Re: [PATCH v1 net 1/3] gtp: Use for_each_netdev_rcu() in gtp_genl_dump_pdp().

From: Simon Horman <horms@kernel.org>
Date: Wed, 8 Jan 2025 10:40:40 +0000

On Wed, Jan 08, 2025 at 03:28:32PM +0900, Kuniyuki Iwashima wrote:

quoted

gtp_newlink() links the gtp device to a list in dev_net(dev).

However, even after the gtp device is moved to another netns,
it stays on the list but should be invisible.

Let's use for_each_netdev_rcu() for netdev traversal in
gtp_genl_dump_pdp().

Note that gtp_dev_list is no longer used under RCU, so list
helpers are converted to the non-RCU variant.

Fixes: 459aa660eb1d ("gtp: add initial driver for datapath of GPRS Tunneling Protocol (GTP-U)")
Reported-by: Xiao Liang <redacted>
Closes: https://lore.kernel.org/netdev/CABAhCOQdBL6h9M2C+kd+bGivRJ9Q72JUxW+-gur0nub_=PmFPA@mail.gmail.com/ (local)
Signed-off-by: Kuniyuki Iwashima <redacted>
---
Cc: Pablo Neira Ayuso <pablo@netfilter.org>
Cc: Harald Welte <laforge@gnumonks.org>

...

quoted

@@ -2280,7 +2281,10 @@ static int gtp_genl_dump_pdp(struct sk_buff *skb,
 		return 0;
 
 	rcu_read_lock();
-	list_for_each_entry_rcu(gtp, &gn->gtp_dev_list, list) {
+	for_each_netdev_rcu(net, dev) {
+		if (dev->rtnl_link_ops != &gtp_link_ops)
+			continue;
+
 		if (last_gtp && last_gtp != gtp)
 			continue;
 		else

Hi Iwashima-san,

With this change gtp seems to be uninitialised here.
And, also, it looks like gn is now set but otherwise unused in this function.

Flagged by W=1 builds with clang-19.

Ah, thank you for catching these !

I'll squash this to v2.

---8<---

diff --git a/drivers/net/gtp.c b/drivers/net/gtp.c
index b905b7bc46cb..0d03e150efc6 100644
--- a/drivers/net/gtp.c
+++ b/drivers/net/gtp.c

@@ -2298,9 +2298,6 @@ static int gtp_genl_dump_pdp(struct sk_buff *skb,
 	struct net *net = sock_net(skb->sk);
 	struct net_device *dev;
 	struct pdp_ctx *pctx;
-	struct gtp_net *gn;
-
-	gn = net_generic(net, gtp_net_id);
 
 	if (cb->args[4])
 		return 0;

@@ -2310,6 +2307,8 @@ static int gtp_genl_dump_pdp(struct sk_buff *skb,
 		if (dev->rtnl_link_ops != &gtp_link_ops)
 			continue;
 
+		gtp = netdev_priv(dev);
+
 		if (last_gtp && last_gtp != gtp)
 			continue;
 		else
---8<---