{"id":"CVE-2026-45895","state":"PUBLISHED","title":"quota: fix livelock between quotactl and freeze_super","description":"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 && 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\" &\n  # taskset -c 3 bash -c \"while true; do quotaon a_mount; \\\n    quotaoff a_mount; done\" &\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.","publishedAt":"2026-05-27T12:17:05.666Z","updatedAt":"2026-05-27T12:17:05.666Z","severity":null,"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"576215cffdefc1f0ceebffd87abb390926e6b037","status":"affected","lessThan":"37ccd48cf35f3c8b9f2ea961a7b486b91eb71a82","versionType":"git"},{"version":"576215cffdefc1f0ceebffd87abb390926e6b037","status":"affected","lessThan":"414259caf81a397563fc9baca9c0ef856c4a97cf","versionType":"git"},{"version":"576215cffdefc1f0ceebffd87abb390926e6b037","status":"affected","lessThan":"02bb1500f1479750e6557c8044f6a2d7e9d30c12","versionType":"git"},{"version":"576215cffdefc1f0ceebffd87abb390926e6b037","status":"affected","lessThan":"53b2314b26b6640a3657cc924de63a1a8f26ac4d","versionType":"git"},{"version":"576215cffdefc1f0ceebffd87abb390926e6b037","status":"affected","lessThan":"77449e453dfc006ad738dec55374c4cbc056fd39","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/quota/quota.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.5","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.5","versionType":"semver"},{"version":"6.6.128","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.75","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.14","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"6.19.4","status":"unaffected","lessThanOrEqual":"6.19.*","versionType":"semver"},{"version":"7.0","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/quota/quota.c"]}],"references":["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"],"weaknesses":[],"ingestedAt":"2026-10-29T20:12:07.131Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/45xxx/CVE-2026-45895.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-45895","state":"PUBLISHED","datePublished":"2026-05-27T12:17:05.666Z","dateUpdated":"2026-05-27T12:17:05.666Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-05-13T15:03:33.083Z"},"containers":{"cna":{"title":"quota: fix livelock between quotactl and freeze_super","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 && 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\" &\n  # taskset -c 3 bash -c \"while true; do quotaon a_mount; \\\n    quotaoff a_mount; done\" &\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."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"576215cffdefc1f0ceebffd87abb390926e6b037","status":"affected","lessThan":"37ccd48cf35f3c8b9f2ea961a7b486b91eb71a82","versionType":"git"},{"version":"576215cffdefc1f0ceebffd87abb390926e6b037","status":"affected","lessThan":"414259caf81a397563fc9baca9c0ef856c4a97cf","versionType":"git"},{"version":"576215cffdefc1f0ceebffd87abb390926e6b037","status":"affected","lessThan":"02bb1500f1479750e6557c8044f6a2d7e9d30c12","versionType":"git"},{"version":"576215cffdefc1f0ceebffd87abb390926e6b037","status":"affected","lessThan":"53b2314b26b6640a3657cc924de63a1a8f26ac4d","versionType":"git"},{"version":"576215cffdefc1f0ceebffd87abb390926e6b037","status":"affected","lessThan":"77449e453dfc006ad738dec55374c4cbc056fd39","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/quota/quota.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.5","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.5","versionType":"semver"},{"version":"6.6.128","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.75","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.14","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"6.19.4","status":"unaffected","lessThanOrEqual":"6.19.*","versionType":"semver"},{"version":"7.0","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/quota/quota.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/37ccd48cf35f3c8b9f2ea961a7b486b91eb71a82"},{"url":"https://git.kernel.org/stable/c/414259caf81a397563fc9baca9c0ef856c4a97cf"},{"url":"https://git.kernel.org/stable/c/02bb1500f1479750e6557c8044f6a2d7e9d30c12"},{"url":"https://git.kernel.org/stable/c/53b2314b26b6640a3657cc924de63a1a8f26ac4d"},{"url":"https://git.kernel.org/stable/c/77449e453dfc006ad738dec55374c4cbc056fd39"}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-05-27T12:17:05.666Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.5","versionEndExcluding":"6.6.128"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.5","versionEndExcluding":"6.12.75"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.5","versionEndExcluding":"6.18.14"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.5","versionEndExcluding":"6.19.4"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.5","versionEndExcluding":"7.0"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}