The quad8_action_read() function checks the Count function mode and Count direction without first acquiring a lock. This is a race condition because the function mode could change by the time the direction is checked.
Because the quad8_function_read() already acquires a lock internally, the quad8_function_read() is refactored to spin out the no-lock code to a new quad8_function_get() function.
To resolve the race condition in quad8_action_read(), a lock is acquired before calling quad8_function_get() and quad8_direction_read() in order to get both function mode and direction atomically.
Fixes: f1d8a071d45b ("counter: 104-quad-8: Add Generic Counter interface support") Cc: stable@vger.kernel.org Signed-off-by: William Breathitt Gray william.gray@linaro.org --- drivers/counter/104-quad-8.c | 64 +++++++++++++++++++++++------------- 1 file changed, 42 insertions(+), 22 deletions(-)
diff --git a/drivers/counter/104-quad-8.c b/drivers/counter/104-quad-8.c index 77a863b7eefe..deed4afadb29 100644 --- a/drivers/counter/104-quad-8.c +++ b/drivers/counter/104-quad-8.c @@ -232,34 +232,45 @@ static const enum counter_function quad8_count_functions_list[] = { COUNTER_FUNCTION_QUADRATURE_X4, };
+static int quad8_function_get(const struct quad8 *const priv, const size_t id, + enum counter_function *const function) +{ + if (!priv->quadrature_mode[id]) { + *function = COUNTER_FUNCTION_PULSE_DIRECTION; + return 0; + } + + switch (priv->quadrature_scale[id]) { + case 0: + *function = COUNTER_FUNCTION_QUADRATURE_X1_A; + return 0; + case 1: + *function = COUNTER_FUNCTION_QUADRATURE_X2_A; + return 0; + case 2: + *function = COUNTER_FUNCTION_QUADRATURE_X4; + return 0; + default: + /* should never reach this path */ + return -EINVAL; + } +} + static int quad8_function_read(struct counter_device *counter, struct counter_count *count, enum counter_function *function) { struct quad8 *const priv = counter_priv(counter); - const int id = count->id; unsigned long irqflags; + int retval;
spin_lock_irqsave(&priv->lock, irqflags);
- if (priv->quadrature_mode[id]) - switch (priv->quadrature_scale[id]) { - case 0: - *function = COUNTER_FUNCTION_QUADRATURE_X1_A; - break; - case 1: - *function = COUNTER_FUNCTION_QUADRATURE_X2_A; - break; - case 2: - *function = COUNTER_FUNCTION_QUADRATURE_X4; - break; - } - else - *function = COUNTER_FUNCTION_PULSE_DIRECTION; + retval = quad8_function_get(priv, count->id, function);
spin_unlock_irqrestore(&priv->lock, irqflags);
- return 0; + return retval; }
static int quad8_function_write(struct counter_device *counter, @@ -359,6 +370,7 @@ static int quad8_action_read(struct counter_device *counter, enum counter_synapse_action *action) { struct quad8 *const priv = counter_priv(counter); + unsigned long irqflags; int err; enum counter_function function; const size_t signal_a_id = count->synapses[0].signal->id; @@ -374,9 +386,21 @@ static int quad8_action_read(struct counter_device *counter, return 0; }
- err = quad8_function_read(counter, count, &function); - if (err) + spin_lock_irqsave(&priv->lock, irqflags); + + /* Get Count function and direction atomically */ + err = quad8_function_get(priv, count->id, &function); + if (err) { + spin_unlock_irqrestore(&priv->lock, irqflags); + return err; + } + err = quad8_direction_read(counter, count, &direction); + if (err) { + spin_unlock_irqrestore(&priv->lock, irqflags); return err; + } + + spin_unlock_irqrestore(&priv->lock, irqflags);
/* Default action mode */ *action = COUNTER_SYNAPSE_ACTION_NONE; @@ -389,10 +413,6 @@ static int quad8_action_read(struct counter_device *counter, return 0; case COUNTER_FUNCTION_QUADRATURE_X1_A: if (synapse->signal->id == signal_a_id) { - err = quad8_direction_read(counter, count, &direction); - if (err) - return err; - if (direction == COUNTER_COUNT_DIRECTION_FORWARD) *action = COUNTER_SYNAPSE_ACTION_RISING_EDGE; else