Vulnerability CVE-2024-40943
Published: 2024-07-12

Description:
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.

 References:
https://git.kernel.org/stable/c/3c26b5d21b1239e9c7fd31ba7d9b2d7bdbaa68d9
https://git.kernel.org/stable/c/e8e2db1adac47970a6a9225f3858e9aa0e86287f
https://git.kernel.org/stable/c/050ce8af6838c71e872e982b50d3f1bec21da40e
https://git.kernel.org/stable/c/38825ff9da91d2854dcf6d9ac320a7e641e10f25
https://git.kernel.org/stable/c/ea042dc2bea19d72e37c298bf65a9c341ef3fff3
https://git.kernel.org/stable/c/3c361f313d696df72f9bccf058510e9ec737b9b1
https://git.kernel.org/stable/c/117b9c009b72a6c2ebfd23484354dfee2d9570d2
https://git.kernel.org/stable/c/952b023f06a24b2ad6ba67304c4c84d45bea2f18
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