CVE-2026-45895 (GCVE-0-2026-45895)

Vulnerability from cvelistv5 – Published: 2026-05-27 12:17 – Updated: 2026-05-27 12:17
VLAI
Title
quota: fix livelock between quotactl and freeze_super
Summary
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.
Severity
5.5 (Medium)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: 576215cffdefc1f0ceebffd87abb390926e6b037 , < 37ccd48cf35f3c8b9f2ea961a7b486b91eb71a82 (git)
Affected: 576215cffdefc1f0ceebffd87abb390926e6b037 , < 414259caf81a397563fc9baca9c0ef856c4a97cf (git)
Affected: 576215cffdefc1f0ceebffd87abb390926e6b037 , < 02bb1500f1479750e6557c8044f6a2d7e9d30c12 (git)
Affected: 576215cffdefc1f0ceebffd87abb390926e6b037 , < 53b2314b26b6640a3657cc924de63a1a8f26ac4d (git)
Affected: 576215cffdefc1f0ceebffd87abb390926e6b037 , < 77449e453dfc006ad738dec55374c4cbc056fd39 (git)
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Linux Linux Affected: 6.5
Unaffected: 0 , < 6.5 (semver)
Unaffected: 6.6.128 , ≤ 6.6.* (semver)
Unaffected: 6.12.75 , ≤ 6.12.* (semver)
Unaffected: 6.18.14 , ≤ 6.18.* (semver)
Unaffected: 6.19.4 , ≤ 6.19.* (semver)
Unaffected: 7.0 , ≤ * (original_commit_for_fix)
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nquota: fix livelock between quotactl and freeze_super\n\nWhen a filesystem is frozen, quotactl_block() enters a retry loop\nwaiting for the filesystem to thaw. It acquires s_umount, checks the\nfreeze state, drops s_umount and uses sb_start_write() - sb_end_write()\npair to wait for the unfreeze.\n\nHowever, this retry loop can trigger a livelock issue, specifically on\nkernels with preemption disabled.\n\nThe mechanism is as follows:\n1. freeze_super() sets SB_FREEZE_WRITE and calls sb_wait_write().\n2. sb_wait_write() calls percpu_down_write(), which initiates\n   synchronize_rcu().\n3. Simultaneously, quotactl_block() spins in its retry loop, immediately\n   executing the sb_start_write() - sb_end_write() pair.\n4. Because the kernel is non-preemptible and the loop contains no\n   scheduling points, quotactl_block() never yields the CPU. This\n   prevents that CPU from reaching an RCU quiescent state.\n5. synchronize_rcu() in the freezer thread waits indefinitely for the\n   quotactl_block() CPU to report a quiescent state.\n6. quotactl_block() spins indefinitely waiting for the freezer to\n   advance, which it cannot do as it is blocked on the RCU sync.\n\nThis results in a hang of the freezer process and 100% CPU usage by the\nquota process.\n\nWhile this can occur intermittently on multi-core systems, it is\nreliably reproducing on a node with the following script, running both\nthe freezer and the quota toggle on the same CPU:\n\n  # mkfs.ext4 -O quota /dev/sda 2g \u0026\u0026 mkdir a_mount\n  # mount /dev/sda -o quota,usrquota,grpquota a_mount\n  # taskset -c 3 bash -c \"while true; do xfs_freeze -f a_mount; \\\n    xfs_freeze -u a_mount; done\" \u0026\n  # taskset -c 3 bash -c \"while true; do quotaon a_mount; \\\n    quotaoff a_mount; done\" \u0026\n\nAdding cond_resched() to the retry loop fixes the issue. It acts as an\nRCU quiescent state, allowing synchronize_rcu() in percpu_down_write()\nto complete."
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Simultaneously, quotactl_block() spins in its retry loop, immediately\\n   executing the sb_start_write() - sb_end_write() pair.\\n4. Because the kernel is non-preemptible and the loop contains no\\n   scheduling points, quotactl_block() never yields the CPU. This\\n   prevents that CPU from reaching an RCU quiescent state.\\n5. synchronize_rcu() in the freezer thread waits indefinitely for the\\n   quotactl_block() CPU to report a quiescent state.\\n6. quotactl_block() spins indefinitely waiting for the freezer to\\n   advance, which it cannot do as it is blocked on the RCU sync.\\n\\nThis results in a hang of the freezer process and 100% CPU usage by the\\nquota process.\\n\\nWhile this can occur intermittently on multi-core systems, it is\\nreliably reproducing on a node with the following script, running both\\nthe freezer and the quota toggle on the same CPU:\\n\\n  # mkfs.ext4 -O quota /dev/sda 2g \u0026\u0026 mkdir a_mount\\n  # mount /dev/sda -o quota,usrquota,grpquota a_mount\\n  # taskset -c 3 bash -c \\\"while true; do xfs_freeze -f a_mount; \\\\\\n    xfs_freeze -u a_mount; done\\\" \u0026\\n  # taskset -c 3 bash -c \\\"while true; do quotaon a_mount; \\\\\\n    quotaoff a_mount; done\\\" \u0026\\n\\nAdding cond_resched() to the retry loop fixes the issue. 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    "redhat_vex": {
      "aggregate_severity": "Low",
      "current_release_date": "2026-06-27T16:19:44+00:00",
      "cve": "CVE-2026-45895",
      "id": "CVE-2026-45895",
      "initial_release_date": "2026-05-27T00:00:00+00:00",
      "product_status:known_affected": "90",
      "product_status:known_not_affected": "184",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: quota: fix livelock between quotactl and freeze_super",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-45895.json",
      "version": "3"
    }
  }
}



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Sightings

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Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
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  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
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  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.