From f09ced4053bc0a2094a12b60b646114c966ef4c6 Mon Sep 17 00:00:00 2001 From: Magnus Karlsson Date: Fri, 18 Dec 2020 14:45:24 +0100 Subject: xsk: Fix race in SKB mode transmit with shared cq MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Fix a race when multiple sockets are simultaneously calling sendto() when the completion ring is shared in the SKB case. This is the case when you share the same netdev and queue id through the XDP_SHARED_UMEM bind flag. The problem is that multiple processes can be in xsk_generic_xmit() and call the backpressure mechanism in xskq_prod_reserve(xs->pool->cq). As this is a shared resource in this specific scenario, a race might occur since the rings are single-producer single-consumer. Fix this by moving the tx_completion_lock from the socket to the pool as the pool is shared between the sockets that share the completion ring. (The pool is not shared when this is not the case.) And then protect the accesses to xskq_prod_reserve() with this lock. The tx_completion_lock is renamed cq_lock to better reflect that it protects accesses to the potentially shared completion ring. Fixes: 35fcde7f8deb ("xsk: support for Tx") Reported-by: Xuan Zhuo Signed-off-by: Magnus Karlsson Signed-off-by: Daniel Borkmann Acked-by: Björn Töpel Link: https://lore.kernel.org/bpf/20201218134525.13119-2-magnus.karlsson@gmail.com --- include/net/xsk_buff_pool.h | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'include/net/xsk_buff_pool.h') diff --git a/include/net/xsk_buff_pool.h b/include/net/xsk_buff_pool.h index 01755b838c74..eaa8386dbc63 100644 --- a/include/net/xsk_buff_pool.h +++ b/include/net/xsk_buff_pool.h @@ -73,6 +73,11 @@ struct xsk_buff_pool { bool dma_need_sync; bool unaligned; void *addrs; + /* Mutual exclusion of the completion ring in the SKB mode. Two cases to protect: + * NAPI TX thread and sendmsg error paths in the SKB destructor callback and when + * sockets share a single cq when the same netdev and queue id is shared. + */ + spinlock_t cq_lock; struct xdp_buff_xsk *free_heads[]; }; -- cgit v1.2.3