[PATCH 5.5 016/367] rxrpc: Fix use-after-free in rxrpc_put_local()

Greg Kroah-Hartman
2020-02-10T13:09:41Z

From: David Howells <dhowells@redhat.com>

[ Upstream commit fac20b9e738523fc884ee3ea5be360a321cd8bad ]

Fix rxrpc_put_local() to not access local->debug_id after calling
atomic_dec_return() as, unless that returned n==0, we no longer have the
right to access the object.

Fixes: 06d9532fa6b3 ("rxrpc: Fix read-after-free in rxrpc_queue_local()")
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/rxrpc/local_object.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

--- a/net/rxrpc/local_object.c
+++ b/net/rxrpc/local_object.c
@@ -364,11 +364,14 @@ void rxrpc_queue_local(struct rxrpc_loca
void rxrpc_put_local(struct rxrpc_local *local)
{
const void *here = __builtin_return_address(0);
+ unsigned int debug_id;
int n;

if (local) {
+ debug_id = local->debug_id;
+
n = atomic_dec_return(&local->usage);
- trace_rxrpc_local(local->debug_id, rxrpc_local_put, n, here);
+ trace_rxrpc_local(debug_id, rxrpc_local_put, n, here);

if (n == 0)
call_rcu(&local->rcu, rxrpc_local_rcu);