rxrpc: Fix incoming call setup race

An incoming call can race with rxrpc socket destruction, leading to a
leaked call.  This may result in an oops when the call timer eventually
expires:

   BUG: kernel NULL pointer dereference, address: 0000000000000874
   RIP: 0010:_raw_spin_lock_irqsave+0x2a/0x50
   Call Trace:
    <IRQ>
    try_to_wake_up+0x59/0x550
    ? __local_bh_enable_ip+0x37/0x80
    ? rxrpc_poke_call+0x52/0x110 [rxrpc]
    ? rxrpc_poke_call+0x110/0x110 [rxrpc]
    ? rxrpc_poke_call+0x110/0x110 [rxrpc]
    call_timer_fn+0x24/0x120

with a warning in the kernel log looking something like:

   rxrpc: Call 00000000ba5e571a still in use (1,SvAwtACK,1061d,0)!

incurred during rmmod of rxrpc.  The 1061d is the call flags:

   RECVMSG_READ_ALL, RX_HEARD, BEGAN_RX_TIMER, RX_LAST, EXPOSED,
   IS_SERVICE, RELEASED

but no DISCONNECTED flag (0x800), so it's an incoming (service) call and
it's still connected.

The race appears to be that:

 (1) rxrpc_new_incoming_call() consults the service struct, checks sk_state
     and allocates a call - then pauses, possibly for an interrupt.

 (2) rxrpc_release_sock() sets RXRPC_CLOSE, nulls the service pointer,
     discards the prealloc and releases all calls attached to the socket.

 (3) rxrpc_new_incoming_call() resumes, launching the new call, including
     its timer and attaching it to the socket.

Fix this by read-locking local->services_lock to access the AF_RXRPC socket
providing the service rather than RCU in rxrpc_new_incoming_call().
There's no real need to use RCU here as local->services_lock is only
write-locked by the socket side in two places: when binding and when
shutting down.

Fixes: 5e6ef4f1017c ("rxrpc: Make the I/O thread take over the call and local processor work")
Reported-by: Marc Dionne <marc.dionne@auristor.com>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: linux-afs@lists.infradead.org

1 files changed, 3 insertions, 3 deletions

diff --git a/net/rxrpc/security.c b/net/rxrpc/security.c
index cd66634dffe6..cb8dd1d3b1d4 100644
--- a/net/rxrpc/security.c
+++ b/net/rxrpc/security.c
@@ -178,9 +178,9 @@ struct key *rxrpc_look_up_server_security(struct rxrpc_connection *conn,
 		sprintf(kdesc, "%u:%u",
 			sp->hdr.serviceId, sp->hdr.securityIndex);
 
-	rcu_read_lock();
+	read_lock(&conn->local->services_lock);
 
-	rx = rcu_dereference(conn->local->service);
+	rx = conn->local->service;
 	if (!rx)
 		goto out;
 
@@ -202,6 +202,6 @@ struct key *rxrpc_look_up_server_security(struct rxrpc_connection *conn,
 	}
 
 out:
-	rcu_read_unlock();
+	read_unlock(&conn->local->services_lock);
 	return key;
 }