CVE-2026-45895

Description

In the Linux kernel, the following vulnerability has been resolved: quota: fix livelock between quotactl and freeze_super When a filesystem is frozen, quotactl_block() enters a retry loop waiting for the filesystem to thaw. It acquires s_umount, checks the freeze state, drops s_umount and uses sb_start_write() - sb_end_write() pair to wait for the unfreeze. However, this retry loop can trigger a livelock issue, specifically on kernels with preemption disabled. The mechanism is as follows: 1. freeze_super() sets SB_FREEZE_WRITE and calls sb_wait_write(). 2. sb_wait_write() calls percpu_down_write(), which initiates synchronize_rcu(). 3. Simultaneously, quotactl_block() spins in its retry loop, immediately executing the sb_start_write() - sb_end_write() pair. 4. Because the kernel is non-preemptible and the loop contains no scheduling points, quotactl_block() never yields the CPU. This prevents that CPU from reaching an RCU quiescent state. 5. synchronize_rcu() in the freezer thread waits indefinitely for the quotactl_block() CPU to report a quiescent state. 6. quotactl_block() spins indefinitely waiting for the freezer to advance, which it cannot do as it is blocked on the RCU sync. This results in a hang of the freezer process and 100% CPU usage by the quota process. While this can occur intermittently on multi-core systems, it is reliably reproducing on a node with the following script, running both the freezer and the quota toggle on the same CPU: # mkfs.ext4 -O quota /dev/sda 2g && mkdir a_mount # mount /dev/sda -o quota,usrquota,grpquota a_mount # taskset -c 3 bash -c "while true; do xfs_freeze -f a_mount; \ xfs_freeze -u a_mount; done" & # taskset -c 3 bash -c "while true; do quotaon a_mount; \ quotaoff a_mount; done" & Adding cond_resched() to the retry loop fixes the issue. It acts as an RCU quiescent state, allowing synchronize_rcu() in percpu_down_write() to complete.

Gravité et risque d'exploitation

CVE-2026-45895 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 0.16 %, ce qui la place devant 5.0 % des CVE référencées.

Que faire ?

• Vérifiez si Linux (versions <414259caf81a397563fc9baca9c0ef856c4a97cf, <53b2314b26b6640a3657cc924de63a1a8f26ac4d, <=6.12.*, <6.5, 0, 7.0, <77449e453dfc006ad738dec55374c4cbc056fd39, 6.12.75, 576215cffdefc1f0ceebffd87abb390926e6b037, 6.5, <=6.6.*, <=6.19.*, <37ccd48cf35f3c8b9f2ea961a7b486b91eb71a82, <=6.18.*, 6.6.128, 6.19.4, <=*, <02bb1500f1479750e6557c8044f6a2d7e9d30c12, 6.18.14) 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/37ccd48cf35f3c8b9f2ea961a7b486b91eb71a82
• https://git.kernel.org/stable/c/414259caf81a397563fc9baca9c0ef856c4a97cf
• https://git.kernel.org/stable/c/02bb1500f1479750e6557c8044f6a2d7e9d30c12
• https://git.kernel.org/stable/c/53b2314b26b6640a3657cc924de63a1a8f26ac4d
• https://git.kernel.org/stable/c/77449e453dfc006ad738dec55374c4cbc056fd39