GHSA-VFMJ-8PGC-H88M
Vulnerability from github – Published: 2026-09-16 09:30 – Updated: 2026-09-16 15:30In the Linux kernel, the following vulnerability has been resolved:
isofs: fix out-of-bounds page array access on empty zisofs block
zisofs_uncompress_block()'s empty-block fast path returns pcount << PAGE_SHIFT, ignoring the incoming poffset, unlike the decompression path which returns bytes produced relative to poffset. zisofs_fill_pages() uses that return to advance its page cursor, so when the zisofs block size is below PAGE_SIZE and a sub-page block leaves poffset partway into a page, a following empty block over-counts and advances pages[] one element past its end, after which "if (poffset && *pages)" reads pages[1] out of bounds. rock.c only rejects a block-size shift > 17, so a crafted "ZF" Rock Ridge record can set it below PAGE_SHIFT; the bug is reached by an ordinary read() of a compressed file on such a mounted ISO9660 image.
Return the byte count relative to poffset and zero only [poffset, PAGE_SIZE) of the first page, matching the decompression path. The page-aligned case (poffset == 0) is unaffected.
BUG: KASAN: slab-out-of-bounds in zisofs_read_folio (fs/isofs/compress.c:290) Read of size 8 at addr ffff88800f5eac48 by task exploit/142 zisofs_read_folio (fs/isofs/compress.c:290) read_pages (mm/readahead.c:184) ... filemap_read (mm/filemap.c:2814) vfs_read (fs/read_write.c:574) __x64_sys_pread64 (fs/read_write.c:769) do_syscall_64 (arch/x86/entry/syscall_64.c:94) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121) The buggy address is located 0 bytes to the right of the allocated 8-byte region in the kmalloc-8 cache
{
"affected": [],
"aliases": [
"CVE-2026-89778"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-09-16T09:17:08Z",
"severity": "CRITICAL"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nisofs: fix out-of-bounds page array access on empty zisofs block\n\nzisofs_uncompress_block()\u0027s empty-block fast path returns\npcount \u003c\u003c PAGE_SHIFT, ignoring the incoming poffset, unlike the\ndecompression path which returns bytes produced relative to poffset.\nzisofs_fill_pages() uses that return to advance its page cursor, so when\nthe zisofs block size is below PAGE_SIZE and a sub-page block leaves\npoffset partway into a page, a following empty block over-counts and\nadvances pages[] one element past its end, after which\n\"if (poffset \u0026\u0026 *pages)\" reads pages[1] out of bounds. rock.c only\nrejects a block-size shift \u003e 17, so a crafted \"ZF\" Rock Ridge record can\nset it below PAGE_SHIFT; the bug is reached by an ordinary read() of a\ncompressed file on such a mounted ISO9660 image.\n\nReturn the byte count relative to poffset and zero only\n[poffset, PAGE_SIZE) of the first page, matching the decompression path.\nThe page-aligned case (poffset == 0) is unaffected.\n\n BUG: KASAN: slab-out-of-bounds in zisofs_read_folio (fs/isofs/compress.c:290)\n Read of size 8 at addr ffff88800f5eac48 by task exploit/142\n zisofs_read_folio (fs/isofs/compress.c:290)\n read_pages (mm/readahead.c:184)\n ...\n filemap_read (mm/filemap.c:2814)\n vfs_read (fs/read_write.c:574)\n __x64_sys_pread64 (fs/read_write.c:769)\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 The buggy address is located 0 bytes to the right of the\n allocated 8-byte region in the kmalloc-8 cache",
"id": "GHSA-vfmj-8pgc-h88m",
"modified": "2026-09-16T15:30:57Z",
"published": "2026-09-16T09:30:29Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-89778"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/68d4d3e78150c7ed7d1195af63ad1e6ace30c661"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/85904076cece72ee3194646ad7ac8e6659d999aa"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/8b994ac5778a725982fd6a8a3afcaa068d4a93e3"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/9c6eace8d07e90f038c89eb3b756d65a7e259d48"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/ad3249cdf9d4ba34bb8b1ff3956a4020fdfb5b0a"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/cd616aa0449a772a6956abf03358f0ff31720580"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/f03425dcbe04aec3c27b9917e97d7d23a2908dda"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
"type": "CVSS_V3"
}
]
}
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