nfc: fdp: bound the device-reported read length and fix an skb leak

fdp_nci_i2c_read() takes the next packet length from two device-supplied
bytes and never validates it. The value is a u16 used as the
i2c_master_recv() count into a 261-byte on-stack buffer: a malicious,
counterfeit or malfunctioning controller (or an i2c bus interposer) can
drive it far past the buffer for a stack out-of-bounds write that
clobbers the canary and return address, or below the minimum frame size
(directly, or by truncating the computed sum) so the header/LRC strip
and the next length read run past a short receive. Reject a length
outside [FDP_NCI_I2C_MIN_PAYLOAD, FDP_NCI_I2C_MAX_PAYLOAD], as a
corrupted packet already is, and force resynchronization.

The same loop allocates one data skb per iteration and assumes a length
packet followed by a data packet; a device that sends two data packets
in one call leaks the first skb when the second allocation overwrites
it. Free a previously allocated skb before allocating the next.

Fixes: a06347c04c13 ("NFC: Add Intel Fields Peak NFC solution driver")
Cc: stable@vger.kernel.org
Suggested-by: Simon Horman <horms@kernel.org>
Signed-off-by: Bryam Vargas <hexlabsecurity@proton.me>
Link: https://patch.msgid.link/20260616-b4-disp-b1f8ab4c-v2-1-2d1fe5955325@proton.me
Signed-off-by: David Heidelberg <david@ixit.cz>

1 files changed, 27 insertions, 0 deletions

diff --git a/drivers/nfc/fdp/i2c.c b/drivers/nfc/fdp/i2c.c
index c1896a1d978c..f292e7f37456 100644
--- a/drivers/nfc/fdp/i2c.c
+++ b/drivers/nfc/fdp/i2c.c
@@ -166,9 +166,36 @@ static int fdp_nci_i2c_read(struct fdp_i2c_phy *phy, struct sk_buff **skb)
 		/* Packet that contains a length */
 		if (tmp[0] == 0 && tmp[1] == 0) {
 			phy->next_read_size = (tmp[2] << 8) + tmp[3] + 3;
+
+			/*
+			 * next_read_size is taken from the device and is used
+			 * as the i2c_master_recv() count for the next packet
+			 * and as the data skb size. A value above the receive
+			 * buffer overflows tmp[]; one below the minimum frame
+			 * size runs the header/LRC strip and the length-field
+			 * read past a short receive. Either way the packet is
+			 * corrupt: drop it and force resynchronization.
+			 */
+			if (phy->next_read_size < FDP_NCI_I2C_MIN_PAYLOAD ||
+			    phy->next_read_size > FDP_NCI_I2C_MAX_PAYLOAD) {
+				dev_dbg(&client->dev, "%s: corrupted packet\n",
+					__func__);
+				phy->next_read_size = FDP_NCI_I2C_MIN_PAYLOAD;
+				goto flush;
+			}
 		} else {
 			phy->next_read_size = FDP_NCI_I2C_MIN_PAYLOAD;
 
+			/*
+			 * Only one data packet is delivered per call; if the
+			 * device sends another, do not overwrite and leak the
+			 * skb allocated for the previous one.
+			 */
+			if (*skb) {
+				kfree_skb(*skb);
+				*skb = NULL;
+			}
+
 			*skb = alloc_skb(len, GFP_KERNEL);
 			if (*skb == NULL) {
 				r = -ENOMEM;