+ lib-zlib-dfltcc-deflate-does-not-write-all-available-bits-for-z_no_flush.patch added to mm-nonmm-unstable branch

+ lib-zlib-dfltcc-deflate-does-not-write-all-available-bits-for-z_no_flush.patch added to mm-nonmm-unstable branch

[Andrew Morton]

The patch titled
     Subject: lib/zlib: DFLTCC deflate does not write all available bits for Z_NO_FLUSH
has been added to the -mm mm-nonmm-unstable branch.  Its filename is
     lib-zlib-dfltcc-deflate-does-not-write-all-available-bits-for-z_no_flush.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/lib-zlib-dfltcc-deflate-does-not-write-all-available-bits-for-z_no_flush.patch

This patch will later appear in the mm-nonmm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days

------------------------------------------------------
From: Mikhail Zaslonko <zaslonko@linux.ibm.com>
Subject: lib/zlib: DFLTCC deflate does not write all available bits for Z_NO_FLUSH
Date: Tue, 21 Feb 2023 14:16:17 +0100

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/20230221131617.3369978-2-zaslonko@linux.ibm.com
Signed-off-by: Mikhail Zaslonko <zaslonko@linux.ibm.com>
Acked-by: Ilya Leoshkevich <iii@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 lib/zlib_deflate/defutil.h |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/lib/zlib_deflate/defutil.h~lib-zlib-dfltcc-deflate-does-not-write-all-available-bits-for-z_no_flush
+++ a/lib/zlib_deflate/defutil.h
@@ -420,9 +420,11 @@ static inline void flush_pending(
 	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;
 
_

Patches currently in -mm which might be from zaslonko@linux.ibm.com are

lib-zlib-dfltcc-deflate-does-not-write-all-available-bits-for-z_no_flush.patch