From: Juergen Gross jgross@suse.com
commit 6032046ec4b70176d247a71836186d47b25d1684 upstream.
Commit 1d5d48523900a4b ("xen-netback: require fewer guest Rx slots when not using GSO") introduced a security problem in netback, as an interface would only be regarded to be stalled if no slot is available in the rx queue ring page. In case the SKB at the head of the queued requests will need more than one rx slot and only one slot is free the stall detection logic will never trigger, as the test for that is only looking for at least one slot to be free.
Fix that by testing for the needed number of slots instead of only one slot being available.
In order to not have to take the rx queue lock that often, store the number of needed slots in the queue data. As all SKB dequeue operations happen in the rx queue kernel thread this is safe, as long as the number of needed slots is accessed via READ/WRITE_ONCE() only and updates are always done with the rx queue lock held.
Add a small helper for obtaining the number of free slots.
This is part of XSA-392
Fixes: 1d5d48523900a4b ("xen-netback: require fewer guest Rx slots when not using GSO") Signed-off-by: Juergen Gross jgross@suse.com Reviewed-by: Jan Beulich jbeulich@suse.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/net/xen-netback/common.h | 1 drivers/net/xen-netback/rx.c | 65 ++++++++++++++++++++++++--------------- 2 files changed, 42 insertions(+), 24 deletions(-)
--- a/drivers/net/xen-netback/common.h +++ b/drivers/net/xen-netback/common.h @@ -203,6 +203,7 @@ struct xenvif_queue { /* Per-queue data unsigned int rx_queue_max; unsigned int rx_queue_len; unsigned long last_rx_time; + unsigned int rx_slots_needed; bool stalled;
struct xenvif_copy_state rx_copy; --- a/drivers/net/xen-netback/rx.c +++ b/drivers/net/xen-netback/rx.c @@ -33,28 +33,36 @@ #include <xen/xen.h> #include <xen/events.h>
-static bool xenvif_rx_ring_slots_available(struct xenvif_queue *queue) +/* + * Update the needed ring page slots for the first SKB queued. + * Note that any call sequence outside the RX thread calling this function + * needs to wake up the RX thread via a call of xenvif_kick_thread() + * afterwards in order to avoid a race with putting the thread to sleep. + */ +static void xenvif_update_needed_slots(struct xenvif_queue *queue, + const struct sk_buff *skb) { - RING_IDX prod, cons; - struct sk_buff *skb; - int needed; - unsigned long flags; + unsigned int needed = 0;
- spin_lock_irqsave(&queue->rx_queue.lock, flags); - - skb = skb_peek(&queue->rx_queue); - if (!skb) { - spin_unlock_irqrestore(&queue->rx_queue.lock, flags); - return false; + if (skb) { + needed = DIV_ROUND_UP(skb->len, XEN_PAGE_SIZE); + if (skb_is_gso(skb)) + needed++; + if (skb->sw_hash) + needed++; }
- needed = DIV_ROUND_UP(skb->len, XEN_PAGE_SIZE); - if (skb_is_gso(skb)) - needed++; - if (skb->sw_hash) - needed++; + WRITE_ONCE(queue->rx_slots_needed, needed); +}
- spin_unlock_irqrestore(&queue->rx_queue.lock, flags); +static bool xenvif_rx_ring_slots_available(struct xenvif_queue *queue) +{ + RING_IDX prod, cons; + unsigned int needed; + + needed = READ_ONCE(queue->rx_slots_needed); + if (!needed) + return false;
do { prod = queue->rx.sring->req_prod; @@ -80,6 +88,9 @@ void xenvif_rx_queue_tail(struct xenvif_
spin_lock_irqsave(&queue->rx_queue.lock, flags);
+ if (skb_queue_empty(&queue->rx_queue)) + xenvif_update_needed_slots(queue, skb); + __skb_queue_tail(&queue->rx_queue, skb);
queue->rx_queue_len += skb->len; @@ -100,6 +111,8 @@ static struct sk_buff *xenvif_rx_dequeue
skb = __skb_dequeue(&queue->rx_queue); if (skb) { + xenvif_update_needed_slots(queue, skb_peek(&queue->rx_queue)); + queue->rx_queue_len -= skb->len; if (queue->rx_queue_len < queue->rx_queue_max) { struct netdev_queue *txq; @@ -474,27 +487,31 @@ void xenvif_rx_action(struct xenvif_queu xenvif_rx_copy_flush(queue); }
-static bool xenvif_rx_queue_stalled(struct xenvif_queue *queue) +static RING_IDX xenvif_rx_queue_slots(const struct xenvif_queue *queue) { RING_IDX prod, cons;
prod = queue->rx.sring->req_prod; cons = queue->rx.req_cons;
+ return prod - cons; +} + +static bool xenvif_rx_queue_stalled(const struct xenvif_queue *queue) +{ + unsigned int needed = READ_ONCE(queue->rx_slots_needed); + return !queue->stalled && - prod - cons < 1 && + xenvif_rx_queue_slots(queue) < needed && time_after(jiffies, queue->last_rx_time + queue->vif->stall_timeout); }
static bool xenvif_rx_queue_ready(struct xenvif_queue *queue) { - RING_IDX prod, cons; - - prod = queue->rx.sring->req_prod; - cons = queue->rx.req_cons; + unsigned int needed = READ_ONCE(queue->rx_slots_needed);
- return queue->stalled && prod - cons >= 1; + return queue->stalled && xenvif_rx_queue_slots(queue) >= needed; }
bool xenvif_have_rx_work(struct xenvif_queue *queue, bool test_kthread)