[PATCH net 4/4] xsk: drain continuation descs on invalid descriptor in __xsk_generic_xmit()

[Jason Xing <kerneljasonxing@gmail.com>]

From: Jason Xing <kernelxing@tencent.com>

When the TX loop in __xsk_generic_xmit() encounters an invalid
descriptor mid-packet (e.g. an out-of-bounds address), the partial
skb is dropped and the offending descriptor is released. However,
remaining continuation descriptors belonging to the same multi-buffer
packet still sit in the TX ring. Since xs->skb becomes NULL after the
drop, the next iteration treats the leftover continuation fragment as
a brand-new packet, corrupting the packet stream.

Fix this by setting the drain_cont flag when the released descriptor
has XDP_PKT_CONTD set. On the next call to __xsk_generic_xmit(), the
drain logic introduced in the previous patch handles the remaining
fragments with normal CQ backpressure.

Fixes: cf24f5a5feea ("xsk: add support for AF_XDP multi-buffer on Tx path")
Signed-off-by: Jason Xing <kernelxing@tencent.com>
---
 net/xdp/xsk.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
index 232dd7126905..b41ed44e3192 100644
--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c
@@ -1045,6 +1045,8 @@ static int __xsk_generic_xmit(struct sock *sk)
 		if (xs->skb)
 			xsk_drop_skb(xs->skb);
 		xskq_cons_release(xs->tx);
+		if (xp_mb_desc(&desc))
+			xs->drain_cont = true;
 	}
 
 out:
-- 
2.41.3