linux-kernel - Re: [PATCH 1/2] lib: decompress

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <8E3C6FC0-2DF0-49B5-9885-BA4AC81A117D@fb.com>
Date:   Mon, 24 Aug 2020 20:11:12 +0000
From:   Nick Terrell <terrelln@...com>
To:     Paul Cercueil <paul@...pouillou.net>
CC:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        "linux-mips@...r.kernel.org" <linux-mips@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "od@...c.me" <od@...c.me>
Subject: Re: [PATCH 1/2] lib: decompress_unzstd: Limit output size



> On Aug 21, 2020, at 9:29 AM, Paul Cercueil <paul@...pouillou.net> wrote:
> 
> The zstd decompression code, as it is right now, will have internal
> values overflow on 32-bit systems when the output size is LONG_MAX.
> 
> Until someone smarter than me can figure out how to fix the zstd code
> properly, limit the destination buffer size to 512 MiB, which should be
> enough for everybody, in order to make it usable on 32-bit systems.

Can you bump the size up to 2GB? I suspect the problem inside of zstd
is an off-by-one error or something similar, so getting closer to the limit
shouldn't be a problem. I’d feel more comfortable with 2GB, since
kernels can get pretty large.

Hmm, zstd shouldn’t be overflowing that value. I’m currently preparing
a patch to updating the version of zstd in the kernel, and using upstream
directly. I will add a test upstream in 32-bit mode to ensure that we don’t
overflow a 32-bit size_t, so this will be fixed after the update.

-Nick

> Signed-off-by: Paul Cercueil <paul@...pouillou.net>
> ---
> lib/decompress_unzstd.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/decompress_unzstd.c b/lib/decompress_unzstd.c
> index 0ad2c15479ed..e1c03b1eaa6e 100644
> --- a/lib/decompress_unzstd.c
> +++ b/lib/decompress_unzstd.c
> @@ -77,6 +77,7 @@
> 
> #include <linux/decompress/mm.h>
> #include <linux/kernel.h>
> +#include <linux/sizes.h>
> #include <linux/zstd.h>
> 
> /* 128MB is the maximum window size supported by zstd. */
> @@ -179,7 +180,7 @@ static int INIT __unzstd(unsigned char *in_buf, long in_len,
> 	size_t ret;
> 
> 	if (out_len == 0)
> -		out_len = LONG_MAX; /* no limit */
> +		out_len = SZ_512M; /* should be big enough, right? */
> 
> 	if (fill == NULL && flush == NULL)
> 		/*
> -- 
> 2.28.0
>