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Subjectsmall regression: hwmon: (applesmc) Check key count before proceeding - 5f4513864304672e6ea9eac60583eeac32e679f2
Hi Henrik & Guenther,

via commit 5f4513864304672e6ea9eac60583eeac32e679f2 the following
code was added:
diff --git a/drivers/hwmon/applesmc.c b/drivers/hwmon/applesmc.c
index 62c2e32..98814d1 100644
--- a/drivers/hwmon/applesmc.c
+++ b/drivers/hwmon/applesmc.c
@@ -525,16 +525,25 @@ static int applesmc_init_smcreg_try(void)
{
struct applesmc_registers *s = &smcreg;
bool left_light_sensor, right_light_sensor;
+ unsigned int count;
u8 tmp[1];
int ret;

if (s->init_complete)
return 0;

- ret = read_register_count(&s->key_count);
+ ret = read_register_count(&count);
if (ret)
return ret;

+ if (s->cache && s->key_count != count) {
+ pr_warn("key count changed from %d to %d\n",
+ s->key_count, count);
+ kfree(s->cache);
+ s->cache = NULL;
+ }
+ s->key_count = count;
+
if (!s->cache)
s->cache = kcalloc(s->key_count, sizeof(*s->cache),
GFP_KERNEL); if (!s->cache)

The issue Chris has seen in Fedora on one MacBookPro4,1
(https://bugzilla.redhat.com/show_bug.cgi?id=1033414) is that this
machine returns a huge number from read_register_count() so now we will
try to allocate an insane amount of memory and we will barf:
[ 8.603053] applesmc: key count changed from 261 to 1392508929
Dmidecode for this box is here:
https://bugzilla.redhat.com/attachment.cgi?id=828118

Do we need to special case this specific machine/smc version or should
we limit the kcalloc() call to a somewhat sane limit? Other thoughts?

Thanks,
Michele


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