From 64e6ba7f2d2f022469be6c2a1c179851b94842dc Mon Sep 17 00:00:00 2001 From: Ciara Loftus Date: Tue, 14 Jun 2022 07:07:46 +0000 Subject: [PATCH] xsk: Fix generic transmit when completion queue reservation fails [ Upstream commit a6e944f25cdbe6b82275402b8bc9a55ad7aac10b ] Two points of potential failure in the generic transmit function are: 1. completion queue (cq) reservation failure. 2. skb allocation failure Originally the cq reservation was performed first, followed by the skb allocation. Commit 675716400da6 ("xdp: fix possible cq entry leak") reversed the order because at the time there was no mechanism available to undo the cq reservation which could have led to possible cq entry leaks in the event of skb allocation failure. However if the skb allocation is performed first and the cq reservation then fails, the xsk skb destructor is called which blindly adds the skb address to the already full cq leading to undefined behavior. This commit restores the original order (cq reservation followed by skb allocation) and uses the xskq_prod_cancel helper to undo the cq reserve in event of skb allocation failure. Fixes: 675716400da6 ("xdp: fix possible cq entry leak") Signed-off-by: Ciara Loftus Signed-off-by: Daniel Borkmann Acked-by: Magnus Karlsson Link: https://lore.kernel.org/bpf/20220614070746.8871-1-ciara.loftus@intel.com Signed-off-by: Sasha Levin --- net/xdp/xsk.c | 16 +++++++++------- 1 file changed, 9 insertions(+), 7 deletions(-) diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c index 16cc38e..9b55ca2 100644 --- a/net/xdp/xsk.c +++ b/net/xdp/xsk.c @@ -553,12 +553,6 @@ static int xsk_generic_xmit(struct sock *sk) goto out; } - skb = xsk_build_skb(xs, &desc); - if (IS_ERR(skb)) { - err = PTR_ERR(skb); - goto out; - } - /* This is the backpressure mechanism for the Tx path. * Reserve space in the completion queue and only proceed * if there is space in it. This avoids having to implement @@ -567,11 +561,19 @@ static int xsk_generic_xmit(struct sock *sk) spin_lock_irqsave(&xs->pool->cq_lock, flags); if (xskq_prod_reserve(xs->pool->cq)) { spin_unlock_irqrestore(&xs->pool->cq_lock, flags); - kfree_skb(skb); goto out; } spin_unlock_irqrestore(&xs->pool->cq_lock, flags); + skb = xsk_build_skb(xs, &desc); + if (IS_ERR(skb)) { + err = PTR_ERR(skb); + spin_lock_irqsave(&xs->pool->cq_lock, flags); + xskq_prod_cancel(xs->pool->cq); + spin_unlock_irqrestore(&xs->pool->cq_lock, flags); + goto out; + } + err = __dev_direct_xmit(skb, xs->queue_id); if (err == NETDEV_TX_BUSY) { /* Tell user-space to retry the send */ -- 2.7.4