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SubjectRe: [PATCH] net: 8390: Fix possible data races in __ei_get_stats
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On 2018/5/7 22:15, Eric Dumazet wrote:
>
> On 05/07/2018 07:08 AM, Jia-Ju Bai wrote:
>> The write operations to "dev->stats" are protected by
>> the spinlock on line 862-864, but the read operations to
>> this data on line 858 and 867 are not protected by the spinlock.
>> Thus, there may exist data races for "dev->stats".
>>
>> To fix the data races, the read operations to "dev->stats" are
>> protected by the spinlock, and a local variable is used for return.
>>
>> Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
>> ---
>> drivers/net/ethernet/8390/lib8390.c | 14 ++++++++++----
>> 1 file changed, 10 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/net/ethernet/8390/lib8390.c b/drivers/net/ethernet/8390/lib8390.c
>> index c9c55c9eab9f..198952247d30 100644
>> --- a/drivers/net/ethernet/8390/lib8390.c
>> +++ b/drivers/net/ethernet/8390/lib8390.c
>> @@ -852,19 +852,25 @@ static struct net_device_stats *__ei_get_stats(struct net_device *dev)
>> unsigned long ioaddr = dev->base_addr;
>> struct ei_device *ei_local = netdev_priv(dev);
>> unsigned long flags;
>> + struct net_device_stats *stats;
>> +
>> + spin_lock_irqsave(&ei_local->page_lock, flags);
>>
>> /* If the card is stopped, just return the present stats. */
>> - if (!netif_running(dev))
>> - return &dev->stats;
>> + if (!netif_running(dev)) {
>> + stats = &dev->stats;
>> + spin_unlock_irqrestore(&ei_local->page_lock, flags);
>> + return stats;
>> + }
>>
>> - spin_lock_irqsave(&ei_local->page_lock, flags);
>> /* Read the counter registers, assuming we are in page 0. */
>> dev->stats.rx_frame_errors += ei_inb_p(ioaddr + EN0_COUNTER0);
>> dev->stats.rx_crc_errors += ei_inb_p(ioaddr + EN0_COUNTER1);
>> dev->stats.rx_missed_errors += ei_inb_p(ioaddr + EN0_COUNTER2);
>> + stats = &dev->stats;
>> spin_unlock_irqrestore(&ei_local->page_lock, flags);
>>
>> - return &dev->stats;
>> + return stats;
>> }
>>
>> /*
>>
> dev->stats is not a pointer, it is an array embedded in the
> struct net_device
>
> So this patch is not needed, since dev->stats can not change.

Thanks for your reply :)

I do not understand that why "dev->stats can not change".
Its data is indeed changed by the code:
dev->stats.rx_frame_errors += ei_inb_p(ioaddr + EN0_COUNTER0);
dev->stats.rx_crc_errors += ei_inb_p(ioaddr + EN0_COUNTER1);
dev->stats.rx_missed_errors += ei_inb_p(ioaddr + EN0_COUNTER2);

So I think a data race may occur when returning "dev->stats" without
lock protection.

By the way, I find this possible data race is similar to the previous
commit 7b31b4deda76 for the tg3 driver.


Best wishes,
Jia-Ju Bai

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