Commit 60034d3d authored Jul 30, 2019 by David Howells

rxrpc: Fix potential deadlock



There is a potential deadlock in rxrpc_peer_keepalive_dispatch() whereby
rxrpc_put_peer() is called with the peer_hash_lock held, but if it reduces
the peer's refcount to 0, rxrpc_put_peer() calls __rxrpc_put_peer() - which
the tries to take the already held lock.

Fix this by providing a version of rxrpc_put_peer() that can be called in
situations where the lock is already held.

The bug may produce the following lockdep report:

============================================
WARNING: possible recursive locking detected
5.2.0-next-20190718 #41 Not tainted
--------------------------------------------
kworker/0:3/21678 is trying to acquire lock:
00000000aa5eecdf (&(&rxnet->peer_hash_lock)->rlock){+.-.}, at: spin_lock_bh
/./include/linux/spinlock.h:343 [inline]
00000000aa5eecdf (&(&rxnet->peer_hash_lock)->rlock){+.-.}, at:
__rxrpc_put_peer /net/rxrpc/peer_object.c:415 [inline]
00000000aa5eecdf (&(&rxnet->peer_hash_lock)->rlock){+.-.}, at:
rxrpc_put_peer+0x2d3/0x6a0 /net/rxrpc/peer_object.c:435

but task is already holding lock:
00000000aa5eecdf (&(&rxnet->peer_hash_lock)->rlock){+.-.}, at: spin_lock_bh
/./include/linux/spinlock.h:343 [inline]
00000000aa5eecdf (&(&rxnet->peer_hash_lock)->rlock){+.-.}, at:
rxrpc_peer_keepalive_dispatch /net/rxrpc/peer_event.c:378 [inline]
00000000aa5eecdf (&(&rxnet->peer_hash_lock)->rlock){+.-.}, at:
rxrpc_peer_keepalive_worker+0x6b3/0xd02 /net/rxrpc/peer_event.c:430

Fixes: 330bdcfa ("rxrpc: Fix the keepalive generator [ver #2]")
Reported-by:  <syzbot+72af434e4b3417318f84@syzkaller.appspotmail.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Marc Dionne <marc.dionne@auristor.com>
Reviewed-by: Jeffrey Altman <jaltman@auristor.com>

parent a20961cc

net/rxrpc/ar-internal.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -1061,6 +1061,7 @@ void rxrpc_destroy_all_peers(struct rxrpc_net *);
		struct rxrpc_peer rxrpc_get_peer(struct rxrpc_peer );
		struct rxrpc_peer rxrpc_get_peer_maybe(struct rxrpc_peer );
		void rxrpc_put_peer(struct rxrpc_peer *);
		void rxrpc_put_peer_locked(struct rxrpc_peer *);

		/*
		* proc.c

net/rxrpc/peer_event.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -378,7 +378,7 @@ static void rxrpc_peer_keepalive_dispatch(struct rxrpc_net *rxnet,
		spin_lock_bh(&rxnet->peer_hash_lock);
		list_add_tail(&peer->keepalive_link,
		&rxnet->peer_keepalive[slot & mask]);
		rxrpc_put_peer(peer);
		rxrpc_put_peer_locked(peer);
		}

		spin_unlock_bh(&rxnet->peer_hash_lock);

net/rxrpc/peer_object.c

+18 −0

Original line number	Diff line number	Diff line
		@@ -436,6 +436,24 @@ void rxrpc_put_peer(struct rxrpc_peer *peer)
		}
		}

		/*
		* Drop a ref on a peer record where the caller already holds the
		* peer_hash_lock.
		*/
		void rxrpc_put_peer_locked(struct rxrpc_peer *peer)
		{
		const void *here = __builtin_return_address(0);
		int n;

		n = atomic_dec_return(&peer->usage);
		trace_rxrpc_peer(peer, rxrpc_peer_put, n, here);
		if (n == 0) {
		hash_del_rcu(&peer->hash_link);
		list_del_init(&peer->keepalive_link);
		kfree_rcu(peer, rcu);
		}
		}

		/*
		* Make sure all peer records have been discarded.
		*/

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