CVE-2021-47507: nfsd: Fix nsfd startup race (again)

Severity: medium (CVSS 4.7 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2024-05-24 · updated 2026-06-17
Weakness: CWE-362

Description

In the Linux kernel, the following vulnerability has been resolved: nfsd: Fix nsfd startup race (again) Commit bd5ae9288d64 ("nfsd: register pernet ops last, unregister first") has re-opened rpc_pipefs_event() race against nfsd_net_id registration (register_pernet_subsys()) which has been fixed by commit bb7ffbf29e76 ("nfsd: fix nsfd startup race triggering BUG_ON"). Restore the order of register_pernet_subsys() vs register_cld_notifier(). Add WARN_ON() to prevent a future regression. Crash info: Unable to handle kernel NULL pointer dereference at virtual address 0000000000000012 CPU: 8 PID: 345 Comm: mount Not tainted 5.4.144-... #1 pc : rpc_pipefs_event+0x54/0x120 [nfsd] lr : rpc_pipefs_event+0x48/0x120 [nfsd] Call trace: rpc_pipefs_event+0x54/0x120 [nfsd] blocking_notifier_call_chain rpc_fill_super get_tree_keyed rpc_fs_get_tree vfs_get_tree do_mount ksys_mount __arm64_sys_mount el0_svc_handler el0_svc

Affected products

Linux kernel: from 5.4.102 before 5.4.165; from 5.10.20 before 5.10.85; from 5.11.3 before 5.15.8; 5.16-rc1, 5.16-rc2, 5.16-rc3, 5.16-rc4 — fixed in 5.10.85, 5.15.8, 5.4.165

How to fix

Upgrade to a fixed version: Linux kernel 5.10.85, 5.15.8, 5.4.165. Check the vendor advisory for mitigations.

References

Get alerted when CVE-2021-47507 or the next vulnerability affects your stack