From: Xiang Mei <xmei5@asu.edu> mainline inclusion from mainline-v7.3-rc1 commit 68d4d3e78150c7ed7d1195af63ad1e6ace30c661 category: bugfix bugzilla: https://atomgit.com/src-openeuler/kernel/issues/19048 CVE: CVE-2026-89778 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=... -------------------------------- 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 Fixes: 59bc055211b8 ("zisofs: Implement reading of compressed files when PAGE_CACHE_SIZE > compress block size") Reported-by: Weiming Shi <bestswngs@gmail.com> Assisted-by: Claude:claude-opus-4-8 Signed-off-by: Xiang Mei <xmei5@asu.edu> Link: https://patch.msgid.link/20260712234150.3213467-1-xmei5@asu.edu Signed-off-by: Jan Kara <jack@suse.cz> Conflicts: fs/isofs/compress.c [memzero_page() does not exist in this tree, so use memset(page_address(pages[i]) + off, 0, PAGE_SIZE - off) followed by flush_dcache_page(), matching the pre-existing page clearing idiom here.] Co-authored-by: BackportAgent@deepseek-v4.1-flash Signed-off-by: Hulk Robot <hulkrobot@huawei.com> Signed-off-by: Ran Hongyun <ranhongyun1@huawei.com> Signed-off-by: Lin Yujun <linyujun809@h-partners.com> --- fs/isofs/compress.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/fs/isofs/compress.c b/fs/isofs/compress.c index 10205ececc27..60f02e10dbef 100644 --- a/fs/isofs/compress.c +++ b/fs/isofs/compress.c @@ -68,17 +68,19 @@ static loff_t zisofs_uncompress_block(struct inode *inode, loff_t block_start, return 0; } /* Empty block? */ if (block_size == 0) { for ( i = 0 ; i < pcount ; i++ ) { + unsigned int off = i ? 0 : poffset; + if (!pages[i]) continue; - memset(page_address(pages[i]), 0, PAGE_SIZE); + memset(page_address(pages[i]) + off, 0, PAGE_SIZE - off); flush_dcache_page(pages[i]); SetPageUptodate(pages[i]); } - return ((loff_t)pcount) << PAGE_SHIFT; + return (((loff_t)pcount) << PAGE_SHIFT) - poffset; } /* Because zlib is not thread-safe, do all the I/O at the top. */ blocknum = block_start >> bufshift; bhs = kcalloc(needblocks + 1, sizeof(*bhs), GFP_KERNEL); -- 2.34.1