Linux Kernel up to 5.14.8 nexthop unregister_nexthop_notifier memory leak

Summaryinfo

A vulnerability described as critical has been identified in Linux Kernel up to 5.14.8. This affects the function unregister_nexthop_notifier of the component nexthop. Executing a manipulation can lead to memory leak. This vulnerability appears as CVE-2021-47371. The attacker needs to be present on the local network. There is no available exploit. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability classified as critical was found in Linux Kernel up to 5.14.8. This vulnerability affects the function unregister_nexthop_notifier of the component nexthop. The manipulation with an unknown input leads to a memory leak vulnerability. The CWE definition for the vulnerability is CWE-401. The product does not sufficiently track and release allocated memory after it has been used, which slowly consumes remaining memory. As an impact it is known to affect availability. CVE summarizes:

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: [] kmemleak_alloc_recursive include/linux/kmemleak.h:43 [inline] [] slab_post_alloc_hook+0x96/0x490 mm/slab.h:522 [] slab_alloc_node mm/slub.c:3206 [inline] [] slab_alloc mm/slub.c:3214 [inline] [] kmem_cache_alloc_trace+0x163/0x370 mm/slub.c:3231 [] kmalloc include/linux/slab.h:591 [inline] [] kzalloc include/linux/slab.h:721 [inline] [] mlxsw_sp_nexthop_obj_group_create drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c:4918 [inline] [] mlxsw_sp_nexthop_obj_new drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c:5054 [inline] [] mlxsw_sp_nexthop_obj_event+0x59a/0x2910 drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c:5239 [] notifier_call_chain+0xbd/0x210 kernel/notifier.c:83 [] blocking_notifier_call_chain kernel/notifier.c:318 [inline] [] blocking_notifier_call_chain+0x72/0xa0 kernel/notifier.c:306 [] call_nexthop_notifiers+0x156/0x310 net/ipv4/nexthop.c:244 [] insert_nexthop net/ipv4/nexthop.c:2336 [inline] [] nexthop_add net/ipv4/nexthop.c:2644 [inline] [] rtm_new_nexthop+0x14e8/0x4d10 net/ipv4/nexthop.c:2913 [] rtnetlink_rcv_msg+0x448/0xbf0 net/core/rtnetlink.c:5572 [] netlink_rcv_skb+0x173/0x480 net/netlink/af_netlink.c:2504 [] rtnetlink_rcv+0x22/0x30 net/core/rtnetlink.c:5590 [] netlink_unicast_kernel net/netlink/af_netlink.c:1314 [inline] [] netlink_unicast+0x5ae/0x7f0 net/netlink/af_netlink.c:1340 [] netlink_sendmsg+0x8e1/0xe30 net/netlink/af_netlink.c:1929 [] sock_sendmsg_nosec net/socket.c:704 [inline ---truncated---

The advisory is available at git.kernel.org. This vulnerability was named CVE-2021-47371. The exploitation appears to be difficult. Access to the local network is required for this attack. Technical details are known, but there is no available exploit.

Upgrading to version 5.14.9 eliminates this vulnerability. Applying the patch 741760fa6252/3106a0847525 is able to eliminate this problem. The bugfix is ready for download at git.kernel.org. The best possible mitigation is suggested to be upgrading to the latest version.

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Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 5.14.0
• 5.14.1
• 5.14.2
• 5.14.3
• 5.14.4
• 5.14.5
• 5.14.6
• 5.14.7
• 5.14.8

License

• open-source

Website

• Vendor: https://www.kernel.org/

CPE 2.3info

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CPE 2.2info

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