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.

Affected Software

References

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