Acked-by: Ilya Leoshkevich <[e-mail]>
Cc: Heiko Carstens <[e-mail]>
Cc: Vasily Gorbik <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

lib/zlib_deflate/defutil.h

···
 	z_streamp strm
 )
 {
+    unsigned len;
     deflate_state *s = (deflate_state *) strm->state;
-    unsigned len = s->pending;
 
+    bi_flush(s);
+    len = s->pending;
     if (len > strm->avail_out) len = strm->avail_out;
     if (len == 0) return;