[PATCH net] rxrpc: Fix local refcounting

* [PATCH net] rxrpc: Fix local refcounting
@ 2019-08-09 21:47 David Howells
  2019-08-09 22:34 ` Jeffrey E Altman
  2019-08-12  4:29 ` David Miller
  0 siblings, 2 replies; 3+ messages in thread
From: David Howells @ 2019-08-09 21:47 UTC (permalink / raw)
  To: netdev; +Cc: dhowells, jaltman, linux-afs, linux-kernel

Fix rxrpc_unuse_local() to handle a NULL local pointer as it can be called
on an unbound socket on which rx->local is not yet set.

The following reproduced (includes omitted):

	int main(void)
	{
		socket(AF_RXRPC, SOCK_DGRAM, AF_INET);
		return 0;
	}

causes the following oops to occur:

	BUG: kernel NULL pointer dereference, address: 0000000000000010
	...
	RIP: 0010:rxrpc_unuse_local+0x8/0x1b
	...
	Call Trace:
	 rxrpc_release+0x2b5/0x338
	 __sock_release+0x37/0xa1
	 sock_close+0x14/0x17
	 __fput+0x115/0x1e9
	 task_work_run+0x72/0x98
	 do_exit+0x51b/0xa7a
	 ? __context_tracking_exit+0x4e/0x10e
	 do_group_exit+0xab/0xab
	 __x64_sys_exit_group+0x14/0x17
	 do_syscall_64+0x89/0x1d4
	 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Reported-by: syzbot+20dee719a2e090427b5f@syzkaller.appspotmail.com
Fixes: 730c5fd42c1e ("rxrpc: Fix local endpoint refcounting")
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jeffrey Altman <jaltman@auristor.com>
---

 net/rxrpc/local_object.c |   12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/net/rxrpc/local_object.c b/net/rxrpc/local_object.c
index 9798159ee65f..c9db3e762d8d 100644
--- a/net/rxrpc/local_object.c
+++ b/net/rxrpc/local_object.c
@@ -402,11 +402,13 @@ void rxrpc_unuse_local(struct rxrpc_local *local)
 {
 	unsigned int au;
 
-	au = atomic_dec_return(&local->active_users);
-	if (au == 0)
-		rxrpc_queue_local(local);
-	else
-		rxrpc_put_local(local);
+	if (local) {
+		au = atomic_dec_return(&local->active_users);
+		if (au == 0)
+			rxrpc_queue_local(local);
+		else
+			rxrpc_put_local(local);
+	}
 }
 
 /*


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