[PATCH net-next 1/1] af-packet: fix - avoid reading stale data

[PATCH net-next 1/1] af-packet: fix - avoid reading stale data

[Chetan Loke]

Currently we flush tp_status and then flush the remainder of the header+payload.
tp_status should be flushed in the end to avoid stale data being read by user-space.


Signed-off-by: Chetan Loke <loke.chetan@gmail.com>
---
 net/packet/af_packet.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index d2294ad..f7be71f 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -1129,8 +1129,6 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
 	else
 		sll->sll_ifindex = dev->ifindex;
 
-	__packet_set_status(po, h.raw, status);
-	smp_mb();
 #if ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE == 1
 	{
 		u8 *start, *end;
@@ -1140,6 +1138,8 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
 			flush_dcache_page(pgv_to_page(start));
 	}
 #endif
+	smp_mb();
+	__packet_set_status(po, h.raw, status);
 
 	sk->sk_data_ready(sk, 0);
 
-- 
1.7.5.2

Re: [PATCH net-next 1/1] af-packet: fix - avoid reading stale data

[Eric Dumazet]

Le mardi 12 juillet 2011 à 21:42 -0400, Chetan Loke a écrit :
> Currently we flush tp_status and then flush the remainder of the header+payload.
> tp_status should be flushed in the end to avoid stale data being read by user-space.
> 
> 
> Signed-off-by: Chetan Loke <loke.chetan@gmail.com>
> ---
>  net/packet/af_packet.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
> index d2294ad..f7be71f 100644
> --- a/net/packet/af_packet.c
> +++ b/net/packet/af_packet.c
> @@ -1129,8 +1129,6 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
>  	else
>  		sll->sll_ifindex = dev->ifindex;
>  
> -	__packet_set_status(po, h.raw, status);
> -	smp_mb();
>  #if ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE == 1
>  	{
>  		u8 *start, *end;
> @@ -1140,6 +1138,8 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
>  			flush_dcache_page(pgv_to_page(start));
>  	}
>  #endif
> +	smp_mb();
> +	__packet_set_status(po, h.raw, status);
>  
>  	sk->sk_data_ready(sk, 0);
>  

Are you sure we can perform the flush_dcache_page() before smp_mb() ?

I believe we should do one smp_wmb() before __packet_set_status() as
well.

Re: [PATCH net-next 1/1] af-packet: fix - avoid reading stale data

[chetan loke]

On Tue, Jul 12, 2011 at 9:56 PM, Eric Dumazet <eric.dumazet@gmail.com> wrote:
> Le mardi 12 juillet 2011 à 21:42 -0400, Chetan Loke a écrit :
>> Currently we flush tp_status and then flush the remainder of the header+payload.
>> tp_status should be flushed in the end to avoid stale data being read by user-space.
>>
>>
>> Signed-off-by: Chetan Loke <loke.chetan@gmail.com>
>> ---
>>  net/packet/af_packet.c |    4 ++--
>>  1 files changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
>> index d2294ad..f7be71f 100644
>> --- a/net/packet/af_packet.c
>> +++ b/net/packet/af_packet.c
>> @@ -1129,8 +1129,6 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
>>       else
>>               sll->sll_ifindex = dev->ifindex;
>>
>> -     __packet_set_status(po, h.raw, status);
>> -     smp_mb();
>>  #if ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE == 1
>>       {
>>               u8 *start, *end;
>> @@ -1140,6 +1138,8 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
>>                       flush_dcache_page(pgv_to_page(start));
>>       }
>>  #endif
>> +     smp_mb();
>> +     __packet_set_status(po, h.raw, status);
>>
>>       sk->sk_data_ready(sk, 0);
>>
>
> Are you sure we can perform the flush_dcache_page() before smp_mb() ?
>
> I believe we should do one smp_wmb() before __packet_set_status() as
> well.

Eric - something like this?

#if ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE == 1
          smp_wmb();
#endif
__packet_set_status(po, h.raw, status);


Chetan Loke