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power: supply: core: Fix boundary conditions in interpolation

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The functions power_supply_temp2resist_simple and power_supply_ocv2cap_simple
handle boundary conditions incorrectly.
The change was introduced in a4585ba205
("power: supply: core: Use library interpolation").
There are two issues: First, the lines "high = i - 1" and "high = i" in ocv2cap
have the wrong order compared to temp2resist. As a consequence, ocv2cap
sets high=-1 if ocv>table[0].ocv, which causes an out-of-bounds read.
Second, the logic of temp2resist is also not correct.
Consider the case table[] = {{20, 100}, {10, 80}, {0, 60}}.
For temp=5, we expect a resistance of 70% by interpolation.
However, temp2resist sets high=low=2 and returns 60.

Cc: stable@vger.kernel.org
Signed-off-by: Dorian Rudolph <mail@dorianrudolph.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Fixes: a4585ba205 ("power: supply: core: Use library interpolation")
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>
This commit is contained in:
Dorian Rudolph 2022-05-14 17:23:40 +02:00 committed by Sebastian Reichel
parent 80192eff64
commit 093d27bb6f
1 changed files with 12 additions and 12 deletions
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24
drivers/power/supply/power_supply_core.c
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@ -846,17 +846,17 @@ int power_supply_temp2resist_simple(struct power_supply_resistance_temp_table *t
{
int i, high, low;
/* Break loop at table_len - 1 because that is the highest index */
for (i = 0; i < table_len - 1; i++)
for (i = 0; i < table_len; i++)
if (temp > table[i].temp)
break;
/* The library function will deal with high == low */
if ((i == 0) || (i == (table_len - 1)))
high = i;
if (i == 0)
high = low = i;
else if (i == table_len)
high = low = i - 1;
else
high = i - 1;
low = i;
high = (low = i) - 1;
return fixp_linear_interpolate(table[low].temp,
table[low].resistance,
@ -958,17 +958,17 @@ int power_supply_ocv2cap_simple(struct power_supply_battery_ocv_table *table,
{
int i, high, low;
/* Break loop at table_len - 1 because that is the highest index */
for (i = 0; i < table_len - 1; i++)
for (i = 0; i < table_len; i++)
if (ocv > table[i].ocv)
break;
/* The library function will deal with high == low */
if ((i == 0) || (i == (table_len - 1)))
high = i - 1;
if (i == 0)
high = low = i;
else if (i == table_len)
high = low = i - 1;
else
high = i; /* i.e. i == 0 */
low = i;
high = (low = i) - 1;
return fixp_linear_interpolate(table[low].ocv,
table[low].capacity,