CVE-2021-47371

What it is

In the Linux kernel, the following vulnerability has been resolved: nexthop: Fix memory leaks in nexthop notification chain listeners syzkaller discovered memory leaks [1] that can be reduced to the following commands: # ip nexthop add id 1 blackhole # devlink dev reload pci/0000:06:00.0 As part of the reload flow, mlxsw will unregister its netdevs and then unregister from the nexthop notification chain. Before unregistering from the notification chain, mlxsw will receive delete notifications for nexthop objects using netdevs registered by mlxsw or their uppers. mlxsw will not receive notifications for nexthops using netdevs that are not dismantled as part of the reload flow. For example, the blackhole nexthop above that internally uses the loopback netdev as its nexthop device. One way to fix this problem is to have listeners flush their nexthop tables after unregistering from the notification chain. This is error-prone as evident by this patch and also not symmetric with the registration path where a listener receives a dump of all the existing nexthops. Therefore, fix this problem by replaying delete notifications for the listener being unregistered. This is symmetric to the registration path and also consistent with the netdev notification chain. The above means that unregister_nexthop_notifier(), like register_nexthop_notifier(), will have to take RTNL in order to iterate over the existing nexthops and that any callers of the function cannot hold RTNL. This is true for mlxsw and netdevsim, but not for the VXLAN driver. To avoid a deadlock, change the latter to unregister its nexthop listener without holding RTNL, making it symmetric to the registration path. [1] unreferenced object 0xffff88806173d600 (size 512): comm "syz-executor.0", pid 1290, jiffies 4295583142 (age 143.507s) hex dump (first 32 bytes): 41 9d 1e 60 80 88 ff ff 08 d6 73 61 80 88 ff ff A..`......sa.... 08 d6 73 61 80 88 ff ff 01 00 00 00 00 00 00 00 ..sa............ backtrace: [<ffffffff81a6b576>] kmemleak_alloc_recursive include/linux/kmemleak.h:43 [inline] [<ffffffff81a6b576>] slab_post_alloc_hook+0x96/0x490 mm/slab.h:522 [<ffffffff81a716d3>] slab_alloc_node mm/slub.c:3206 [inline] [<ffffffff81a716d3>] slab_alloc mm/slub.c:3214 [inline] [<ffffffff81a716d3>] kmem_cache_alloc_trace+0x163/0x370 mm/slub.c:3231 [<ffffffff82e8681a>] kmalloc include/linux/slab.h:591 [inline] [<ffffffff82e8681a>] kzalloc include/linux/slab.h:721 [inline] [<ffffffff82e8681a>] mlxsw_sp_nexthop_obj_group_create drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c:4918 [inline] [<ffffffff82e8681a>] mlxsw_sp_nexthop_obj_new drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c:5054 [inline] [<ffffffff82e8681a>] mlxsw_sp_nexthop_obj_event+0x59a/0x2910 drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c:5239 [<ffffffff813ef67d>] notifier_call_chain+0xbd/0x210 kernel/notifier.c:83 [<ffffffff813f0662>] blocking_notifier_call_chain kernel/notifier.c:318 [inline] [<ffffffff813f0662>] blocking_notifier_call_chain+0x72/0xa0 kernel/notifier.c:306 [<ffffffff8384b9c6>] call_nexthop_notifiers+0x156/0x310 net/ipv4/nexthop.c:244 [<ffffffff83852bd8>] insert_nexthop net/ipv4/nexthop.c:2336 [inline] [<ffffffff83852bd8>] nexthop_add net/ipv4/nexthop.c:2644 [inline] [<ffffffff83852bd8>] rtm_new_nexthop+0x14e8/0x4d10 net/ipv4/nexthop.c:2913 [<ffffffff833e9a78>] rtnetlink_rcv_msg+0x448/0xbf0 net/core/rtnetlink.c:5572 [<ffffffff83608703>] netlink_rcv_skb+0x173/0x480 net/netlink/af_netlink.c:2504 [<ffffffff833de032>] rtnetlink_rcv+0x22/0x30 net/core/rtnetlink.c:5590 [<ffffffff836069de>] netlink_unicast_kernel net/netlink/af_netlink.c:1314 [inline] [<ffffffff836069de>] netlink_unicast+0x5ae/0x7f0 net/netlink/af_netlink.c:1340 [<ffffffff83607501>] netlink_sendmsg+0x8e1/0xe30 net/netlink/af_netlink.c:1929 [<ffffffff832fde84>] sock_sendmsg_nosec net/socket.c:704 [inline ---truncated---

At a glance

Exploitability

Can be exploited locally on the machine with a low-privilege account. High risk of data tampering, service disruption.

Exploit odds

0.2% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2024-05-21 15:15 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-06-17 04:17 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 0.2% in the next 30 days (EPSS).
• Severity: 7.1 HIGH (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2024-05-21 15:15 UTC

Last modified

2026-06-17 04:17 UTC

Exploit probability

0.2% · EPSS, next 30 days

Weakness

CWE-400 · Uncontrolled resource consumption

Record status

Analyzed

Affected

• Linux Kernel < 5.14.9
• Linux Kernel 5.15

Attack profile CVSS 3.1 · 7.1

Attack vector

Local

Complexity

Low

Privileges needed

Low

User interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

High

Availability

High

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2021-47371.md and follow it. Check whether this project is affected by CVE-2021-47371. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

Copy as ticket · More options · Status badge