CVE-2023-54276

Description

In the Linux kernel, the following vulnerability has been resolved: nfsd: move init of percpu reply_cache_stats counters back to nfsd_init_net Commit f5f9d4a314da ("nfsd: move reply cache initialization into nfsd startup") moved the initialization of the reply cache into nfsd startup, but didn't account for the stats counters, which can be accessed before nfsd is ever started. The result can be a NULL pointer dereference when someone accesses /proc/fs/nfsd/reply_cache_stats while nfsd is still shut down. This is a regression and a user-triggerable oops in the right situation: - non-x86_64 arch - /proc/fs/nfsd is mounted in the namespace - nfsd is not started in the namespace - unprivileged user calls "cat /proc/fs/nfsd/reply_cache_stats" Although this is easy to trigger on some arches (like aarch64), on x86_64, calling this_cpu_ptr(NULL) evidently returns a pointer to the fixed_percpu_data. That struct looks just enough like a newly initialized percpu var to allow nfsd_reply_cache_stats_show to access it without Oopsing. Move the initialization of the per-net+per-cpu reply-cache counters back into nfsd_init_net, while leaving the rest of the reply cache allocations to be done at nfsd startup time. Kudos to Eirik who did most of the legwork to track this down.

Gravité et risque d'exploitation

CVE-2023-54276 obtient un score CVSS de 0.0/10, soit une gravité non évaluée. Selon le modèle EPSS, la probabilité qu'elle soit exploitée dans les 30 prochains jours est de 0.20 %, ce qui la place devant 9.2 % des CVE référencées.

Que faire ?

• Vérifiez si Linux (versions 6.4.4, f5f9d4a314da88c0a5faa6d168bf69081b7a25ae, e7e571ed4ec7bb50136233d8e7b986efef2af8c1, <=*, <3025d489f9c8984d1bf5916c4a20097ed80fca5c, <6.3, 6.5, 0, <8549384d0f65981761fe2077d04fa2a8d37b54e0, 70fdee548c036c6bdb496f284c9e78f1654b6dd0, <768c408594b52d8531e1a8ab62e5620c19213e73, <66a178177b2b3bb1d71e854c5e7bbb320eb0e566, 4e18b58b106e34ac69d3052dd91f520bd83cf2fc, <=6.4.*, 6.3, <ed9ab7346e908496816cffdecd46932035f66e2e) est présent sur votre parc.
• Appliquez le correctif ou la version corrigée indiqués dans les références de l'éditeur.
• À défaut de correctif, limitez l'exposition (filtrage réseau, désactivation du composant).
• Automatisez la détection : les agents CVE Heimdall (gratuits, open source) corrèlent l'inventaire de vos serveurs avec la base CVE.

Références

• https://git.kernel.org/stable/c/3025d489f9c8984d1bf5916c4a20097ed80fca5c
• https://git.kernel.org/stable/c/8549384d0f65981761fe2077d04fa2a8d37b54e0
• https://git.kernel.org/stable/c/66a178177b2b3bb1d71e854c5e7bbb320eb0e566
• https://git.kernel.org/stable/c/768c408594b52d8531e1a8ab62e5620c19213e73
• https://git.kernel.org/stable/c/ed9ab7346e908496816cffdecd46932035f66e2e