Re: [PATCH] i2c: smbus: fix NULL function pointer dereference

[Baruch Siach]

Hi Wolfram,

On Fri, Apr 26 2024, Wolfram Sang wrote:
> Brauch reported an OOPS when using the designware controller as target
> only. Target-only modes break the assumption of one transfer function
> always being available. Fix this by always checking the pointer in
> __i2c_transfer.
>
> Reported-by: Baruch Siach <baruch@xxxxxxxxxx>
> Closes: https://lore.kernel.org/r/4269631780e5ba789cf1ae391eec1b959def7d99.1712761976.git.baruch@xxxxxxxxxx
> Fixes: 4b1acc43331d ("i2c: core changes for slave support")
> Signed-off-by: Wolfram Sang <wsa+renesas@xxxxxxxxxxxxxxxxxxxx>

Tested-by: Baruch Siach <baruch@xxxxxxxxxx>

Thanks,
baruch

> ---
>  drivers/i2c/i2c-core-base.c  | 12 ++++++------
>  drivers/i2c/i2c-core-smbus.c |  2 +-
>  2 files changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
> index ff5c486a1dbb..db0d1ac82910 100644
> --- a/drivers/i2c/i2c-core-base.c
> +++ b/drivers/i2c/i2c-core-base.c
> @@ -2200,13 +2200,18 @@ static int i2c_check_for_quirks(struct i2c_adapter *adap, struct i2c_msg *msgs,
>   * Returns negative errno, else the number of messages executed.
>   *
>   * Adapter lock must be held when calling this function. No debug logging
> - * takes place. adap->algo->master_xfer existence isn't checked.
> + * takes place.
>   */
>  int __i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
>  {
>  	unsigned long orig_jiffies;
>  	int ret, try;
>  
> +	if (!adap->algo->master_xfer) {
> +		dev_dbg(&adap->dev, "I2C level transfers not supported\n");
> +		return -EOPNOTSUPP;
> +	}
> +
>  	if (WARN_ON(!msgs || num < 1))
>  		return -EINVAL;
>  
> @@ -2273,11 +2278,6 @@ int i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
>  {
>  	int ret;
>  
> -	if (!adap->algo->master_xfer) {
> -		dev_dbg(&adap->dev, "I2C level transfers not supported\n");
> -		return -EOPNOTSUPP;
> -	}
> -
>  	/* REVISIT the fault reporting model here is weak:
>  	 *
>  	 *  - When we get an error after receiving N bytes from a slave,
> diff --git a/drivers/i2c/i2c-core-smbus.c b/drivers/i2c/i2c-core-smbus.c
> index e3b96fc53b5c..a942c5306a4e 100644
> --- a/drivers/i2c/i2c-core-smbus.c
> +++ b/drivers/i2c/i2c-core-smbus.c
> @@ -596,7 +596,7 @@ s32 __i2c_smbus_xfer(struct i2c_adapter *adapter, u16 addr,
>  				break;
>  		}
>  
> -		if (res != -EOPNOTSUPP || !adapter->algo->master_xfer)
> +		if (res != -EOPNOTSUPP)
>  			goto trace;
>  		/*
>  		 * Fall back to i2c_smbus_xfer_emulated if the adapter doesn't


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