rxrpc: Fix net namespace cleanup

In rxrpc_destroy_all_calls(), there are two phases: (1) make sure the
->calls list is empty, emitting error messages if not, and (2) wait for the
RCU cleanup to happen on outstanding calls (ie. ->nr_calls becomes 0).

To avoid taking the call_lock, the function prechecks ->calls and if empty,
it returns to avoid taking the lock - this is wrong, however: it still
needs to go and do the second phase and wait for ->nr_calls to become 0.

Without this, the rxrpc_net struct may get deallocated before we get to the
RCU cleanup for the last calls.  This can lead to:

  Slab corruption (Not tainted): kmalloc-16k start=ffff88802b178000, len=16384
  050: 6b 6b 6b 6b 6b 6b 6b 6b 61 6b 6b 6b 6b 6b 6b 6b  kkkkkkkkakkkkkkk

Note the "61" at offset 0x58.  This corresponds to the ->nr_calls member of
struct rxrpc_net (which is >9k in size, and thus allocated out of the 16k
slab).

Fix this by flipping the condition on the if-statement, putting the locked
section inside the if-body and dropping the return from there.  The
function will then always go on to wait for the RCU cleanup on outstanding
calls.

Fixes: 2baec2c3f854 ("rxrpc: Support network namespacing")
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 16 insertions, 16 deletions

diff --git a/net/rxrpc/call_object.c b/net/rxrpc/call_object.c
index 8aa2937b069f..fe96881a334d 100644
--- a/net/rxrpc/call_object.c
+++ b/net/rxrpc/call_object.c
@@ -604,30 +604,30 @@ void rxrpc_destroy_all_calls(struct rxrpc_net *rxnet)
 
         _enter("");
 
-        if (list_empty(&rxnet->calls))
-                return;
+        if (!list_empty(&rxnet->calls)) {
+                write_lock(&rxnet->call_lock);
 
-        write_lock(&rxnet->call_lock);
+                while (!list_empty(&rxnet->calls)) {
+                        call = list_entry(rxnet->calls.next,
+                                          struct rxrpc_call, link);
+                        _debug("Zapping call %p", call);
 
-        while (!list_empty(&rxnet->calls)) {
-                call = list_entry(rxnet->calls.next, struct rxrpc_call, link);
-                _debug("Zapping call %p", call);
+                        rxrpc_see_call(call);
+                        list_del_init(&call->link);
 
-                rxrpc_see_call(call);
-                list_del_init(&call->link);
+                        pr_err("Call %p still in use (%d,%s,%lx,%lx)!\n",
+                               call, atomic_read(&call->usage),
+                               rxrpc_call_states[call->state],
+                               call->flags, call->events);
 
-                pr_err("Call %p still in use (%d,%s,%lx,%lx)!\n",
-                       call, atomic_read(&call->usage),
-                       rxrpc_call_states[call->state],
-                       call->flags, call->events);
+                        write_unlock(&rxnet->call_lock);
+                        cond_resched();
+                        write_lock(&rxnet->call_lock);
+                }
 
                 write_unlock(&rxnet->call_lock);
-                cond_resched();
-                write_lock(&rxnet->call_lock);
         }
 
-        write_unlock(&rxnet->call_lock);
-
         atomic_dec(&rxnet->nr_calls);
         wait_var_event(&rxnet->nr_calls, !atomic_read(&rxnet->nr_calls));
 }