linux-kernel - Re: [PATCH v3 1/2] lib: decompress

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Message-ID: <747B4847-08E5-40C9-927B-E1BAC057CF46@fb.com>
Date:   Tue, 1 Sep 2020 22:42:08 +0000
From:   Nick Terrell <terrelln@...com>
To:     Paul Cercueil <paul@...pouillou.net>
CC:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        "od@...c.me" <od@...c.me>,
        "linux-mips@...r.kernel.org" <linux-mips@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/2] lib: decompress_unzstd: Limit output size


> On Sep 1, 2020, at 7:26 AM, Paul Cercueil <paul@...pouillou.net> wrote:
> 
> The zstd decompression code, as it is right now, will most likely fail
> on 32-bit systems, as the default output buffer size causes the buffer's
> end address to overflow.
> 
> Address this issue by setting a sane default to the default output size,
> with a value that won't overflow the buffer's end address.
> 
> Signed-off-by: Paul Cercueil <paul@...pouillou.net>
> ---
> 
> Notes:
>    v2: Change limit to 1 GiB
> 
>    v3: Compute size limit instead of using hardcoded value
> 
> lib/decompress_unzstd.c | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/decompress_unzstd.c b/lib/decompress_unzstd.c
> index 0ad2c15479ed..790abc472f5b 100644
> --- a/lib/decompress_unzstd.c
> +++ b/lib/decompress_unzstd.c
> @@ -178,8 +178,13 @@ static int INIT __unzstd(unsigned char *in_buf, long in_len,
> 	int err;
> 	size_t ret;
> 
> +	/*
> +	 * ZSTD decompression code won't be happy if the buffer size is so big
> +	 * that its end address overflows. When the size is not provided, make
> +	 * it as big as possible without having the end address overflow.
> +	 */
> 	if (out_len == 0)
> -		out_len = LONG_MAX; /* no limit */
> +		out_len = UINTPTR_MAX - (uintptr_t)out_buf;

Great, that works for me. Thanks for fixing this!

Reviewed-by: Nick Terrell <terrelln@...com>

> 	if (fill == NULL && flush == NULL)
> 		/*
> -- 
> 2.28.0
>