memory leak in ndisc_send

Based on kernel commit 9d66f26fefac:

Bug Analysis and Technical Breakdown

Root Cause

The memory leak is caused by improper lifecycle management of buffered transmit packets (sk_buff) in the Option HSO USB network driver (drivers/net/usb/hso.c).

Specifically:

When a network packet is transmitted via hso_net_start_xmit() (drivers/net/usb/hso.c:766), the driver checks device activity via hso_get_activity(odev->parent).
hso_get_activity() returns -EAGAIN if the underlying USB device is not in USB_STATE_CONFIGURED (e.g., when the device is suspended, disconnected, or tearing down: udev->state = USB_STATE_NOTATTACHED).

On -EAGAIN, hso_net_start_xmit() buffers the packet in odev->skb_tx_buf and returns NETDEV_TX_OK:

if (hso_get_activity(odev->parent) == -EAGAIN) {
    odev->skb_tx_buf = skb;
    return NETDEV_TX_OK;
}

By returning NETDEV_TX_OK, the driver assumes sole ownership of skb. However, drivers/net/usb/hso.c fails to free odev->skb_tx_buf:
- Neither hso_net_close() nor hso_free_net_device() checks or calls dev_kfree_skb(odev->skb_tx_buf) before free_netdev(hso_net->net) frees struct hso_net.
- Additionally, hso_net_open() resets odev->skb_tx_buf = NULL without freeing any previous buffer.

Trigger Mechanism

In the reproducer, a virtual USB device handled by hso is attached and its network interface is registered. Duplicate Address Detection (DAD) for IPv6 triggers addrconf_dad_work() -> addrconf_dad_completed() -> ndisc_send_rs() to send an ICMPv6 Router Solicitation packet. When the USB device disconnects or shuts down while this frame is queued, hso_get_activity() returns -EAGAIN. The Router Solicitation skb is stored into odev->skb_tx_buf. During driver teardown (hso_disconnect() -> hso_free_interface() -> hso_free_net_device()), the skb and its allocated data head buffer (kmalloc_reserve) are never released, triggering kmemleak reports for both objects.

Affected Components

File: drivers/net/usb/hso.c
Functions: hso_net_start_xmit(), hso_net_close(), hso_free_net_device(), hso_net_open()
Structs & Fields: struct hso_net::skb_tx_buf

ID	Workflow	Result	Correct	Bug	Created	Started	Finished	Revision
68971053	assessment-security	DenialOfService: ✅ Exploitable: ❌ FilesystemTrigger: ❌ FuzzingArtifact: ❌ MemoryCorruption: ❌ NetworkNeedsSetup: ❌ NetworkTrigger: ❌ PeripheralTrigger: ✅ RemoteTrigger: ❌ Unprivileged: ❌ UserNamespace: ❌ VMGuestTrigger: ❌ VMHostTrigger: ❌	❓	memory leak in ndisc_send_rs (4)	2026/11/12 22:45	2026/11/12 22:45	2026/11/12 23:29	c0087d7f

assessment-security

DenialOfService: ✅ Exploitable: ❌ FilesystemTrigger: ❌ FuzzingArtifact: ❌ MemoryCorruption: ❌ NetworkNeedsSetup: ❌ NetworkTrigger: ❌ PeripheralTrigger: ✅ RemoteTrigger: ❌ Unprivileged: ❌ UserNamespace: ❌ VMGuestTrigger: ❌ VMHostTrigger: ❌

❓

memory leak in ndisc_send_rs (4)

2026/11/12 22:45

2026/11/12 23:29

c0087d7f

Kernel	Title	Rank 🛈	Repro	Count	Last	Reported	Patched	Status
upstream	memory leak in ndisc_send_rs net	3	syz, C	2	1854d	1901d	22/29	fixed on 2023/02/24 13:50
upstream	memory leak in ndisc_send_rs (2) net	3	syz, C	1	1349d	1349d	0/29	closed as invalid on 2023/04/12 12:24
upstream	memory leak in ndisc_send_rs (3) net	3	syz, C	1	1244d	1244d	0/29	closed as invalid on 2024/03/12 15:57

Rank 🛈

upstream

memory leak in ndisc_send_rs net

syz, C

1854d

1901d

22/29

fixed on 2023/02/24 13:50

upstream

memory leak in ndisc_send_rs (2) net

syz, C

1349d

0/29

closed as invalid on 2023/04/12 12:24

upstream

memory leak in ndisc_send_rs (3) net

syz, C

1244d

0/29

closed as invalid on 2024/03/12 15:57

BUG: memory leak unreferenced object 0xffff888100e9f200 (size 240): comm "kworker/u8:2", pid 5708, jiffies 4294993435 hex dump (first 32 bytes): 00 00 00 00 00 00 00 00 00 f2 e9 00 81 88 ff ff ................ 00 20 bd 23 81 88 ff ff 80 31 48 02 81 88 ff ff . .#.....1H..... backtrace (crc 28f53d77): kmemleak_alloc_recursive include/linux/kmemleak.h:44 [inline] slab_post_alloc_hook mm/slub.c:4733 [inline] slab_alloc_node mm/slub.c:5033 [inline] kmem_cache_alloc_node_noprof+0x368/0x400 mm/slub.c:5105 __alloc_skb+0xdc/0x4e0 net/core/skbuff.c:705 alloc_skb include/linux/skbuff.h:1390 [inline] ndisc_alloc_skb+0x46/0xf0 net/ipv6/ndisc.c:421 ndisc_send_rs+0x49/0x2f0 net/ipv6/ndisc.c:708 addrconf_dad_completed+0x1f9/0x6c0 net/ipv6/addrconf.c:4422 addrconf_dad_begin net/ipv6/addrconf.c:4184 [inline] addrconf_dad_work+0x5c8/0x910 net/ipv6/addrconf.c:4289 process_one_work+0x2b7/0x5c0 kernel/workqueue.c:3495 process_scheduled_works kernel/workqueue.c:3578 [inline] worker_thread+0x255/0x4a0 kernel/workqueue.c:3659 kthread+0x150/0x1a0 kernel/kthread.c:436 ret_from_fork+0x219/0x490 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 BUG: memory leak unreferenced object 0xffff888106538b00 (size 704): comm "kworker/u8:2", pid 5708, jiffies 4294993435 hex dump (first 32 bytes): 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 60 00 00 00 00 08 3a ff fe 80 00 00 00 00 00 00 `.....:......... backtrace (crc 261f6968): kmemleak_alloc_recursive include/linux/kmemleak.h:44 [inline] slab_post_alloc_hook mm/slub.c:4733 [inline] slab_alloc_node mm/slub.c:5033 [inline] kmem_cache_alloc_node_noprof+0x368/0x400 mm/slub.c:5105 kmalloc_reserve+0xd2/0x1b0 net/core/skbuff.c:616 __alloc_skb+0x15d/0x4e0 net/core/skbuff.c:716 alloc_skb include/linux/skbuff.h:1390 [inline] ndisc_alloc_skb+0x46/0xf0 net/ipv6/ndisc.c:421 ndisc_send_rs+0x49/0x2f0 net/ipv6/ndisc.c:708 addrconf_dad_completed+0x1f9/0x6c0 net/ipv6/addrconf.c:4422 addrconf_dad_begin net/ipv6/addrconf.c:4184 [inline] addrconf_dad_work+0x5c8/0x910 net/ipv6/addrconf.c:4289 process_one_work+0x2b7/0x5c0 kernel/workqueue.c:3495 process_scheduled_works kernel/workqueue.c:3578 [inline] worker_thread+0x255/0x4a0 kernel/workqueue.c:3659 kthread+0x150/0x1a0 kernel/kthread.c:436 ret_from_fork+0x219/0x490 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 connection error: failed to recv *flatrpc.ExecutorMessageRawT: EOF

Crashes (1):
Time	Kernel	Commit	Syzkaller	Config	Log	Report	Syz repro	C repro	VM info	Assets (help?)	Manager	Title
2026/11/12 17:51	upstream	9d66f26fefac	d6166547	.config	console log	report	syz / log			[disk image] [vmlinux] [kernel image]	ci-upstream-gce-leak	memory leak in ndisc_send_rs

Crashes (1):

Assets (help?)