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

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Message-ID: <20200626082208.GA4559@kunai>
Date:   Fri, 26 Jun 2020 10:22:08 +0200
From:   Wolfram Sang <wsa@...-dreams.de>
To:     Mans Rullgard <mans@...sr.com>
Cc:     linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] i2c: core: check returned size of emulated smbus block
 read

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?

> 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!


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