GHSA-CXFP-66MH-JHVV
Vulnerability from github – Published: 2026-09-16 09:30 – Updated: 2026-09-16 09:30In the Linux kernel, the following vulnerability has been resolved:
ext4: check dir entry fits before reading the hash trailer in ext4_search_dir()
For casefolded encrypted directories ext4 stores an 8-byte hash trailer after the name (EXT4_DIRENT_HASHES()), at an offset derived from de->name_len. On the sb_no_casefold_compat_fallback() path ext4_match() reads that trailer, but ext4_search_dir()'s by-hand pre-check only tests de->name + de->name_len <= dlimit, which proves the name fits, not the rounded trailer. A crafted entry whose name ends at the block boundary passes the check while EXT4_DIRENT_HASHES(de) lands past the block end, so ext4_match() reads out of bounds on an ordinary lookup. KASAN reports it as a use-after-free when the page after the directory block holds a freed object:
BUG: KASAN: use-after-free in ext4_match (fs/ext4/namei.c:1435) Read of size 4 at addr ffff888010458000 by task exploit Call Trace: ext4_match (fs/ext4/namei.c:1435) ext4_search_dir (fs/ext4/namei.c:1470) __ext4_find_entry (fs/ext4/namei.c:1268 fs/ext4/namei.c:1632) ext4_lookup (fs/ext4/namei.c:1703 fs/ext4/namei.c:1769) ... filename_lookup (fs/namei.c:2842) vfs_statx (fs/stat.c:353) __do_sys_newfstatat (fs/stat.c:538) do_syscall_64 (arch/x86/entry/syscall_64.c:94) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121)
Require, for hash-in-dirent directories, that the whole entry including the rounded trailer fits before calling ext4_match(). This is the same bound ext4_check_dir_entry() already enforces via ext4_dir_rec_len(), so no well-formed entry is rejected. The other caller, ext4_find_dest_de(), runs ext4_check_dir_entry() first and is unaffected.
{
"affected": [],
"aliases": [
"CVE-2026-89787"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-09-16T09:17:09Z",
"severity": null
},
"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()\u0027s 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.",
"id": "GHSA-cxfp-66mh-jhvv",
"modified": "2026-09-16T09:30:30Z",
"published": "2026-09-16T09:30:30Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-89787"
},
{
"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"
}
],
"schema_version": "1.4.0",
"severity": []
}
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