[PATCH bpf] xsk: Clear pool even for inactive queues

The number of queues can change by other means, rather than ethtool. For
example, attaching an mqprio qdisc with num_tc > 1 leads to creating
multiple sets of TX queues, which may be then destroyed when mqprio is
deleted. If an AF_XDP socket is created while mqprio is active,
dev->_tx[queue_id].pool will be filled, but then real_num_tx_queues may
decrease with deletion of mqprio, which will mean that the pool won't be
NULLed, and a further increase of the number of TX queues may expose a
dangling pointer.

To avoid any potential misbehavior, this commit clears pool for RX and
TX queues, regardless of real_num_*_queues, still taking into
consideration num_*_queues to avoid overflows.

Fixes: 1c1efc2af158 ("xsk: Create and free buffer pool independently from umem")
Fixes: a41b4f3c58dd ("xsk: simplify xdp_clear_umem_at_qid implementation")
Signed-off-by: Maxim Mikityanskiy <redacted>
---
 net/xdp/xsk.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
index 8037b04a9edd..4a83117507f5 100644
--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c

@@ -108,9 +108,9 @@ EXPORT_SYMBOL(xsk_get_pool_from_qid);
 
 void xsk_clear_pool_at_qid(struct net_device *dev, u16 queue_id)
 {
-	if (queue_id < dev->real_num_rx_queues)
+	if (queue_id < dev->num_rx_queues)
 		dev->_rx[queue_id].pool = NULL;
-	if (queue_id < dev->real_num_tx_queues)
+	if (queue_id < dev->num_tx_queues)
 		dev->_tx[queue_id].pool = NULL;
 }
 

-- 
2.25.1

Hello:

This patch was applied to bpf/bpf.git (refs/heads/master):

On Mon, 18 Jan 2021 18:03:33 +0200 you wrote:

The number of queues can change by other means, rather than ethtool. For
example, attaching an mqprio qdisc with num_tc > 1 leads to creating
multiple sets of TX queues, which may be then destroyed when mqprio is
deleted. If an AF_XDP socket is created while mqprio is active,
dev->_tx[queue_id].pool will be filled, but then real_num_tx_queues may
decrease with deletion of mqprio, which will mean that the pool won't be
NULLed, and a further increase of the number of TX queues may expose a
dangling pointer.

[...]

Here is the summary with links:
  - [bpf] xsk: Clear pool even for inactive queues
    https://git.kernel.org/bpf/bpf/c/b425e24a934e

You are awesome, thank you!
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On 2021-01-18 17:03, Maxim Mikityanskiy wrote:

The number of queues can change by other means, rather than ethtool. For
example, attaching an mqprio qdisc with num_tc > 1 leads to creating
multiple sets of TX queues, which may be then destroyed when mqprio is
deleted. If an AF_XDP socket is created while mqprio is active,
dev->_tx[queue_id].pool will be filled, but then real_num_tx_queues may
decrease with deletion of mqprio, which will mean that the pool won't be
NULLed, and a further increase of the number of TX queues may expose a
dangling pointer.

To avoid any potential misbehavior, this commit clears pool for RX and
TX queues, regardless of real_num_*_queues, still taking into
consideration num_*_queues to avoid overflows.

Fixes: 1c1efc2af158 ("xsk: Create and free buffer pool independently from umem")
Fixes: a41b4f3c58dd ("xsk: simplify xdp_clear_umem_at_qid implementation")
Signed-off-by: Maxim Mikityanskiy <redacted>

Thanks, Maxim!

Acked-by: Björn Töpel <redacted>