[PATCH] crypto: deflate - fix decompression window size

[PATCH] crypto: deflate - fix decompression window size

[Giovanni Cabiddu]

deflate_decompress() initializes the inflate stream with windowBits set
to -DEFLATE_DEF_WINBITS (11 bits, 2KB window). Valid raw DEFLATE streams
allow window sizes up to MAX_WBITS (15 bits, 32KB).  Using a smaller
window than the one used during compression causes decompression to fail
for externally generated data. This might occur if data is compressed
with a compressor that is not deflate-generic (i.e. this
implementation).

Use -MAX_WBITS when calling zlib_inflateInit2() to accept all valid raw
DEFLATE streams. The inflate workspace allocated in deflate_alloc_stream()
is already sized using zlib_inflate_workspacesize(), which accounts for
the maximum window size, so no allocation change is needed.

Fixes: 08cabc7d3c86 ("crypto: deflate - Convert to acomp")
Signed-off-by: Giovanni Cabiddu <giovanni.cabiddu@intel.com>
Reviewed-by: Laurent M Coquerel <laurent.m.coquerel@intel.com>
---
 crypto/deflate.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/crypto/deflate.c b/crypto/deflate.c
index 46fc7def8d4c..d347e506e6c3 100644
--- a/crypto/deflate.c
+++ b/crypto/deflate.c
@@ -203,7 +203,7 @@ static int deflate_decompress(struct acomp_req *req)
 	s = crypto_acomp_lock_stream_bh(&deflate_streams);
 	ds = s->ctx;
 
-	err = zlib_inflateInit2(&ds->stream, -DEFLATE_DEF_WINBITS);
+	err = zlib_inflateInit2(&ds->stream, -MAX_WBITS);
 	if (err != Z_OK) {
 		err = -EINVAL;
 		goto out;
-- 
2.53.0

Re: [PATCH] crypto: deflate - fix decompression window size

[Herbert Xu]

On Tue, Mar 24, 2026 at 06:08:58PM +0000, Giovanni Cabiddu wrote:
> deflate_decompress() initializes the inflate stream with windowBits set
> to -DEFLATE_DEF_WINBITS (11 bits, 2KB window). Valid raw DEFLATE streams
> allow window sizes up to MAX_WBITS (15 bits, 32KB).  Using a smaller
> window than the one used during compression causes decompression to fail
> for externally generated data. This might occur if data is compressed
> with a compressor that is not deflate-generic (i.e. this
> implementation).
> 
> Use -MAX_WBITS when calling zlib_inflateInit2() to accept all valid raw
> DEFLATE streams. The inflate workspace allocated in deflate_alloc_stream()
> is already sized using zlib_inflate_workspacesize(), which accounts for
> the maximum window size, so no allocation change is needed.
> 
> Fixes: 08cabc7d3c86 ("crypto: deflate - Convert to acomp")

That commit doesn't touch this at all.  I think you meant

commit 62a465c25e99b9a98259a6b7f5bb759f5296d501
Author: Herbert Xu <herbert@gondor.apana.org.au>
Date:   Wed Aug 30 17:56:25 2023 +0800

    crypto: deflate - Remove zlib-deflate

But this simply restored the status quo prior to

commit a368f43d6e3a001e684e9191a27df384fbff12f5
Author: Giovanni Cabiddu <giovanni.cabiddu@intel.com>
Date:   Fri Apr 21 21:54:30 2017 +0100

    crypto: scomp - add support for deflate rfc1950 (zlib)

So the commit message needs to be rewritten to clearly state
why this is needed for the "deflate" algorithm.

Thanks,
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

Re: [PATCH] crypto: deflate - fix decompression window size

[Giovanni Cabiddu]

On Thu, Mar 26, 2026 at 05:44:03PM +0900, Herbert Xu wrote:
> On Tue, Mar 24, 2026 at 06:08:58PM +0000, Giovanni Cabiddu wrote:
> > deflate_decompress() initializes the inflate stream with windowBits set
> > to -DEFLATE_DEF_WINBITS (11 bits, 2KB window). Valid raw DEFLATE streams
> > allow window sizes up to MAX_WBITS (15 bits, 32KB).  Using a smaller
> > window than the one used during compression causes decompression to fail
> > for externally generated data. This might occur if data is compressed
> > with a compressor that is not deflate-generic (i.e. this
> > implementation).
> > 
> > Use -MAX_WBITS when calling zlib_inflateInit2() to accept all valid raw
> > DEFLATE streams. The inflate workspace allocated in deflate_alloc_stream()
> > is already sized using zlib_inflate_workspacesize(), which accounts for
> > the maximum window size, so no allocation change is needed.
> > 
> > Fixes: 08cabc7d3c86 ("crypto: deflate - Convert to acomp")
> 
> That commit doesn't touch this at all.  I think you meant
> 
> commit 62a465c25e99b9a98259a6b7f5bb759f5296d501
> Author: Herbert Xu <herbert@gondor.apana.org.au>
> Date:   Wed Aug 30 17:56:25 2023 +0800
> 
>     crypto: deflate - Remove zlib-deflate
> 
> But this simply restored the status quo prior to
> 
> commit a368f43d6e3a001e684e9191a27df384fbff12f5
> Author: Giovanni Cabiddu <giovanni.cabiddu@intel.com>
> Date:   Fri Apr 21 21:54:30 2017 +0100
> 
>     crypto: scomp - add support for deflate rfc1950 (zlib)
> 
> So the commit message needs to be rewritten to clearly state
> why this is needed for the "deflate" algorithm.
My bad. Sorry about that.

I think the Fixes tag should report either the commit that introduced
deflate-scomp

    commit f6ded09de8bdaa405ab90b1b6c4166e69a23664d
    Author: Giovanni Cabiddu <giovanni.cabiddu@intel.com>
    Date:   Fri Oct 21 13:19:53 2016 +0100

        crypto: acomp - add support for deflate via scomp

OR the one that introduced deflate...

    commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (tag: v2.6.12-rc2)
    Author: Linus Torvalds <torvalds@ppc970.osdl.org>
    Date:   Sat Apr 16 15:20:36 2005 -0700

        Linux-2.6.12-rc2

What do you think?

The motivation for this change is that data compressed with a history
window larger than 2 KB (for example, by QAT or IAA) might not be
decompressed by deflate-generic, which currently initializes the inflate
stream with a 2 KB window.

I'll rework the commit message to make this explicit and resubmit.

Regards,

-- 
Giovanni