[PATCH] nfc: st95hf: validate device-reported response length before reading

["Tianchu Chen" <tianchu.chen@linux.dev>]

From: Tianchu Chen <flynnnchen@tencent.com>

st95hf_spi_recv_response() reads a 2-byte header from the device,
derives the total response length from it (up to 1025 bytes via the
long-frame encoding) and then blindly reads len - 2 more bytes into
the caller's buffer, whose size it knows nothing about.

Call sites can be overflowed by a device reporting a large length, 
for example, st95hf_irq_thread_handler() passes the data area of a
280-byte skb.

ST95HF datasheet states "In Reader mode it is possible to receive up to
528 bytes of frame data from VICC and TypeB cards", so technically a bogus
NFC tag may trigger the OOB-write if the card-reader's firmware allows
large packets.

Add a buff_len parameter and reject a device-reported length that does
not fit into the caller's buffer before issuing the second SPI
transfer. Also modify callers to pass their real buffer sizes.

Discovered by Atuin - Automated Vulnerability Discovery Engine.

Fixes: cab47333f0f75 ("NFC: Add STMicroelectronics ST95HF driver")
Cc: stable@vger.kernel.org
Signed-off-by: Tianchu Chen <flynnnchen@tencent.com>
---
 drivers/nfc/st95hf/core.c | 6 ++++--
 drivers/nfc/st95hf/spi.c  | 7 ++++++-
 drivers/nfc/st95hf/spi.h  | 2 +-
 3 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/drivers/nfc/st95hf/core.c b/drivers/nfc/st95hf/core.c
index 4d772a308bfff..0fbb60deada23 100644
--- a/drivers/nfc/st95hf/core.c
+++ b/drivers/nfc/st95hf/core.c
@@ -283,7 +283,8 @@ static int st95hf_send_recv_cmd(struct st95hf_context *st95context,
 		unsigned char st95hf_response_arr[2];
 
 		ret = st95hf_spi_recv_response(&st95context->spicontext,
-					       st95hf_response_arr);
+					       st95hf_response_arr,
+					       sizeof(st95hf_response_arr));
 		if (ret < 0) {
 			dev_err(dev, "spi error from st95hf_spi_recv_response(), err = 0x%x\n",
 				ret);
@@ -800,7 +801,8 @@ static irqreturn_t st95hf_irq_thread_handler(int irq, void  *st95hfcontext)
 
 	mutex_lock(&stcontext->rm_lock);
 	res_len = st95hf_spi_recv_response(&stcontext->spicontext,
-					   skb_resp->data);
+					   skb_resp->data,
+					   skb_tailroom(skb_resp));
 	if (res_len < 0) {
 		dev_err(spidevice, "TISR spi response err = 0x%x\n", res_len);
 		result = res_len;
diff --git a/drivers/nfc/st95hf/spi.c b/drivers/nfc/st95hf/spi.c
index ffaf2789c4069..f48abd09a08fc 100644
--- a/drivers/nfc/st95hf/spi.c
+++ b/drivers/nfc/st95hf/spi.c
@@ -66,7 +66,7 @@ EXPORT_SYMBOL_GPL(st95hf_spi_send);
 
 /* Function to Receive command Response */
 int st95hf_spi_recv_response(struct st95hf_spi_context *spicontext,
-			     unsigned char *receivebuff)
+			     unsigned char *receivebuff, int buff_len)
 {
 	int len = 0;
 	struct spi_transfer tx_takedata;
@@ -106,6 +106,11 @@ int st95hf_spi_recv_response(struct st95hf_spi_context *spicontext,
 	else
 		len += receivebuff[1];
 
+	if (len > buff_len) {
+		mutex_unlock(&spicontext->spi_lock);
+		return -E2BIG;
+	}
+
 	/* Now make a transfer to read only relevant bytes */
 	tx_takedata.rx_buf = &receivebuff[2];
 	tx_takedata.len = len - 2;
diff --git a/drivers/nfc/st95hf/spi.h b/drivers/nfc/st95hf/spi.h
index 3ab678734c174..443a5053c0128 100644
--- a/drivers/nfc/st95hf/spi.h
+++ b/drivers/nfc/st95hf/spi.h
@@ -45,7 +45,7 @@ int st95hf_spi_send(struct st95hf_spi_context *spicontext,
 		    enum req_type reqtype);
 
 int st95hf_spi_recv_response(struct st95hf_spi_context *spicontext,
-			     unsigned char *receivebuff);
+			     unsigned char *receivebuff, int buff_len);
 
 int st95hf_spi_recv_echo_res(struct st95hf_spi_context *spicontext,
 			     unsigned char *receivebuff);
-- 
2.51.0