# CVE-2021-47507: linux: In the Linux kernel, the following vulnerability has been resolved:  nfsd: Fix nsfd startup race (again)  Commit bd5a...

CVE-2021-47507 is fixed in linux on 1 platform, first by DEBIAN-CVE-2021-47507, released May 24, 2024. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2021-47507
- Priority: Routine
- CVSS: 4.7 (medium)
- EPSS: 0.0019
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: May 24, 2024

## 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

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 12.15 (bookworm) | 5.15.15-1 | [DEBIAN-CVE-2021-47507](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47507.md) | May 24, 2024 |
| Linux | linux Debian 13.5 (trixie) | 5.15.15-1 | [DEBIAN-CVE-2021-47507](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47507.md) | May 24, 2024 |
| Linux | linux Debian 14 | 5.15.15-1 | [DEBIAN-CVE-2021-47507](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47507.md) | May 24, 2024 |

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