From: Nick Terrell <terrelln@fb.com>
To: Paul Cercueil <paul@crapouillou.net>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
"linux-mips@vger.kernel.org" <linux-mips@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"od@zcrc.me" <od@zcrc.me>
Subject: Re: [PATCH 1/2] lib: decompress_unzstd: Limit output size
Date: Mon, 24 Aug 2020 20:11:12 +0000 [thread overview]
Message-ID: <8E3C6FC0-2DF0-49B5-9885-BA4AC81A117D@fb.com> (raw)
In-Reply-To: <20200821162948.146947-1-paul@crapouillou.net>
> On Aug 21, 2020, at 9:29 AM, Paul Cercueil <paul@crapouillou.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@crapouillou.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
>
next prev parent reply other threads:[~2020-08-24 20:11 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-21 16:29 [PATCH 1/2] lib: decompress_unzstd: Limit output size Paul Cercueil
2020-08-21 16:29 ` [PATCH 2/2] MIPS: Add support for ZSTD-compressed kernels Paul Cercueil
2020-08-24 19:51 ` Nick Terrell
2020-08-24 21:02 ` Paul Cercueil
2020-08-24 21:45 ` Nick Terrell
2020-08-24 20:11 ` Nick Terrell [this message]
2020-08-24 21:05 ` [PATCH 1/2] lib: decompress_unzstd: Limit output size Paul Cercueil
2020-08-24 21:50 ` Nick Terrell
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