acpi_battery: avoid divide-by-zero when no devices have capacity info

On laptops with builtin batteries, disconnecting the battery may show up
as a battery without any capacity information. (The theory is that one
is disconnecting the cells but the electronics identifying the battery
are still connected.) As a result, the loop over all batteries in
acpi_battery_get_battinfo results in total_lfcap == 0.

So, just check that total_lfcap is non-zero to avoid a division by zero
(triggerable by sysctl hw.acpi.battery).

Reported by:	Stefano Marinelli
Tested by:	Stefano Marinelli
Reviewed by:	emaste
Differential Revision: https://reviews.freebsd.org/D44818

(cherry picked from commit 2e850b832f5d2adb9b230d191277d67c00caaab9)

1 files changed, 8 insertions, 1 deletions

diff --git a/sys/dev/acpica/acpi_battery.c b/sys/dev/acpica/acpi_battery.c
index 7455c6afc6a6..cfd8261d5eab 100644
--- a/sys/dev/acpica/acpi_battery.c
+++ b/sys/dev/acpica/acpi_battery.c
@@ -266,7 +266,14 @@ acpi_battery_get_battinfo(device_t dev, struct acpi_battinfo *battinfo)
      */
     if (valid_units > 0) {
 	if (dev == NULL) {
-	    battinfo->cap = (total_cap * 100) / total_lfcap;
+	    /*
+	     * Avoid division by zero if none of the batteries had valid
+	     * capacity info.
+	     */
+	    if (total_lfcap > 0)
+		battinfo->cap = (total_cap * 100) / total_lfcap;
+	    else
+		battinfo->cap = 0;
 	    battinfo->min = total_min;
 	    battinfo->state = batt_stat;
 	    battinfo->rate = valid_rate;