[PATCH 4.9 096/177] rxrpc: Ignore BUSY packets on old calls

From: Greg Kroah-Hartman
Date: Mon Dec 18 2017 - 12:17:17 EST

4.9-stable review patch. If anyone has any objections, please let me know.


From: David Howells <dhowells@xxxxxxxxxx>

[ Upstream commit 4d4a6ac73e7466c2085c307fac41f74ce4568a45 ]

If we receive a BUSY packet for a call we think we've just completed, the
packet is handed off to the connection processor to deal with - but the
connection processor doesn't expect a BUSY packet and so flags a protocol

Fix this by simply ignoring the BUSY packet for the moment.

The symptom of this may appear as a system call failing with EPROTO. This
may be triggered by pressing ctrl-C under some circumstances.

This comes about we abort calls due to interruption by a signal (which we
shouldn't do, but that's going to be a large fix and mostly in fs/afs/).
What happens is that we abort the call and may also abort follow up calls
too (this needs offloading somehoe). So we see a transmission of something
like the following sequence of packets:

DATA for call N
ABORT call N
DATA for call N+1
ABORT call N+1

in very quick succession on the same channel. However, the peer may have
deferred the processing of the ABORT from the call N to a background thread
and thus sees the DATA message from the call N+1 coming in before it has
cleared the channel. Thus it sends a BUSY packet[*].

[*] Note that some implementations (OpenAFS, for example) mark the BUSY
packet with one plus the callNumber of the call prior to call N.
Ordinarily, this would be call N, but there's no requirement for the
calls on a channel to be numbered strictly sequentially (the number is
required to increase).

This is wrong and means that the callNumber in the BUSY packet should
be ignored (it really ought to be N+1 since that's what it's in
response to).

Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
net/rxrpc/conn_event.c | 4 ++++
1 file changed, 4 insertions(+)

--- a/net/rxrpc/conn_event.c
+++ b/net/rxrpc/conn_event.c
@@ -275,6 +275,10 @@ static int rxrpc_process_event(struct rx
rxrpc_conn_retransmit_call(conn, skb);
return 0;

+ /* Just ignore BUSY packets for now. */
+ return 0;
if (skb_copy_bits(skb, sizeof(struct rxrpc_wire_header),
&wtmp, sizeof(wtmp)) < 0)