Bug 2535065 (CVE-2026-89778) - CVE-2026-89778 kernel: isofs: fix out-of-bounds page array access on empty zisofs block
Summary: CVE-2026-89778 kernel: isofs: fix out-of-bounds page array access on empty zi...
Keywords:
Status: NEW
Alias: CVE-2026-89778
Product: Security Response
Classification: Other
Component: vulnerability
Version: unspecified
Hardware: All
OS: Linux
low
low
Target Milestone: ---
Assignee: Product Security DevOps Team
QA Contact:
URL:
Whiteboard:
Depends On:
Blocks:
TreeView+ depends on / blocked
 
Reported: 2026-09-16 09:11 UTC by OSIDB Bzimport
Modified: 2026-10-16 12:56 UTC (History)
17 users (show)

Fixed In Version:
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Description OSIDB Bzimport 2026-09-16 09:11:02 UTC
In 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


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