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

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Message-ID: <20181128040820.GC19711@1wt.eu>
Date:   Wed, 28 Nov 2018 05:08:20 +0100
From:   Willy Tarreau <w@....eu>
To:     Yueyi Li <liyueyi@...e.com>
Cc:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "donb@...uritymouse.com" <donb@...uritymouse.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] lzo: fix ip overrun during compress.

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