[PATCH net 2/2] rxrpc: Fix bug due to prealloc collision

[David Howells]

When userspace is using AF_RXRPC to provide a server, it has to preallocate
incoming calls and assign to them call IDs that will be used to thread
related recvmsg() and sendmsg() together.  The preallocated call IDs will
automatically be attached to calls as they come in until the pool is empty.

To the kernel, the call IDs are just arbitrary numbers, but userspace can
use the call ID to hold a pointer to prepared structs.  In any case, the
user isn't permitted to create two calls with the same call ID (call IDs
become available again when the call ends) and EBADSLT should result from
sendmsg() if an attempt is made to preallocate a call with an in-use call
ID.

However, the cleanup in the error handling will trigger both assertions in
rxrpc_cleanup_call() because the call isn't marked complete and isn't
marked as having been released.

Fix this by setting the call state in rxrpc_service_prealloc_one() and then
marking it as being released before calling the cleanup function.

Fixes: 00e907127e6f ("rxrpc: Preallocate peers, conns and calls for incoming service requests")
Reported-by: Junvyyang, Tencent Zhuque Lab <zhuque at tencent.com>
Signed-off-by: David Howells <dhowells at redhat.com>
cc: LePremierHomme kwqcheii at proton.me
cc: Marc Dionne <marc.dionne at auristor.com>
cc: Jakub Kicinski <kuba at kernel.org>
cc: Paolo Abeni <pabeni at redhat.com>
cc: "David S. Miller" <davem at davemloft.net>
cc: Eric Dumazet <edumazet at google.com>
cc: Simon Horman <horms at kernel.org>
cc: linux-afs at lists.infradead.org
cc: netdev at vger.kernel.org
---
 net/rxrpc/call_accept.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/rxrpc/call_accept.c b/net/rxrpc/call_accept.c
index a4b363b47cca..32af666547f8 100644
--- a/net/rxrpc/call_accept.c
+++ b/net/rxrpc/call_accept.c
@@ -149,6 +149,8 @@ static int rxrpc_service_prealloc_one(struct rxrpc_sock *rx,
 
 id_in_use:
 	write_unlock(&rx->call_lock);
+	rxrpc_prefail_call(call, RXRPC_CALL_LOCAL_ERROR, -EBADSLT);
+	__set_bit(RXRPC_CALL_RELEASED, &call->flags);
 	rxrpc_cleanup_call(call);
 	_leave(" = -EBADSLT");
 	return -EBADSLT;