FKIE_CVE-2026-45895
Vulnerability from fkie_nvd - Published: 2026-05-27 14:17 - Updated: 2026-06-25 21:09
Severity
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.
References
Impacted products
| Vendor | Product | Version | |
|---|---|---|---|
| linux | linux_kernel | * | |
| linux | linux_kernel | * | |
| linux | linux_kernel | * | |
| linux | linux_kernel | * |
{
"affected": [
{
"affectedData": [
{
"defaultStatus": "unaffected",
"product": "Linux",
"programFiles": [
"fs/quota/quota.c"
],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"versions": [
{
"lessThan": "37ccd48cf35f3c8b9f2ea961a7b486b91eb71a82",
"status": "affected",
"version": "576215cffdefc1f0ceebffd87abb390926e6b037",
"versionType": "git"
},
{
"lessThan": "414259caf81a397563fc9baca9c0ef856c4a97cf",
"status": "affected",
"version": "576215cffdefc1f0ceebffd87abb390926e6b037",
"versionType": "git"
},
{
"lessThan": "02bb1500f1479750e6557c8044f6a2d7e9d30c12",
"status": "affected",
"version": "576215cffdefc1f0ceebffd87abb390926e6b037",
"versionType": "git"
},
{
"lessThan": "53b2314b26b6640a3657cc924de63a1a8f26ac4d",
"status": "affected",
"version": "576215cffdefc1f0ceebffd87abb390926e6b037",
"versionType": "git"
},
{
"lessThan": "77449e453dfc006ad738dec55374c4cbc056fd39",
"status": "affected",
"version": "576215cffdefc1f0ceebffd87abb390926e6b037",
"versionType": "git"
}
]
},
{
"defaultStatus": "affected",
"product": "Linux",
"programFiles": [
"fs/quota/quota.c"
],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"versions": [
{
"status": "affected",
"version": "6.5"
},
{
"lessThan": "6.5",
"status": "unaffected",
"version": "0",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.6.*",
"status": "unaffected",
"version": "6.6.128",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.12.*",
"status": "unaffected",
"version": "6.12.75",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.18.*",
"status": "unaffected",
"version": "6.18.14",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.19.*",
"status": "unaffected",
"version": "6.19.4",
"versionType": "semver"
},
{
"lessThanOrEqual": "*",
"status": "unaffected",
"version": "7.0",
"versionType": "original_commit_for_fix"
}
]
}
],
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}
],
"configurations": [
{
"nodes": [
{
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"matchCriteriaId": "A502C6C1-0CFB-4C9B-8A24-C76507206FA7",
"versionEndExcluding": "6.6.128",
"versionStartIncluding": "6.5",
"vulnerable": true
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"matchCriteriaId": "BCE16369-98ED-41CF-8995-DFDC10B288D2",
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"versionStartIncluding": "6.7",
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"negate": false,
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],
"cveTags": [],
"descriptions": [
{
"lang": "en",
"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."
}
],
"id": "CVE-2026-45895",
"lastModified": "2026-06-25T21:09:58.390",
"metrics": {
"cvssMetricV31": [
{
"cvssData": {
"attackComplexity": "LOW",
"attackVector": "LOCAL",
"availabilityImpact": "HIGH",
"baseScore": 5.5,
"baseSeverity": "MEDIUM",
"confidentialityImpact": "NONE",
"integrityImpact": "NONE",
"privilegesRequired": "LOW",
"scope": "UNCHANGED",
"userInteraction": "NONE",
"vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
"version": "3.1"
},
"exploitabilityScore": 1.8,
"impactScore": 3.6,
"source": "nvd@nist.gov",
"type": "Primary"
}
]
},
"published": "2026-05-27T14:17:03.733",
"references": [
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"tags": [
"Patch"
],
"url": "https://git.kernel.org/stable/c/02bb1500f1479750e6557c8044f6a2d7e9d30c12"
},
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"tags": [
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"url": "https://git.kernel.org/stable/c/37ccd48cf35f3c8b9f2ea961a7b486b91eb71a82"
},
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"tags": [
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"url": "https://git.kernel.org/stable/c/414259caf81a397563fc9baca9c0ef856c4a97cf"
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{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"tags": [
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"url": "https://git.kernel.org/stable/c/53b2314b26b6640a3657cc924de63a1a8f26ac4d"
},
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"tags": [
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],
"url": "https://git.kernel.org/stable/c/77449e453dfc006ad738dec55374c4cbc056fd39"
}
],
"sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"vulnStatus": "Analyzed",
"weaknesses": [
{
"description": [
{
"lang": "en",
"value": "NVD-CWE-noinfo"
}
],
"source": "nvd@nist.gov",
"type": "Primary"
}
]
}
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Browse all ATT&CK techniques and the vulnerabilities related to each.
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