[PATCH] [ROSE] zero length frame filtering in af_rose.c

[Bernard Pidoux <bpidoux@free.fr>]

Since changeset e79ad711a0108475c1b3a03815527e7237020b08 from  mainline.
From: David S. Miller <davem@davemloft.net>
empty packet can be transmitted on connected socket for datagram protocols.

However, this patch broke a high level application using ROSE network 
protocole with connected datagram.

Bulletin Board Stations perform bulletins forwarding between BBS stations by  
radio and ROSE network using a forward protocole.
Now, if for some reason, a sending buffer in the application software happens 
to be empty at a specific moment, ROSE relays an empty packet via unfiltred 
packet socket.
When received, this ROSE packet introduces perturbations of BBS data 
forwarding protocole, for the application protocole is waiting for something 
else than an empty packet.
We agree that a more carefull programming of the application protocole would 
avoid this situation and we are willing to debug it.
But, as an empty frame is no use, and does not have any meaning for ROSE 
protocole, we may consider filtering zero length data both when sending and 
receiving socket data.

The proposed patch repairs BBS data exchange through ROSE network that were 
broken since 2.6.22.11 kernel.

Signed-off-by: Bernard Pidoux <f6bvp@amsat.org>
---
 net/rose/af_rose.c |   10 ++++++++++
 1 files changed, 10 insertions(+), 0 deletions(-)

diff --git a/net/rose/af_rose.c b/net/rose/af_rose.c
index 8a54cff..92af3a6 100644
--- a/net/rose/af_rose.c
+++ b/net/rose/af_rose.c
@@ -1075,6 +1075,10 @@ static int rose_sendmsg(struct kiocb *iocb, struct 
socket *sock,
        unsigned char *asmptr;
        int n, size, qbit = 0;
 
+       /* ROSE empty frame has no meaning : don't send */
+       if (len == 0)
+               return 0;
+
        if (msg->msg_flags & ~(MSG_DONTWAIT|MSG_EOR|MSG_CMSG_COMPAT))
                return -EINVAL;
 
@@ -1268,6 +1272,12 @@ static int rose_recvmsg(struct kiocb *iocb, struct 
socket *sock,
        skb_reset_transport_header(skb);
        copied     = skb->len;
 
+       /* ROSE empty frame has no meaning : ignore it */
+       if (copied == 0) {
+               skb_free_datagram(sk, skb);
+               return copied;
+       }
+
        if (copied > size) {
                copied = size;
                msg->msg_flags |= MSG_TRUNC;
-- 
1.5.5