DEBIAN-CVE-2026-89778

In the Linux kernel, the following vulnerability has been resolved:  isofs: fix out-of-bounds page array access on empty zisofs block  zisofsuncompressblock()'s empty-block fast path returns pcount << PAGESHIFT, ignoring the incoming poffset, unlike the decompression path which returns bytes produced relative to poffset. zisofsfillpages() uses that return to advance its page cursor, so when the zisofs block size is below PAGESIZE 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 PAGESHIFT; 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, PAGESIZE) of the first page, matching the decompression path. The page-aligned case (poffset == 0) is unaffected.    BUG: KASAN: slab-out-of-bounds in zisofsreadfolio (fs/isofs/compress.c:290)   Read of size 8 at addr ffff88800f5eac48 by task exploit/142    zisofsreadfolio (fs/isofs/compress.c:290)    readpages (mm/readahead.c:184)    ...    filemapread (mm/filemap.c:2814)    vfsread (fs/readwrite.c:574)    _x64syspread64 (fs/readwrite.c:769)    dosyscall64 (arch/x86/entry/syscall64.c:94)    entrySYSCALL64afterhwframe (arch/x86/entry/entry64.S:121)   The buggy address is located 0 bytes to the right of the   allocated 8-byte region in the kmalloc-8 cache