{"id":"CVE-2026-89787","summary":"ext4: check dir entry fits before reading the hash trailer in ext4_search_dir()","details":"In the Linux kernel, the following vulnerability has been resolved:\n\next4: check dir entry fits before reading the hash trailer in ext4_search_dir()\n\nFor casefolded encrypted directories ext4 stores an 8-byte hash trailer\nafter the name (EXT4_DIRENT_HASHES()), at an offset derived from\nde-\u003ename_len.  On the sb_no_casefold_compat_fallback() path ext4_match()\nreads that trailer, but ext4_search_dir()'s by-hand pre-check only tests\nde-\u003ename + de-\u003ename_len \u003c= dlimit, which proves the name fits, not the\nrounded trailer.  A crafted entry whose name ends at the block boundary\npasses the check while EXT4_DIRENT_HASHES(de) lands past the block end,\nso ext4_match() reads out of bounds on an ordinary lookup.  KASAN reports\nit as a use-after-free when the page after the directory block holds a\nfreed object:\n\n  BUG: KASAN: use-after-free in ext4_match (fs/ext4/namei.c:1435)\n  Read of size 4 at addr ffff888010458000 by task exploit\n  Call Trace:\n   ext4_match (fs/ext4/namei.c:1435)\n   ext4_search_dir (fs/ext4/namei.c:1470)\n   __ext4_find_entry (fs/ext4/namei.c:1268 fs/ext4/namei.c:1632)\n   ext4_lookup (fs/ext4/namei.c:1703 fs/ext4/namei.c:1769)\n   ...\n   filename_lookup (fs/namei.c:2842)\n   vfs_statx (fs/stat.c:353)\n   __do_sys_newfstatat (fs/stat.c:538)\n   do_syscall_64 (arch/x86/entry/syscall_64.c:94)\n   entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121)\n\nRequire, for hash-in-dirent directories, that the whole entry including\nthe rounded trailer fits before calling ext4_match().  This is the same\nbound ext4_check_dir_entry() already enforces via ext4_dir_rec_len(), so\nno well-formed entry is rejected.  The other caller, ext4_find_dest_de(),\nruns ext4_check_dir_entry() first and is unaffected.","modified":"2026-09-18T03:48:32.553479913Z","published":"2026-09-16T08:48:24.403Z","database_specific":{"cna_assigner":"Linux","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/89xxx/CVE-2026-89787.json"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/3933884bc3102898b458c53fbd1ac52eb9cdb8a4"},{"type":"WEB","url":"https://git.kernel.org/stable/c/4d20106c536b73c4a8a02652dc85e35898baebf7"},{"type":"WEB","url":"https://git.kernel.org/stable/c/61a395967de06edba58760e81907a272db749faa"},{"type":"WEB","url":"https://git.kernel.org/stable/c/83663c0b739480c00cfe785675db87520ec484ed"},{"type":"WEB","url":"https://git.kernel.org/stable/c/c7e6b863d298f56522d0d08554bbea7f142e6588"},{"type":"WEB","url":"https://git.kernel.org/stable/c/d8c184bec24b5a00ae96d704856d935eaded1685"},{"type":"WEB","url":"https://git.kernel.org/stable/c/e94676a08af6312aa72d8a981232b281f9bcfcf5"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/89xxx/CVE-2026-89787.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-89787"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"471fbbea7ff7061b2d6474665cb5a2ceb4fd6500"},{"fixed":"4d20106c536b73c4a8a02652dc85e35898baebf7"},{"fixed":"61a395967de06edba58760e81907a272db749faa"},{"fixed":"e94676a08af6312aa72d8a981232b281f9bcfcf5"},{"fixed":"d8c184bec24b5a00ae96d704856d935eaded1685"},{"fixed":"3933884bc3102898b458c53fbd1ac52eb9cdb8a4"},{"fixed":"83663c0b739480c00cfe785675db87520ec484ed"},{"fixed":"c7e6b863d298f56522d0d08554bbea7f142e6588"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-89787.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"5.13.0"},{"fixed":"5.15.221"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.16.0"},{"fixed":"6.1.188"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.2.0"},{"fixed":"6.6.157"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.7.0"},{"fixed":"6.12.110"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.13.0"},{"fixed":"6.18.52"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"7.2.6"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-89787.json"}}],"schema_version":"1.9.0"}