linux-kernel - Re: [PATCH] eeprom: ee1004: limit i2c reads to I2C_SMBUS_BLOCK

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Date:   Thu, 3 Feb 2022 18:10:57 +0100
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Jonas Malaco <jonas@...tocubo.io>, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     stable@...r.kernel.org, Wolfram Sang <wsa@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] eeprom: ee1004: limit i2c reads to I2C_SMBUS_BLOCK_MAX

On 03.02.2022 17:49, Jonas Malaco wrote:
> Commit effa453168a7 ("i2c: i801: Don't silently correct invalid transfer
> size") revealed that ee1004_eeprom_read() did not properly limit how
> many bytes to read at once.
> 
> In particular, i2c_smbus_read_i2c_block_data_or_emulated() takes the
> length to read as an u8.  If count == 256 after taking into account the
> offset and page boundary, the cast to u8 overflows.  And this is common
> when user space tries to read the entire EEPROM at once.
> 
> To fix it, limit each read to I2C_SMBUS_BLOCK_MAX (32) bytes, already
> the maximum length i2c_smbus_read_i2c_block_data_or_emulated() allows.
> 
> Fixes: effa453168a7 ("i2c: i801: Don't silently correct invalid transfer size")
> Cc: stable@...r.kernel.org
> Signed-off-by: Jonas Malaco <jonas@...tocubo.io>
> ---
>  drivers/misc/eeprom/ee1004.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/misc/eeprom/ee1004.c b/drivers/misc/eeprom/ee1004.c
> index bb9c4512c968..9fbfe784d710 100644
> --- a/drivers/misc/eeprom/ee1004.c
> +++ b/drivers/misc/eeprom/ee1004.c
> @@ -114,6 +114,9 @@ static ssize_t ee1004_eeprom_read(struct i2c_client *client, char *buf,
>  	if (offset + count > EE1004_PAGE_SIZE)
>  		count = EE1004_PAGE_SIZE - offset;
>  
> +	if (count > I2C_SMBUS_BLOCK_MAX)
> +		count = I2C_SMBUS_BLOCK_MAX;
> +
>  	return i2c_smbus_read_i2c_block_data_or_emulated(client, offset, count, buf);
>  }
>  
> 
> base-commit: 88808fbbead481aedb46640a5ace69c58287f56a

Reviewed-by: Heiner Kallweit <hkallweit1@...il.com>