[PATCH 2/2 V3] applesmc: Perform some more sanity checking on temperatures

[Matthew Garrett <mjg@redhat.com>]

It seems that the two-byte temperature format is intended to be signed
("sp78" appears to mean "signed, decimal point, 7 bits before, 8 bits
after") and it doesn't seem terribly plausible that we'll get any of these
machines below freezing. It's probably more reasonable to assume that
negative values indicate errors and drop them.

Signed-off-by: Matthew Garrett <mjg@redhat.com>
---
 drivers/hwmon/applesmc.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/drivers/hwmon/applesmc.c b/drivers/hwmon/applesmc.c
index 851a685..411a627 100644
--- a/drivers/hwmon/applesmc.c
+++ b/drivers/hwmon/applesmc.c
@@ -744,6 +744,10 @@ static ssize_t applesmc_show_temperature(struct device *dev,
 		return ret;
 
 	if (entry->len == 2) {
+		if (buffer[0] >= 0x80) {
+			/* The two byte format is signed - ignore negative */
+			return -EINVAL;
+		}
 		temp = buffer[0] * 1000;
 		temp += (buffer[1] >> 6) * 250;
 	} else {
-- 
1.7.3.3