linux-kernel - Re: [PATCH] i2c: core: check returned size of emulated smbus block read

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Date:   Fri, 26 Jun 2020 14:33:54 +0100
From:   Måns Rullgård <mans@...sr.com>
To:     Wolfram Sang <wsa@...-dreams.de>
Cc:     linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] i2c: core: check returned size of emulated smbus block read

Wolfram Sang <wsa@...-dreams.de> writes:

> On Sat, Jun 13, 2020 at 11:41:09AM +0100, Mans Rullgard wrote:
>> If the i2c bus driver ignores the I2C_M_RECV_LEN flag (as some of
>> them do), it is possible for an I2C_SMBUS_BLOCK_DATA read issued
>
> Out of interest, which driver did you use?

I saw it with the mv64xxx (Allwinner) and omap (Beaglebone) drivers.
>From a quick look, it seems like quite a few others have the same
problem.

>> on some random device to return an arbitrary value in the first
>> byte (and nothing else).  When this happens, i2c_smbus_xfer_emulated()
>> will happily write past the end of the supplied data buffer, thus
>> causing Bad Things to happen.  To prevent this, check the size
>> before copying the data block and return an error if it is too large.
>
> Good catch, we were relying on the drivers too much here. I think the
> same fix is needed for the non-emulated case as well. Will have a look.
>
>> +			if (msg[1].buf[0] > I2C_SMBUS_BLOCK_MAX) {
>> +				dev_err(&adapter->dev,
>> +					"Invalid block size returned: %d\n",
>> +					msg[1].buf[0]);
>> +				status = -EINVAL;
>
> I changed this to -EPROTO as described in
> Documentation/i2c/fault-codes.rst.
>
> Applied to for-current, thanks!
>

-- 
Måns Rullgård