[PATCH net v1] netmem: prevent TX of unreadable skbs

[PATCH net v1] 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@kernel.org>
Cc: stable@vger.kernel.org
Signed-off-by: Mina Almasry <almasrymina@google.com>
---
 net/core/dev.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/core/dev.c b/net/core/dev.c
index 30da277c5a6f..63b31afacf84 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3914,6 +3914,9 @@ static struct sk_buff *validate_xmit_skb(struct sk_buff *skb, struct net_device
 
 	skb = validate_xmit_xfrm(skb, features, again);
 
+	if (!skb_frags_readable(skb))
+		goto out_kfree_skb;
+
 	return skb;
 
 out_kfree_skb:

base-commit: 3c6a041b317a9bb0c707343c0b99d2a29d523390
-- 
2.48.1.711.g2feabab25a-goog

Re: [PATCH net v1] netmem: prevent TX of unreadable skbs

[Jakub Kicinski]

On Tue,  4 Mar 2025 23:49:24 +0000 Mina Almasry wrote:
> @@ -3914,6 +3914,9 @@ static struct sk_buff *validate_xmit_skb(struct sk_buff *skb, struct net_device
>  
>  	skb = validate_xmit_xfrm(skb, features, again);
>  
> +	if (!skb_frags_readable(skb))
> +		goto out_kfree_skb;

I'd put this new check at the beginning rather than the end.
Feeding unreadable packets into GSO will not result in
much happiness.