Re: [PATCH net] nfc: fdp: bound the device-supplied read size in fdp_nci_i2c_read()

[David Heidelberg <david@ixit.cz>]

On 20/07/2026 12:16, Simon Horman wrote:
> On Sat, Jul 11, 2026 at 02:36:41PM +0200, Doruk Tan Ozturk wrote:
>> fdp_nci_i2c_read() reads a "length packet" from the FDP I2C controller and
>> computes the size of the next I2C transfer from two device-supplied bytes:
>>
>> 	phy->next_read_size = (tmp[2] << 8) + tmp[3] + 3;
>>
>> next_read_size is a u16 (up to 65535) and is never bounded. On the next
>> loop iteration it is used directly as the length passed to
>>
>> 	i2c_master_recv(client, tmp, len);
>>
>> which reads into the fixed 261-byte stack buffer
>> tmp[FDP_NCI_I2C_MAX_PAYLOAD]. A malicious or malfunctioning controller
>> that reports a large length thus overflows the stack buffer -- the
>> r != len check runs only after the read has already happened.
>>
>> Reject a next-read size larger than the buffer and resynchronize.
>>
>> Found by 0sec (https://0sec.ai) using automated source analysis; the
>> missing bound is evident from source. Compile-tested.
>>
>> Fixes: a06347c04c13 ("NFC: Add Intel Fields Peak NFC solution driver")
>> Cc: stable@vger.kernel.org
>> Assisted-by: 0sec:claude-opus-4-8
>> Signed-off-by: Doruk Tan Ozturk <doruk@0sec.ai>
>> ---
>>   drivers/nfc/fdp/i2c.c | 9 ++++++++-
>>   1 file changed, 8 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/nfc/fdp/i2c.c b/drivers/nfc/fdp/i2c.c
>> index c1896a1d978c..581f85f0dfa8 100644
>> --- a/drivers/nfc/fdp/i2c.c
>> +++ b/drivers/nfc/fdp/i2c.c
>> @@ -128,7 +128,7 @@ static const struct nfc_phy_ops i2c_phy_ops = {
>>   
>>   static int fdp_nci_i2c_read(struct fdp_i2c_phy *phy, struct sk_buff **skb)
>>   {
>> -	int r, len;
>> +	int r = -EREMOTEIO, len;
>>   	u8 tmp[FDP_NCI_I2C_MAX_PAYLOAD], lrc, k;
>>   	u16 i;
>>   	struct i2c_client *client = phy->i2c_dev;
>> @@ -140,6 +140,13 @@ static int fdp_nci_i2c_read(struct fdp_i2c_phy *phy, struct sk_buff **skb)
>>   
>>   		len = phy->next_read_size;
>>   
>> +		if (len > FDP_NCI_I2C_MAX_PAYLOAD) {
>> +			dev_dbg(&client->dev, "%s: read size %d too large\n",
>> +				__func__, len);
>> +			phy->next_read_size = FDP_NCI_I2C_MIN_PAYLOAD;
> 
> I think it would be more robust to explicitly set r here.
> Because it is assigned a little later in the loop, overriding
> the default assignment made by the first hunk of this patch.

I agree, I was looking at this patch yesterday and the current format feels 
unfavorable.

Please send next revision with Simon suggestion :)

Thank you both!
David

> 
>> +			goto flush;
>> +		}
>> +
>>   		r = i2c_master_recv(client, tmp, len);
>>   		if (r != len) {
>>   			dev_dbg(&client->dev, "%s: i2c recv err: %d\n",
>> -- 
>> 2.43.0
>>

-- 
David Heidelberg