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Re: [Qemu-devel] [PATCH] smbus_eeprom: Limit data writes to 255 bytes

From: Michael Hanselmann
Subject: Re: [Qemu-devel] [PATCH] smbus_eeprom: Limit data writes to 255 bytes
Date: Fri, 28 Dec 2018 17:38:37 +0100

Hi Philippe

On 27.12.18 20:03, Philippe Mathieu-Daudé wrote:
> On Thu, Dec 27, 2018 at 12:53 PM Michael Hanselmann <address@hidden> wrote:
> &gt; The "eeprom_write_data" function in "smbus_eeprom.c" had no provisions
> &gt; to limit the length of data written. If a caller were able to manipulate
> &gt; the "len" parameter they could potentially write before or after the
> &gt; target buffer.
> You forgot to sign your commit:
> "Signed-off-by: Michael Hanselmann <address@hidden>"

Indeed I did and I'm sorry.

Signed-off-by: Michael Hanselmann <address@hidden>

>> diff --git a/hw/i2c/smbus_eeprom.c b/hw/i2c/smbus_eeprom.c
>> index f18aa3de35..74fa1c328c 100644
>> --- a/hw/i2c/smbus_eeprom.c
>> +++ b/hw/i2c/smbus_eeprom.c
>> @@ -76,6 +76,7 @@ static void eeprom_write_data(SMBusDevice *dev, uint8_t 
>> cmd, uint8_t *buf, int l
>>         It is a block write without a length byte.  Fortunately we
>>         get the full block anyway.  */
>>      /* TODO: Should this set the current location?  */
>> +    len &= 0xff;
>>      if (cmd + len > 256)
> Corey Minyard sent a cleanup series [1] because this device model is
> known to be unsafe and need rewrite.
> There is a particular patch [2] which add the SMBUS_EEPROM_SIZE definition.
> He also provided a intent at cleaning this problem here [3] where
> Peter suggested to split it in fewer patches.

I agree with the assessment that the code as-is has room for
improvement, especially when it comes to the hardcoded sizes. My patch
is purely on top of the master branch (ca. QEMU 3.1.0).

Best regards,

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