Re: [PATCH V4 6/6] i2c: tegra: remove BUG, BUG_ON

Dmitry Osipenko
2019-06-10T18:18:16Z

10.06.2019 21:12, Dmitry Osipenko пишет:
> 10.06.2019 20:08, Bitan Biswas пишет:
>> Remove redundant BUG_ON calls or replace with WARN_ON_ONCE
>> as needed. Remove BUG() and make Rx and Tx case handling
>> similar.
>>
>> Signed-off-by: Bitan Biswas <bbiswas@nvidia.com>
>> ---
>> drivers/i2c/busses/i2c-tegra.c | 11 ++++++-----
>> 1 file changed, 6 insertions(+), 5 deletions(-)
>
> Looks that this is still not correct. What if it transfer-complete flag
> is set and buffer is full on RX? In this case the transfer will succeed
> while it was a failure.
>
>> diff --git a/drivers/i2c/busses/i2c-tegra.c b/drivers/i2c/busses/i2c-tegra.c
>> index 4dfb4c1..30619d6 100644
>> --- a/drivers/i2c/busses/i2c-tegra.c
>> +++ b/drivers/i2c/busses/i2c-tegra.c
>> @@ -515,7 +515,6 @@ static int tegra_i2c_empty_rx_fifo(struct tegra_i2c_dev *i2c_dev)
>> * prevent overwriting past the end of buf
>> */
>> if (rx_fifo_avail > 0 && buf_remaining > 0) {
>> - BUG_ON(buf_remaining > 3);
>
> Actually error should be returned here since out-of-bounds memory
> accesses must be avoided, hence:
>
> if (WARN_ON_ONCE(buf_remaining > 3))
> return -EINVAL;
>
>> val = i2c_readl(i2c_dev, I2C_RX_FIFO);
>> val = cpu_to_le32(val);
>> memcpy(buf, &val, buf_remaining);
>> @@ -523,7 +522,6 @@ static int tegra_i2c_empty_rx_fifo(struct tegra_i2c_dev *i2c_dev)
>> rx_fifo_avail--;
>> }
>>
>> - BUG_ON(rx_fifo_avail > 0 && buf_remaining > 0);
>
> Better not to ignore this as well:
>
> if (WARN_ON_ONCE(rx_fifo_avail > 0 &&
> buf_remaining > 0))
> return -EINVAL;
>
>> i2c_dev->msg_buf_remaining = buf_remaining;
>> i2c_dev->msg_buf = buf;
>>
>> @@ -581,7 +579,6 @@ static int tegra_i2c_fill_tx_fifo(struct tegra_i2c_dev *i2c_dev)
>> * boundary and fault.
>> */
>> if (tx_fifo_avail > 0 && buf_remaining > 0) {
>> - BUG_ON(buf_remaining > 3);
>
> And here, cause this will corrupt stack:
>
> if (WARN_ON_ONCE(buf_remaining > 3))
> return -EINVAL;
>
>> memcpy(&val, buf, buf_remaining);
>> val = le32_to_cpu(val);
>>
>> @@ -850,7 +847,8 @@ static irqreturn_t tegra_i2c_isr(int irq, void *dev_id)
>> if (i2c_dev->msg_buf_remaining)
>> tegra_i2c_empty_rx_fifo(i2c_dev);
>> else
>> - BUG();
>> + tegra_i2c_mask_irq(i2c_dev,
>> + I2C_INT_RX_FIFO_DATA_REQ);
>
> Then here:
>
> if (WARN_ON_ONCE(!i2c_dev->msg_buf_remaining) ||

Also note that this check could be moved out to the beginning of
tegra_i2c_empty_rx_fifo().