crimson/monc: don't serve auth requests without active mon connection.

It's yet another racing issue which happens when auth request
handling is performed during the `active_con` reset sequence.
It caused the following `nullptr` dereference at Sepia:

```
DEBUG 2021-06-09 10:27:24,059 [shard 0] ms - [osd.6(client) v2:172.21.15.170:6809/33397 >> client.? -@39840] GOT AuthRequestFrame: method=2, p
referred_modes={2, 1}, payload_len=174
/home/jenkins-build/build/workspace/ceph-dev-new-build/ARCH/x86_64/AVAILABLE_ARCH/x86_64/AVAILABLE_DIST/centos8/DIST/centos8/MACHINE_SIZE/gigantic/release/17.0.0-4977-g65cb255e/rpm/el8/BUILD/ceph-17.0.0-4977-g65cb255e/src/crimson/mon/MonClient.cc:595:26: runtime error: member call on null pointer of type 'struct Connection'
/home/jenkins-build/build/workspace/ceph-dev-new-build/ARCH/x86_64/AVAILABLE_ARCH/x86_64/AVAILABLE_DIST/centos8/DIST/centos8/MACHINE_SIZE/gigantic/release/17.0.0-4977-g65cb255e/rpm/el8/BUILD/ceph-17.0.0-4977-g65cb255e/src/crimson/mon/MonClient.cc:178:11: runtime error: member access within null pointer of type 'struct Connection'
Segmentation fault on shard 0.
Backtrace:
 0# 0x0000563F9C00395F in ceph-osd
 1# FatalSignal::signaled(int, siginfo_t const*) in ceph-osd
 2# FatalSignal::install_oneshot_signal_handler<11>()::{lambda(int, siginfo_t*, void*)#1}::_FUN(int, siginfo_t*, void*) in ceph-osd
 3# 0x00007F4A064D0B20 in /lib64/libpthread.so.0
 4# crimson::mon::Connection::get_keys() in ceph-osd
 5# crimson::mon::Client::handle_auth_request(seastar::shared_ptr<crimson::net::Connection>, seastar::lw_shared_ptr<AuthConnectionMeta>, bool, unsigned int, ceph::buffer::v15_2_0::list const&, ceph::buffer::v15_2_0::list*) in ceph-osd
 6# crimson::net::ProtocolV2::_handle_auth_request(ceph::buffer::v15_2_0::list&, bool) in ceph-osd
 7# 0x0000563F9D007B39 in ceph-osd
 8# 0x0000563F9D008C45 in ceph-osd
 9# 0x0000563F95FF8D70 in ceph-osd
10# 0x0000563FA1A560BF in ceph-osd
11# 0x0000563FA1A5B600 in ceph-osd
12# 0x0000563FA1C0D66B in ceph-osd
13# 0x0000563FA176B0EA in ceph-osd
14# 0x0000563FA177520E in ceph-osd
15# main in ceph-osd
16# __libc_start_main in /lib64/libc.so.6
17# _start in ceph-osd
Fault at location: 0xb0
```

Signed-off-by: Radoslaw Zarzynski <rzarzyns@redhat.com>

diff --git a/src/crimson/mon/MonClient.cc b/src/crimson/mon/MonClient.cc
index 64261865ce551ec5232a75bf4272c1aac62d9d2c..664ba9ce1468f92f22b0ca1498d811ad8512c764 100644 (file)
--- a/src/crimson/mon/MonClient.cc
+++ b/src/crimson/mon/MonClient.cc
@@ -587,6 +587,11 @@ int Client::handle_auth_request(crimson::net::ConnectionRef con,
     logger().info("skipping challenge on {}", con);
     authorizer_challenge = nullptr;
   }
+  if (!active_con) {
+    logger().info("auth request during inactivity period");
+    // let's instruct the client to come back later
+    return -EBUSY;
+  }
   bool was_challenge = (bool)auth_meta->authorizer_challenge;
   EntityName name;
   AuthCapsInfo caps_info;