[PATCH wpan] ieee802154: ca8210: fix pointer truncation in kfifo on 64-bit

ca8210_test_int_driver_write() and ca8210_test_int_user_read() exchange
a kmalloc'd buffer pointer through a struct kfifo, but pass a literal
'4' as the byte count to kfifo_in()/kfifo_out().

This is correct on 32-bit (pointer = 4 bytes), but on 64-bit only the
low 4 bytes of the 8-byte pointer are written into the FIFO. The reader
then reads back 4 bytes into an 8-byte local pointer variable, leaving
the upper 4 bytes uninitialized stack data. The first dereference of
the reconstructed pointer (fifo_buffer[1]) accesses an arbitrary kernel
address and generally results in an oops.

Use sizeof(fifo_buffer) so the byte count matches pointer width on every
architecture.

The driver has no architecture restriction in Kconfig, so any 64-bit
build with CONFIG_IEEE802154_CA8210_DEBUGFS=y is exposed. Issue has
been latent since the driver was added in 2017 because it is most
commonly deployed on 32-bit MCUs.

Found via a custom Coccinelle semantic patch hunting for short-byte
kfifo I/O on byte-mode kfifos used to shuttle pointers.

Fixes: ded845a781a5 ("ieee802154: Add CA8210 IEEE 802.15.4 device driver")
Signed-off-by: Shitalkumar Gandhi <[email protected]>
---
 drivers/net/ieee802154/ca8210.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ieee802154/ca8210.c b/drivers/net/ieee802154/ca8210.c
index 753215ebc67c..154af346c936 100644
--- a/drivers/net/ieee802154/ca8210.c
+++ b/drivers/net/ieee802154/ca8210.c
@@ -597,7 +597,7 @@ static int ca8210_test_int_driver_write(
 	fifo_buffer = kmemdup(buf, len, GFP_KERNEL);
 	if (!fifo_buffer)
 		return -ENOMEM;
-	kfifo_in(&test->up_fifo, &fifo_buffer, 4);
+	kfifo_in(&test->up_fifo, &fifo_buffer, sizeof(fifo_buffer));
 	wake_up_interruptible(&priv->test.readq);
 
 	return 0;
@@ -2541,7 +2541,8 @@ static ssize_t ca8210_test_int_user_read(
 		);
 	}
 
-	if (kfifo_out(&priv->test.up_fifo, &fifo_buffer, 4) != 4) {
+	if (kfifo_out(&priv->test.up_fifo, &fifo_buffer, sizeof(fifo_buffer))
+	    != sizeof(fifo_buffer)) {
 		dev_err(
 			&priv->spi->dev,
 			"test_interface: Wrong number of elements popped from upstream fifo\n"
-- 
2.25.1