From: Ciara Loftus ciara.loftus@intel.com
[ 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 ciara.loftus@intel.com Signed-off-by: Daniel Borkmann daniel@iogearbox.net Acked-by: Magnus Karlsson magnus.karlsson@intel.com Link: https://lore.kernel.org/bpf/20220614070746.8871-1-ciara.loftus@intel.com Signed-off-by: Sasha Levin sashal@kernel.org --- 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 d6bcdbfd0fc5..9b12ea3ab85a 100644 --- a/net/xdp/xsk.c +++ b/net/xdp/xsk.c @@ -538,12 +538,6 @@ 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 @@ -552,11 +546,19 @@ 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 */