Re: [PATCH] lzo: fix ip overrun during compress.

From: Willy Tarreau <w@1wt.eu>
To: Yueyi Li <liyueyi@live.com>
Cc: "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
	"donb@securitymouse.com" <donb@securitymouse.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] lzo: fix ip overrun during compress.
Date: Wed, 28 Nov 2018 05:08:20 +0100	[thread overview]
Message-ID: <20181128040820.GC19711@1wt.eu> (raw)
In-Reply-To: <BLUPR13MB0289FB16D885625827E8DD27DFD00@BLUPR13MB0289.namprd13.prod.outlook.com>

Hi Yueyi,

On Tue, Nov 27, 2018 at 10:34:26AM +0000, Yueyi Li wrote:
> It`s possible ip overrun in lzo1x_1_do_compress() when compressed page is
> point to the end of memory and which virtual address is 0xfffffffffffff000.
> Leading to a NULL pointer access during the get_unaligned_le32(ip).

Thanks for this report.

(...)
> diff --git a/lib/lzo/lzo1x_compress.c b/lib/lzo/lzo1x_compress.c
> index 236eb21..a0265a6 100644
> --- a/lib/lzo/lzo1x_compress.c
> +++ b/lib/lzo/lzo1x_compress.c
> @@ -17,6 +17,9 @@
>  #include <linux/lzo.h>
>  #include "lzodefs.h"
>  
> +#define OVERFLOW_ADD_CHECK(a, b)  \
> +	((size_t)~0 - (size_t)(a) < (size_t)(b) ? true : false)
> +

I think the test would be easier to grasp this way :

#define OVERFLOW_ADD_CHECK(a, b)  \
	((size_t)(b) >= (size_t)((void*)0 - (void *)(a)))

But the following should be more efficient since we build with
-fno-strict-overflow :

#define OVERFLOW_ADD_CHECK(a, b)  \
	(((a) + (b)) < (a))

Could you please recheck ?

Thanks,
Willy