netdev - [PATCH net 3/9] rxrpc: Fix NULL deref in rxrpc_unuse

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Date:   Thu, 15 Dec 2022 16:20:04 +0000
From:   David Howells <dhowells@...hat.com>
To:     netdev@...r.kernel.org
Cc:     syzbot+3538a6a72efa8b059c38@...kaller.appspotmail.com,
        syzbot+3538a6a72efa8b059c38@...kaller.appspotmail.com,
        Marc Dionne <marc.dionne@...istor.com>,
        linux-afs@...ts.infradead.org, dhowells@...hat.com,
        linux-afs@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH net 3/9] rxrpc: Fix NULL deref in rxrpc_unuse_local()

Fix rxrpc_unuse_local() to get the debug_id *after* checking to see if
local is NULL.

Fixes: a2cf3264f331 ("rxrpc: Fold __rxrpc_unuse_local() into rxrpc_unuse_local()")
Reported-by: syzbot+3538a6a72efa8b059c38@...kaller.appspotmail.com
Signed-off-by: David Howells <dhowells@...hat.com>
Tested-by: syzbot+3538a6a72efa8b059c38@...kaller.appspotmail.com
cc: Marc Dionne <marc.dionne@...istor.com>
cc: linux-afs@...ts.infradead.org
---

 net/rxrpc/local_object.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/rxrpc/local_object.c b/net/rxrpc/local_object.c
index 44222923c0d1..24ee585d9aaf 100644
--- a/net/rxrpc/local_object.c
+++ b/net/rxrpc/local_object.c
@@ -357,10 +357,11 @@ struct rxrpc_local *rxrpc_use_local(struct rxrpc_local *local,
  */
 void rxrpc_unuse_local(struct rxrpc_local *local, enum rxrpc_local_trace why)
 {
-	unsigned int debug_id = local->debug_id;
+	unsigned int debug_id;
 	int r, u;
 
 	if (local) {
+		debug_id = local->debug_id;
 		r = refcount_read(&local->ref);
 		u = atomic_dec_return(&local->active_users);
 		trace_rxrpc_local(debug_id, why, r, u);