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SubjectRe: [PATCH] firmware: dmi_scan: Trim DMI table length before exporting it
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@suse.de>
> Cc: Ivan Khoronzhuk <ivan.khoronzhuk@globallogic.com>
> ---
> 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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