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

On 20/07/2026 12:16, Simon Horman wrote:

On Sat, Jul 11, 2026 at 02:36:41PM +0200, Doruk Tan Ozturk wrote:

quoted

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 <redacted>
---
  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

quoted

+			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