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Subject: Re: [PATCH] lib: Verify array index is correct before using it
To:     Huang Guobin <huangguobin4@huawei.com>, haren@us.ibm.com,
        ddstreet@ieee.org, herbert@gondor.apana.org.au
Cc:     linux-kernel@vger.kernel.org
References: <20200723134807.35027-1-huangguobin4@huawei.com>
From:   Randy Dunlap <rdunlap@infradead.org>
Message-ID: <08cc095f-bf31-c4e3-0658-f4dfec1d4958@infradead.org>
Date:   Thu, 23 Jul 2020 07:22:53 -0700
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On 7/23/20 6:48 AM, Huang Guobin wrote:
> This code reads from the array before verifying that "c" is a valid
> index. Move test array offset code before use to fix it.
> 
> Fixes: 2da572c959dd ("lib: add software 842 compression/decompression")
> Signed-off-by: Huang Guobin <huangguobin4@huawei.com>

Hi,
Why shouldn't these locations use array_index_nospec() from
#include <linux/nospec.h>
?


> ---
>  lib/842/842_compress.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/lib/842/842_compress.c b/lib/842/842_compress.c
> index c02baa4168e1..10f9f8a0d05b 100644
> --- a/lib/842/842_compress.c
> +++ b/lib/842/842_compress.c
> @@ -222,12 +222,13 @@ static int add_bits(struct sw842_param *p, u64 d, u8 n)
>  static int add_template(struct sw842_param *p, u8 c)
>  {
>  	int ret, i, b = 0;
> -	u8 *t = comp_ops[c];
> +	u8 *t = NULL;
>  	bool inv = false;
>  
>  	if (c >= OPS_MAX)
>  		return -EINVAL;
>  
> +	t = comp_ops[c];
>  	pr_debug("template %x\n", t[4]);
>  
>  	ret = add_bits(p, t[4], OP_BITS);
> @@ -379,12 +380,14 @@ static int add_end_template(struct sw842_param *p)
>  
>  static bool check_template(struct sw842_param *p, u8 c)
>  {
> -	u8 *t = comp_ops[c];
> +	u8 *t = NULL;
>  	int i, match, b = 0;
>  
>  	if (c >= OPS_MAX)
>  		return false;
>  
> +	t = comp_ops[c];
> +
>  	for (i = 0; i < 4; i++) {
>  		if (t[i] & OP_ACTION_INDEX) {
>  			if (t[i] & OP_AMOUNT_2)
> 

thanks.
-- 
~Randy