CVE-2024-40943

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

ocfs2: fix races between hole punching and AIO+DIO

After commit "ocfs2: return real error code in ocfs2_dio_wr_get_block",

fstests/generic/300 become from always failed to sometimes failed:

========================================================================

[ 473.293420 ] run fstests generic/300

[ 475.296983 ] JBD2: Ignoring recovery information on journal

[ 475.302473 ] ocfs2: Mounting device (253,1) on (node local, slot 0) with ordered data mode.

[ 494.290998 ] OCFS2: ERROR (device dm-1): ocfs2_change_extent_flag: Owner 5668 has an extent at cpos 78723 which can no longer be found

[ 494.291609 ] On-disk corruption discovered. Please run fsck.ocfs2 once the filesystem is unmounted.

[ 494.292018 ] OCFS2: File system is now read-only.

[ 494.292224 ] (kworker/19:11,2628,19):ocfs2_mark_extent_written:5272 ERROR: status = -30

[ 494.292602 ] (kworker/19:11,2628,19):ocfs2_dio_end_io_write:2374 ERROR: status = -3

fio: io_u error on file /mnt/scratch/racer: Read-only file system: write offset=460849152, buflen=131072

=========================================================================

In __blockdev_direct_IO, ocfs2_dio_wr_get_block is called to add unwritten

extents to a list. extents are also inserted into extent tree in

ocfs2_write_begin_nolock. Then another thread call fallocate to puch a

hole at one of the unwritten extent. The extent at cpos was removed by

ocfs2_remove_extent(). At end io worker thread, ocfs2_search_extent_list

found there is no such extent at the cpos.

T1 T2 T3

inode lock

...

insert extents

...

inode unlock

ocfs2_fallocate

__ocfs2_change_file_space

inode lock

lock ip_alloc_sem

ocfs2_remove_inode_range inode

ocfs2_remove_btree_range

ocfs2_remove_extent

^---remove the extent at cpos 78723

...

unlock ip_alloc_sem

inode unlock

ocfs2_dio_end_io

ocfs2_dio_end_io_write

lock ip_alloc_sem

ocfs2_mark_extent_written

ocfs2_change_extent_flag

ocfs2_search_extent_list

^---failed to find extent

...

unlock ip_alloc_sem

In most filesystems, fallocate is not compatible with racing with AIO+DIO,

so fix it by adding to wait for all dio before fallocate/punch_hole like

ext4.