[Qemu-devel] [PATCH] [slirp] Make ARP replies at least 64 bytes long

[Qemu-devel] [PATCH] [slirp] Make ARP replies at least 64 bytes long

[Hervé Poussineau]

IEEE 802.3 standard requires Ethernet frames to be at least 64 bytes long.
If it is not the case, they will be considered as runt frames, and may be ignored by netcard and/or OS

Signed-off-by: Hervé Poussineau <hpoussin@reactos.org>
---
 slirp/slirp.c |   12 ++++++++----
 1 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/slirp/slirp.c b/slirp/slirp.c
index 82fd9b4..2e8c017 100644
--- a/slirp/slirp.c
+++ b/slirp/slirp.c
@@ -599,9 +599,12 @@ static void arp_input(Slirp *slirp, const uint8_t *pkt, int pkt_len)
 {
     struct ethhdr *eh = (struct ethhdr *)pkt;
     struct arphdr *ah = (struct arphdr *)(pkt + ETH_HLEN);
-    uint8_t arp_reply[ETH_HLEN + sizeof(struct arphdr)];
-    struct ethhdr *reh = (struct ethhdr *)arp_reply;
-    struct arphdr *rah = (struct arphdr *)(arp_reply + ETH_HLEN);
+    union {
+        uint8_t data[ETH_HLEN + sizeof(struct arphdr)];
+        uint8_t payload[64]; /* Minimum Ethernet frame size */
+    } arp_reply;
+    struct ethhdr *reh = (struct ethhdr *)arp_reply.data;
+    struct arphdr *rah = (struct arphdr *)(arp_reply.data + ETH_HLEN);
     int ar_op;
     struct ex_list *ex_ptr;
 
@@ -619,6 +622,7 @@ static void arp_input(Slirp *slirp, const uint8_t *pkt, int pkt_len)
             }
             return;
         arp_ok:
+            memset(&arp_reply, 0, sizeof(arp_reply));
             /* XXX: make an ARP request to have the client address */
             memcpy(slirp->client_ethaddr, eh->h_source, ETH_ALEN);
 
@@ -637,7 +641,7 @@ static void arp_input(Slirp *slirp, const uint8_t *pkt, int pkt_len)
             rah->ar_sip = ah->ar_tip;
             memcpy(rah->ar_tha, ah->ar_sha, ETH_ALEN);
             rah->ar_tip = ah->ar_sip;
-            slirp_output(slirp->opaque, arp_reply, sizeof(arp_reply));
+            slirp_output(slirp->opaque, (const uint8_t *)&arp_reply, sizeof(arp_reply));
         }
         break;
     case ARPOP_REPLY:
-- 
1.7.1.GIT

Re: [Qemu-devel] [PATCH] [slirp] Make ARP replies at least 64 bytes long

[Edgar E. Iglesias]

On Mon, Sep 13, 2010 at 11:02:42PM +0200, Hervé Poussineau wrote:
> IEEE 802.3 standard requires Ethernet frames to be at least 64 bytes long.
> If it is not the case, they will be considered as runt frames, and may be ignored by netcard and/or OS
> 
> Signed-off-by: Hervé Poussineau <hpoussin@reactos.org>
> ---
>  slirp/slirp.c |   12 ++++++++----
>  1 files changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/slirp/slirp.c b/slirp/slirp.c
> index 82fd9b4..2e8c017 100644
> --- a/slirp/slirp.c
> +++ b/slirp/slirp.c
> @@ -599,9 +599,12 @@ static void arp_input(Slirp *slirp, const uint8_t *pkt, int pkt_len)
>  {
>      struct ethhdr *eh = (struct ethhdr *)pkt;
>      struct arphdr *ah = (struct arphdr *)(pkt + ETH_HLEN);
> -    uint8_t arp_reply[ETH_HLEN + sizeof(struct arphdr)];
> -    struct ethhdr *reh = (struct ethhdr *)arp_reply;
> -    struct arphdr *rah = (struct arphdr *)(arp_reply + ETH_HLEN);
> +    union {
> +        uint8_t data[ETH_HLEN + sizeof(struct arphdr)];
> +        uint8_t payload[64]; /* Minimum Ethernet frame size */
> +    } arp_reply;
> +    struct ethhdr *reh = (struct ethhdr *)arp_reply.data;
> +    struct arphdr *rah = (struct arphdr *)(arp_reply.data + ETH_HLEN);


Hi,

Would you mind explaning the point of the union here? Why not just
do something like:

-    uint8_t arp_reply[ETH_HLEN + sizeof(struct arphdr)];
+    uint8_t arp_reply[MAX(ETH_HLEN + sizeof(struct arphdr), 64)];

Cheers


>      int ar_op;
>      struct ex_list *ex_ptr;
>  
> @@ -619,6 +622,7 @@ static void arp_input(Slirp *slirp, const uint8_t *pkt, int pkt_len)
>              }
>              return;
>          arp_ok:
> +            memset(&arp_reply, 0, sizeof(arp_reply));
>              /* XXX: make an ARP request to have the client address */
>              memcpy(slirp->client_ethaddr, eh->h_source, ETH_ALEN);
>  
> @@ -637,7 +641,7 @@ static void arp_input(Slirp *slirp, const uint8_t *pkt, int pkt_len)
>              rah->ar_sip = ah->ar_tip;
>              memcpy(rah->ar_tha, ah->ar_sha, ETH_ALEN);
>              rah->ar_tip = ah->ar_sip;
> -            slirp_output(slirp->opaque, arp_reply, sizeof(arp_reply));
> +            slirp_output(slirp->opaque, (const uint8_t *)&arp_reply, sizeof(arp_reply));
>          }
>          break;
>      case ARPOP_REPLY:
> -- 
> 1.7.1.GIT
> 
> 

Re: [Qemu-devel] [PATCH] [slirp] Make ARP replies at least 64 bytes long

[Hervé Poussineau]

Edgar E. Iglesias a écrit :
> On Mon, Sep 13, 2010 at 11:02:42PM +0200, Hervé Poussineau wrote:
>   
>> IEEE 802.3 standard requires Ethernet frames to be at least 64 bytes long.
>> If it is not the case, they will be considered as runt frames, and may be ignored by netcard and/or OS
>>
>> Signed-off-by: Hervé Poussineau <hpoussin@reactos.org>
>> ---
>>  slirp/slirp.c |   12 ++++++++----
>>  1 files changed, 8 insertions(+), 4 deletions(-)
>>
>> diff --git a/slirp/slirp.c b/slirp/slirp.c
>> index 82fd9b4..2e8c017 100644
>> --- a/slirp/slirp.c
>> +++ b/slirp/slirp.c
>> @@ -599,9 +599,12 @@ static void arp_input(Slirp *slirp, const uint8_t *pkt, int pkt_len)
>>  {
>>      struct ethhdr *eh = (struct ethhdr *)pkt;
>>      struct arphdr *ah = (struct arphdr *)(pkt + ETH_HLEN);
>> -    uint8_t arp_reply[ETH_HLEN + sizeof(struct arphdr)];
>> -    struct ethhdr *reh = (struct ethhdr *)arp_reply;
>> -    struct arphdr *rah = (struct arphdr *)(arp_reply + ETH_HLEN);
>> +    union {
>> +        uint8_t data[ETH_HLEN + sizeof(struct arphdr)];
>> +        uint8_t payload[64]; /* Minimum Ethernet frame size */
>> +    } arp_reply;
>> +    struct ethhdr *reh = (struct ethhdr *)arp_reply.data;
>> +    struct arphdr *rah = (struct arphdr *)(arp_reply.data + ETH_HLEN);
>>     
>
>
> Hi,
>
> Would you mind explaning the point of the union here? Why not just
> do something like:
>
> -    uint8_t arp_reply[ETH_HLEN + sizeof(struct arphdr)];
> +    uint8_t arp_reply[MAX(ETH_HLEN + sizeof(struct arphdr), 64)];
>
>   
Good idea. I'll send an updated patch soon.

Hervé