CVE-2026-89496: ocfs2: always run deallocs on copy-on-write completion

CVE-2026-89496: ocfs2: always run deallocs on copy-on-write completion

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

ocfs2: always run deallocs on copy-on-write completion

Local fuzzing of 6.12.94 has found the following memory leak
caused by doing 'copy_file_range()' within the same filesystem:

unreferenced object 0xffff88812192c980 (size 32):
  comm "syz.0.49", pid 12095, jiffies 4294964143
  hex dump (first 32 bytes):
    00 00 00 00 00 00 00 00 08 00 00 00 00 00 00 00  ................
    c0 c5 92 21 81 88 ff ff 00 02 00 00 00 06 00 00  ...!............
  backtrace (crc 7068d63f):
    kmemleak_alloc_recursive include/linux/kmemleak.h:42 [inline]
    slab_post_alloc_hook mm/slub.c:4152 [inline]
    slab_alloc_node mm/slub.c:4197 [inline]
    __kmalloc_cache_noprof+0x168/0x2c0 mm/slub.c:4358
    kmalloc_noprof include/linux/slab.h:878 [inline]
    ocfs2_find_per_slot_free_list fs/ocfs2/alloc.c:6618 [inline]
    ocfs2_cache_block_dealloc+0x155/0x4b0 fs/ocfs2/alloc.c:6786
    ocfs2_cache_extent_block_free fs/ocfs2/alloc.c:6819 [inline]
    ocfs2_unlink_path+0x286/0x450 fs/ocfs2/alloc.c:2613
    ocfs2_rotate_subtree_left fs/ocfs2/alloc.c:2779 [inline]
    __ocfs2_rotate_tree_left+0x1f6f/0x2da0 fs/ocfs2/alloc.c:2985
    ocfs2_rotate_tree_left+0x283/0xe00 fs/ocfs2/alloc.c:3237
    ocfs2_try_to_merge_extent+0xf56/0x1a20 fs/ocfs2/alloc.c:3825
    ocfs2_split_extent+0x15f4/0x2940 fs/ocfs2/alloc.c:5138
    ocfs2_clear_ext_refcount+0x2f6/0x550 fs/ocfs2/refcounttree.c:3098
    ocfs2_replace_clusters fs/ocfs2/refcounttree.c:3131 [inline]
    ocfs2_make_clusters_writable fs/ocfs2/refcounttree.c:3255 [inline]
    ocfs2_replace_cow+0x991/0x1660 fs/ocfs2/refcounttree.c:3349
    ocfs2_refcount_cow_hunk fs/ocfs2/refcounttree.c:3427 [inline]
    ocfs2_refcount_cow+0x5e1/0x9f0 fs/ocfs2/refcounttree.c:3470
    ocfs2_prepare_inode_for_write fs/ocfs2/file.c:2340 [inline]
    ocfs2_file_write_iter+0xbda/0x1880 fs/ocfs2/file.c:2451
    iter_file_splice_write+0x890/0xf60 fs/splice.c:743
    do_splice_from fs/splice.c:944 [inline]
    direct_splice_actor+0x232/0x480 fs/splice.c:1167
    splice_direct_to_actor+0x4b4/0xb60 fs/splice.c:1111
    do_splice_direct_actor fs/splice.c:1210 [inline]
    do_splice_direct+0x10f/0x1c0 fs/splice.c:1236
    do_sendfile+0x430/0xbf0 fs/read_write.c:1388

unreferenced object 0xffff88812192c5c0 (size 32):
  comm "syz.0.49", pid 12095, jiffies 4294964143
  hex dump (first 32 bytes):
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
    29 70 00 00 00 00 00 00 19 00 00 00 00 00 00 00  )p..............
  backtrace (crc afec850f):
    kmemleak_alloc_recursive include/linux/kmemleak.h:42 [inline]
    slab_post_alloc_hook mm/slub.c:4152 [inline]
    slab_alloc_node mm/slub.c:4197 [inline]
    __kmalloc_cache_noprof+0x168/0x2c0 mm/slub.c:4358
    kmalloc_noprof include/linux/slab.h:878 [inline]
    kzalloc_noprof include/linux/slab.h:1014 [inline]
    ocfs2_cache_block_dealloc+0x25c/0x4b0 fs/ocfs2/alloc.c:6793
    ocfs2_cache_extent_block_free fs/ocfs2/alloc.c:6819 [inline]
    ocfs2_unlink_path+0x286/0x450 fs/ocfs2/alloc.c:2613
    ocfs2_rotate_subtree_left fs/ocfs2/alloc.c:2779 [inline]
    __ocfs2_rotate_tree_left+0x1f6f/0x2da0 fs/ocfs2/alloc.c:2985
    ocfs2_rotate_tree_left+0x283/0xe00 fs/ocfs2/alloc.c:3237
    ocfs2_try_to_merge_extent+0xf56/0x1a20 fs/ocfs2/alloc.c:3825
    ocfs2_split_extent+0x15f4/0x2940 fs/ocfs2/alloc.c:5138
    ocfs2_clear_ext_refcount+0x2f6/0x550 fs/ocfs2/refcounttree.c:3098
    ocfs2_replace_clusters fs/ocfs2/refcounttree.c:3131 [inline]
    ocfs2_make_clusters_writable fs/ocfs2/refcounttree.c:3255 [inline]
    ocfs2_replace_cow+0x991/0x1660 fs/ocfs2/refcounttree.c:3349
    ocfs2_refcount_cow_hunk fs/ocfs2/refcounttree.c:3427 [inline]
    ocfs2_refcount_cow+0x5e1/0x9f0 fs/ocfs2/refcounttree.c:3470
    ocfs2_prepare_inode_for_write fs/ocfs2/file.c:2340 [inline]
    ocfs2_file_write_iter+0xbda/0x1880 fs/ocfs2/file.c:2451
    iter_file_splice_write+0x890/0xf60 fs/splice.c:743
    do_splice_from fs/splice.c:944 [inline]
    direct_splice_actor+0x232/0x480 fs/splice.c:1167
    splice_direct_to_actor+0x4b4/0xb60 fs/splice.c:1111
    do_splice_direct_actor fs/splice.c:1210 [inline]
    do_splice_direct+0x10f/0x1c0 fs/splice.c:1236
    do_sendfile+0x430/0xbf0 fs/read_write.c:1388

This happens when 'ocfs2_cache_block_dealloc()' called from
'ocfs2_cache_extent_block_free()' uses the suballocator to
schedule extent removal, so 'ocfs2_run_deallocs()' should
be run unconditionally to complete the removal with
'ocfs2_free_cached_blocks()'. An extra semi-automated static
analysis [1] suspects that the same scenario looks possible in
'ocfs2_attach_refcount_tree()' and 'ocfs2_reflink_remap_blocks()'
as well, but, since 'ocfs2_run_deallocs()' is a safe no-op for
an empty dealloc context, 'ocfs2_create_reflink_node()' and
'ocfs2_reflink_xattrs()' may be adjusted in the same way too,
thus keeping the code pattern consistent.

The Linux kernel CVE team has assigned CVE-2026-89496 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 2.6.32 with commit 6f70fa519976a379d72781d927cf8e5f5b05ec86 and fixed in 6.12.109 with commit 123c050eb96aae0bab74c9f06c6ad3de7992722b
	Issue introduced in 2.6.32 with commit 6f70fa519976a379d72781d927cf8e5f5b05ec86 and fixed in 6.18.50 with commit 71f07b7f90b3109c9098d1b9c8efbbeece5deb8a
	Issue introduced in 2.6.32 with commit 6f70fa519976a379d72781d927cf8e5f5b05ec86 and fixed in 7.2.4 with commit 09e93a60e18e83a630ff84ae00cb564bab96ab1f
	Issue introduced in 2.6.32 with commit 6f70fa519976a379d72781d927cf8e5f5b05ec86 and fixed in 7.3-rc1 with commit 82ea9d4fc05fb7a387db547c6a7c0aa6a3719616

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-89496
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	fs/ocfs2/refcounttree.c
	fs/ocfs2/xattr.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/123c050eb96aae0bab74c9f06c6ad3de7992722b
	https://git.kernel.org/stable/c/71f07b7f90b3109c9098d1b9c8efbbeece5deb8a
	https://git.kernel.org/stable/c/09e93a60e18e83a630ff84ae00cb564bab96ab1f
	https://git.kernel.org/stable/c/82ea9d4fc05fb7a387db547c6a7c0aa6a3719616