{"cve":"CVE-2026-64359","nvd":{"published":"2026-07-25T10:17:18.377","modified":"2026-09-04T15:57:39.937","status":"Analyzed","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nnilfs2: reject CLEAN_SEGMENTS ioctl with out-of-range segment numbers\n\nSyzbot reported a hung task in nilfs_transaction_begin() where multiple\ntasks performing chmod() on a nilfs2 mount blocked for over 143 seconds\nwaiting to acquire ns_segctor_sem for read:\n\n  INFO: task syz.0.17:5918 blocked for more than 143 seconds.\n  Call Trace:\n   schedule+0x164/0x360\n   rwsem_down_read_slowpath+0x6d9/0x940\n   down_read+0x99/0x2e0\n   nilfs_transaction_begin+0x364/0x710 fs/nilfs2/segment.c:221\n   nilfs_setattr+0x124/0x2c0 fs/nilfs2/inode.c:921\n   notify_change+0xc1a/0xf40\n   chmod_common+0x273/0x4a0\n   do_fchmodat+0x12d/0x230\n\nThe writer holding ns_segctor_sem was a concurrent\nNILFS_IOCTL_CLEAN_SEGMENTS caller, stuck inside printk while emitting\nper-element warnings from nilfs_sufile_updatev():\n\n   __nilfs_msg+0x373/0x450 fs/nilfs2/super.c:78\n   nilfs_sufile_updatev+0x21c/0x6d0 fs/nilfs2/sufile.c:186\n   nilfs_sufile_freev fs/nilfs2/sufile.h:93 [inline]\n   nilfs_free_segments fs/nilfs2/segment.c:1140 [inline]\n   nilfs_segctor_collect_blocks fs/nilfs2/segment.c:1261 [inline]\n   nilfs_segctor_do_construct+0x1f55/0x76c0\n   nilfs_clean_segments+0x3bd/0xa50\n   nilfs_ioctl_clean_segments fs/nilfs2/ioctl.c:922 [inline]\n   nilfs_ioctl+0x261f/0x2780\n\nThe root cause is that user-supplied segment numbers are not validated\nbefore nilfs_clean_segments() begins doing work; the range check on\neach segnum is performed deep inside the call chain by\nnilfs_sufile_updatev(), which emits a nilfs_warn() per invalid entry\nwhile still holding the segctor lock and the sufile mi_sem.  Under load\n(repeated invocations across multiple mounts saturating the global\nprintk path), the cumulative printk latency keeps ns_segctor_sem held\nlong enough to trip the hung_task watchdog, blocking concurrent\noperations such as chmod() that need ns_segctor_sem for read.\n\nFix by validating the contents of kbufs[4] in nilfs_clean_segments()\nimmediately after acquiring ns_segctor_sem via nilfs_transaction_lock().\nHolding ns_segctor_sem serializes the check against\nnilfs_ioctl_resize(), which can modify ns_nsegments, so the validation\nuses a consistent value.  Out-of-range segment numbers are rejected\nwith -EINVAL before any segment-cleaning work begins, so the bad\nentries never reach the per-element diagnostic path inside\nnilfs_sufile_updatev().","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H","score":5.5},"cwes":[],"references":["https://git.kernel.org/stable/c/0789f0a6710713254a08f3a7d2ecbb6d1cbcf0aa","https://git.kernel.org/stable/c/0e7a690fe435f8d5ea3feb7c1d8d73ba7e8b8aa9","https://git.kernel.org/stable/c/223463c488b0554212a94de971ea538eb2805fc7","https://git.kernel.org/stable/c/286f77d002a337735c0846d7480a82d9cda2aa31","https://git.kernel.org/stable/c/39607452b1400c7bf748f15122df4d058b768c5b"],"products":["linux:linux_kernel"],"source":"nvd","synced_at":"2026-10-19T22:46:40.600842820+00:00"},"epss":{"cve":"CVE-2026-64359","score":0.00123,"percentile":0.02013,"date":"2026-10-31"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}