{"schema":"threatline.record/2","record":{"id":"CVE-2026-99180","aliases":[],"summary":"unicode: free the map after a grace period","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nunicode: free the map after a grace period\n\ngeneric_ci_d_hash() and generic_ci_d_compare() read sb->s_encoding and\ndereference the unicode map while a pathwalk in rcu mode holds nothing\nbut rcu_read_lock(). The filesystems that use them, ext4, f2fs and\ntmpfs, drop the map with utf8_unload() from ->put_super(), which runs\nwhen the last reference to the mount goes away. A lookup that is still\ninside such a filesystem at that point reads a freed map.\n\nWith a pathwalk held up in utf8_casefold_hash() while the last reference\nto a casefolded tmpfs goes away:\n\n  BUG: KASAN: slab-use-after-free in utf8nlookup+0x74c/0x950\n  Read of size 8 at addr ff110001030fe658 by task walker/98\n  Call Trace:\n   <TASK>\n   utf8nlookup+0x74c/0x950\n   utf8byte+0x160/0x1560\n   utf8_casefold_hash+0x167/0x230\n   generic_ci_d_hash+0xdd/0x1c0\n   link_path_walk+0x11ad/0x1d30\n   path_lookupat+0x63/0xb00\n   filename_lookup+0x1f1/0x5b0\n   vfs_statx+0xd7/0x3b0\n  [...]\n  Allocated by task 94:\n   __kmalloc_cache_noprof+0x249/0x560\n   utf8_load+0x4e/0x570\n   shmem_parse_opt_casefold.isra.0+0x92/0x270\n  [...]\n  Freed by task 97:\n   kfree+0x1db/0x5b0\n   shmem_put_super+0x72/0x170\n   generic_shutdown_super+0x14c/0x530\n   kill_anon_super+0x3a/0x60\n   deactivate_locked_super+0x9c/0xf0\n   cleanup_mnt+0x9f/0x130\n\nSo far that has been hard to hit. umount(2) waits for a grace period\nin namespace_unlock() before it drops the mount, so only a mount whose\nlast reference goes away elsewhere, like the close of a file or a chdir\nout of a lazily unmounted directory, can race a walker. So it is\nreachable.\n\nDelay the free until a grace period has passed. The map and the data\ntable it holds a reference to then outlive any pathwalk that found the\nsuperblock before the mount went away. The reference on the data table\nmodule is dropped from the rcu callback as well. utf8-core is built in\nwhenever CONFIG_UNICODE is set, so there is no module exit that would\nhave to wait for the callbacks.\n\nOverlayfs points the s_encoding of an overlay at the map of its first\nlayer without taking a reference of its own. That stays correct. The\nlayer is held by the overlay, so its map is dropped only after the\noverlay is gone.","categories":["Operating systems"],"product":"Linux","vendor":"Linux","ecosystem":null,"affected_ranges":[{"source":"CVE List","source_url":"https://www.cve.org/CVERecord?id=CVE-2026-99180","source_modified_at":"2026-10-28T10:35:33.578Z","fetched_at":"2026-10-28T15:55:58.673066Z","product":"Linux","vendor":"Linux","versions":[{"version":"b886ee3e778ec2ad43e276fd378ab492cf6819b7","lessThan":"2b54d3c971a1e5df3c9b0bcc10311ae6c29e79d8","status":"affected","versionType":"git"},{"version":"b886ee3e778ec2ad43e276fd378ab492cf6819b7","lessThan":"6560c3d9a6925e3747d9ad8463e16010c31ba715","status":"affected","versionType":"git"},{"version":"b886ee3e778ec2ad43e276fd378ab492cf6819b7","lessThan":"a96c5299bd7305eb984377681eb3222a57376405","status":"affected","versionType":"git"}],"defaultStatus":"unaffected"},{"source":"CVE List","source_url":"https://www.cve.org/CVERecord?id=CVE-2026-99180","source_modified_at":"2026-10-28T10:35:33.578Z","fetched_at":"2026-10-28T15:55:58.673066Z","product":"Linux","vendor":"Linux","versions":[{"version":"5.2","status":"affected"},{"version":"0","lessThan":"5.2","status":"unaffected","versionType":"semver"},{"version":"6.18.59","lessThanOrEqual":"6.18.*","status":"unaffected","versionType":"semver"},{"version":"7.2.13","lessThanOrEqual":"7.2.*","status":"unaffected","versionType":"semver"},{"version":"7.3","lessThanOrEqual":"*","status":"unaffected","versionType":"original_commit_for_fix"}],"defaultStatus":"affected"}],"fixed_versions":[{"source":"CVE List","source_url":"https://www.cve.org/CVERecord?id=CVE-2026-99180","source_modified_at":"2026-10-28T10:35:33.578Z","fetched_at":"2026-10-28T15:55:58.673066Z","package":{"name":"Linux","ecosystem":null},"version":"2b54d3c971a1e5df3c9b0bcc10311ae6c29e79d8","basis":"first unaffected version stated in the CVE record"},{"source":"CVE List","source_url":"https://www.cve.org/CVERecord?id=CVE-2026-99180","source_modified_at":"2026-10-28T10:35:33.578Z","fetched_at":"2026-10-28T15:55:58.673066Z","package":{"name":"Linux","ecosystem":null},"version":"6560c3d9a6925e3747d9ad8463e16010c31ba715","basis":"first unaffected version stated in the CVE record"}],"cvss":null,"severity":null,"kev":{"listed":false},"epss":{"probability":null,"percentile":null,"score_date":null},"published_at":"2026-10-28T10:35:33.578Z","modified_at":"2026-10-28T10:35:33.578Z","provenance":[{"source":"CVE List","url":"https://www.cve.org/CVERecord?id=CVE-2026-99180","fetched_at":"2026-10-28T15:55:58.673066Z","source_modified_at":"2026-10-28T10:35:33.578Z"}],"sources":["CVE List"],"references":[{"source":"CVE List","url":"https://git.kernel.org/stable/c/2b54d3c971a1e5df3c9b0bcc10311ae6c29e79d8"},{"source":"CVE List","url":"https://git.kernel.org/stable/c/6560c3d9a6925e3747d9ad8463e16010c31ba715"},{"source":"CVE List","url":"https://git.kernel.org/stable/c/a96c5299bd7305eb984377681eb3222a57376405"}],"locations":[],"motoko_assessment":{"status":"requires_architecture_review","automatic_remediation":false},"cve_state":"PUBLISHED","classification":{"method":"product-first software-layer rules","rules_version":"2.1","matched_on":"product","confidence":"heuristic","reviewed":false},"change_timestamp":"2026-10-28T10:35:33.578Z","content_hash":"f3e0c6f01a6564b2ae99d3cd4fe5adc17335c1bf4428406ed177e8ffead94011"}}