[PATCH net v2] netmem: prevent TX of unreadable skbs

[Mina Almasry]

Currently on stable trees we have support for netmem/devmem RX but not
TX. It is not safe to forward/redirect an RX unreadable netmem packet
into the device's TX path, as the device may call dma-mapping APIs on
dma addrs that should not be passed to it.

Fix this by preventing the xmit of unreadable skbs.

Tested by configuring tc redirect:

sudo tc qdisc add dev eth1 ingress
sudo tc filter add dev eth1 ingress protocol ip prio 1 flower ip_proto \
	tcp src_ip 192.168.1.12 action mirred egress redirect dev eth1

Before, I see unreadable skbs in the driver's TX path passed to dma
mapping APIs.

After, I don't see unreadable skbs in the driver's TX path passed to dma
mapping APIs.

Fixes: 65249feb6b3d ("net: add support for skbs with unreadable frags")
Suggested-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Mina Almasry <almasrymina@xxxxxxxxxx>

---

v2: https://lore.kernel.org/netdev/20250305191153.6d899a00@xxxxxxxxxx/

- Put unreadable check at the top (Jakub)
---
 net/core/dev.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/core/dev.c b/net/core/dev.c
index 30da277c5a6f..2f7f5fd9ffec 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3872,6 +3872,9 @@ static struct sk_buff *validate_xmit_skb(struct sk_buff *skb, struct net_device
 {
 	netdev_features_t features;
 
+	if (!skb_frags_readable(skb))
+		goto out_kfree_skb;
+
 	features = netif_skb_features(skb);
 	skb = validate_xmit_vlan(skb, features);
 	if (unlikely(!skb))

base-commit: f315296c92fd4b7716bdea17f727ab431891dc3b
-- 
2.49.0.rc0.332.g42c0ae87b1-goog