Re: [PATCH] firmware: dmi_scan: Trim DMI table length before exporting it

[Ivan.khoronzhuk]

Hi, Jean

On 26.04.15 23:47, Jean Delvare wrote:
> The SMBIOS v3 entry points specify a maximum length for the DMI table,
> not the exact length. Thus there may be garbage after the end-of-table
> marker, which we don't want to export to user-space. Adjust dmi_len
> when we find the end-of-table marker, so that only the actual table
> payload is exported.

According to above it seems that change doesn't affect SMBIOS < 3.

> Signed-off-by: Jean Delvare <jdelvare@xxxxxxx>
> Cc: Ivan Khoronzhuk <ivan.khoronzhuk@xxxxxxxxxxxxxxx>
> ---
>   drivers/firmware/dmi_scan.c |   15 ++++++++++-----
>   1 file changed, 10 insertions(+), 5 deletions(-)
>
> --- linux-4.1-rc0.orig/drivers/firmware/dmi_scan.c	2015-04-26 18:56:15.657111185 +0200
> +++ linux-4.1-rc0/drivers/firmware/dmi_scan.c	2015-04-26 22:42:59.183547584 +0200
> @@ -108,15 +108,19 @@ static void dmi_decode_table(u8 *buf,
>   		if (data - buf < dmi_len - 1)
>   			decode(dm, private_data);
>   
> +		data += 2;
> +		i++;
> +
>   		/*
>   		 * 7.45 End-of-Table (Type 127) [SMBIOS reference spec v3.0.0]
>   		 */
>   		if (dm->type == DMI_ENTRY_END_OF_TABLE)
>   			break;
> -
> -		data += 2;
> -		i++;
>   	}
> +
> +	/* Trim DMI table length if needed */
> +	if (dmi_len > data - buf)
> +		dmi_len = data - buf;

Why is it checked here? Wouldn't be better to simply assign: dmi_len = 
data - buf;
I guess it's supposed to not trim table in case of exit by i<dmi_num or 
even !dmi_num.
But in this case, probably, it be better to do it in the cycle:

if (dmi->type == DMI_ENTRY_END_OF_TABLE) {
    dmi_len = data - buf;
    break;
}

just to avoid redundant check.

But question is, what if we exit by i<dmi_num?
Wouldn't be better to trim buffer in such case also?

>   }
>   
>   static phys_addr_t dmi_base;
> @@ -125,8 +129,9 @@ static int __init dmi_walk_early(void (*
>   		void *))
>   {
>   	u8 *buf;
> +	u32 orig_dmi_len = dmi_len;
>   
> -	buf = dmi_early_remap(dmi_base, dmi_len);
> +	buf = dmi_early_remap(dmi_base, orig_dmi_len);
>   	if (buf == NULL)
>   		return -1;
>   
> @@ -134,7 +139,7 @@ static int __init dmi_walk_early(void (*
>   
>   	add_device_randomness(buf, dmi_len);
>   
> -	dmi_early_unmap(buf, dmi_len);
> +	dmi_early_unmap(buf, orig_dmi_len);
>   	return 0;
>   }
>   

--
Regards,
Ivan Khoronzhuk

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