[PATCH v3] Input: applespi - validate ACPI property buffer length

[Tristan Madani <tristmd@gmail.com>]

From: Tristan Madani <tristan@talencesecurity.com>

applespi_get_spi_settings() reads three ACPI _DSD properties
(spiCSDelay, resetA2RUsec, resetRecUsec) as u64 values from their
buffer pointers without verifying that the buffer is at least 8
bytes long.  If a firmware implementation provides a shorter buffer,
the u64 dereference reads beyond the allocated object.

Add buffer length checks before each u64 dereference.

Fixes: 038b1a05eae6 ("Input: add Apple SPI keyboard and trackpad driver")
Signed-off-by: Tristan Madani <tristan@talencesecurity.com>
---
Changes in v3:
- Drop Cc: stable since this is hardening rather than a fix for a
  specific regression, per Dmitry Torokhov

Changes in v2:
- Fix alignment of continued condition lines

 drivers/input/keyboard/applespi.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/input/keyboard/applespi.c b/drivers/input/keyboard/applespi.c
index cf25177b48301..db8947b5cf11c 100644
--- a/drivers/input/keyboard/applespi.c
+++ b/drivers/input/keyboard/applespi.c
@@ -642,19 +642,22 @@ static int applespi_get_spi_settings(struct applespi_data *applespi)
 	const union acpi_object *o;
 	struct spi_settings *settings = &applespi->spi_settings;
 
-	if (!acpi_dev_get_property(adev, "spiCSDelay", ACPI_TYPE_BUFFER, &o))
+	if (!acpi_dev_get_property(adev, "spiCSDelay", ACPI_TYPE_BUFFER, &o) &&
+	    o->buffer.length >= sizeof(u64))
 		settings->spi_cs_delay = *(u64 *)o->buffer.pointer;
 	else
 		dev_warn(&applespi->spi->dev,
 			 "Property spiCSDelay not found\n");
 
-	if (!acpi_dev_get_property(adev, "resetA2RUsec", ACPI_TYPE_BUFFER, &o))
+	if (!acpi_dev_get_property(adev, "resetA2RUsec", ACPI_TYPE_BUFFER, &o) &&
+	    o->buffer.length >= sizeof(u64))
 		settings->reset_a2r_usec = *(u64 *)o->buffer.pointer;
 	else
 		dev_warn(&applespi->spi->dev,
 			 "Property resetA2RUsec not found\n");
 
-	if (!acpi_dev_get_property(adev, "resetRecUsec", ACPI_TYPE_BUFFER, &o))
+	if (!acpi_dev_get_property(adev, "resetRecUsec", ACPI_TYPE_BUFFER, &o) &&
+	    o->buffer.length >= sizeof(u64))
 		settings->reset_rec_usec = *(u64 *)o->buffer.pointer;
 	else
 		dev_warn(&applespi->spi->dev,
-- 
2.47.3