Commit debac3a20dec for kernel
commit debac3a20dec524a59625cf10fa2f18571127824
Author: Kuniyuki Iwashima <kuniyu@google.com>
Date: Tue Sep 1 00:55:44 2026 +0000
net: Remove conflicting altnames for dying netns in __dev_change_net_namespace().
syzbot reported the warning in cfg80211_pernet_exit(). [0]
The repro does the following:
1. create two device in root netns and non-root netns
2. assign the same altname for the two devices
3. remove the non-root netns
Since commit 7663d522099e ("net: check for altname conflicts
when changing netdev's netns"), cfg80211_switch_netns() and
cfg802154_switch_netns() fail if init_net has a device with the
conflicting altname.
default_device_exit_net() had the same issue and commit d09486a04f5d
("net: fix removing a namespace with conflicting altnames") fixed it.
cfg80211_pernet_exit() and cfg802154_pernet_exit() need the same fix.
Let's generalise the fix by removing conflicting altnames for dying
netns in __dev_change_net_namespace().
[0]:
cfg80211_switch_netns(rdev, &init_net)
WARNING: net/wireless/core.c:1871 at cfg80211_pernet_exit+0xd5/0x120 net/wireless/core.c:1871, CPU#1: kworker/u8:9/1160
Modules linked in:
CPU: 1 UID: 0 PID: 1160 Comm: kworker/u8:9 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Workqueue: netns cleanup_net
RIP: 0010:cfg80211_pernet_exit+0xd5/0x120 net/wireless/core.c:1871
Code: e8 03 42 80 3c 20 00 74 08 4c 89 f7 e8 b4 ef 0e f7 4d 8b 36 49 81 fe 20 10 4a 90 74 12 e8 03 3d 9f f6 eb 85 e8 fc 3c 9f f6 90 <0f> 0b 90 eb cc e8 f1 3c 9f f6 eb 05 e8 ea 3c 9f f6 5b 41 5c 41 5e
RSP: 0018:ffffc900057a78f0 EFLAGS: 00010293
RAX: ffffffff8b287154 RBX: ffff88807ba72780 RCX: ffff8880213e8000
RDX: 0000000000000000 RSI: 00000000ffffffef RDI: 0000000000000000
RBP: 00000000ffffffef R08: ffffffff9024cc67 R09: 0000000000000000
R10: fffff52000af4eb0 R11: fffffbfff204998d R12: dffffc0000000000
R13: ffffffff904a1080 R14: ffff888144ed0008 R15: ffff888144ed0e20
FS: 0000000000000000(0000) GS:ffff888124de6000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00005642de0a8a70 CR3: 000000007a40c000 CR4: 00000000003526f0
Call Trace:
<TASK>
ops_exit_list net/core/net_namespace.c:200 [inline]
ops_undo_list+0x43d/0x8d0 net/core/net_namespace.c:253
cleanup_net+0x572/0x810 net/core/net_namespace.c:706
process_one_work kernel/workqueue.c:3387 [inline]
process_scheduled_works+0xc3d/0x1630 kernel/workqueue.c:3470
worker_thread+0xa47/0xfb0 kernel/workqueue.c:3551
kthread+0x38b/0x480 kernel/kthread.c:436
ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>
Fixes: 36fbf1e52bd3 ("net: rtnetlink: add linkprop commands to add and delete alternative ifnames")
Reported-by: syzbot+74f338e09f1ef3ee6457@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/6a96219e.04428c52.29b18.0001.GAE@google.com/T/
Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20260901005550.2042357-1-kuniyu@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
diff --git a/net/core/dev.c b/net/core/dev.c
index 38336858c168..290e0f099e6b 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -12703,7 +12703,7 @@ int __dev_change_net_namespace(struct net_device *dev, struct net *net,
const char *pat, int new_ifindex,
struct netlink_ext_ack *extack)
{
- struct netdev_name_node *name_node;
+ struct netdev_name_node *name_node, *tmp;
struct net *net_old = dev_net(dev);
char new_name[IFNAMSIZ] = {};
int err, new_nsid;
@@ -12749,13 +12749,19 @@ int __dev_change_net_namespace(struct net_device *dev, struct net *net,
}
/* Check that none of the altnames conflicts. */
err = -EEXIST;
- netdev_for_each_altname(dev, name_node) {
- if (netdev_name_in_use(net, name_node->name)) {
- NL_SET_ERR_MSG_FMT(extack,
- "An interface with the altname %s exists in the target netns",
- name_node->name);
- goto out;
+ netdev_for_each_altname_safe(dev, name_node, tmp) {
+ if (!netdev_name_in_use(net, name_node->name))
+ continue;
+
+ if (!check_net(net_old)) {
+ __netdev_name_node_alt_destroy(name_node);
+ continue;
}
+
+ NL_SET_ERR_MSG_FMT(extack,
+ "An interface with the altname %s exists in the target netns",
+ name_node->name);
+ goto out;
}
/* Check that new_ifindex isn't used yet. */
@@ -13210,7 +13216,6 @@ static struct pernet_operations __net_initdata netdev_net_ops = {
static void __net_exit default_device_exit_net(struct net *net)
{
- struct netdev_name_node *name_node, *tmp;
struct net_device *dev, *aux;
/*
* Push all migratable network devices back to the
@@ -13234,10 +13239,6 @@ static void __net_exit default_device_exit_net(struct net *net)
if (netdev_name_in_use(&init_net, fb_name))
snprintf(fb_name, IFNAMSIZ, "dev%%d");
- netdev_for_each_altname_safe(dev, name_node, tmp)
- if (netdev_name_in_use(&init_net, name_node->name))
- __netdev_name_node_alt_destroy(name_node);
-
err = dev_change_net_namespace(dev, &init_net, fb_name);
if (err) {
pr_emerg("%s: failed to move %s to init_net: %d\n",