erofs: fix use-after-free on sbi->sync_decompress

In the Linux kernel, the following vulnerability has been resolved: erofs: fix use-after-free on sbi->sync_decompress z_erofs_decompress_kickoff() can race with filesystem unmount, causing a use-after-free on sbi->sync_decompress. When I/O completes, z_erofs_endio() calls z_erofs_decompress_kickoff() to queue z_erofs_decompressqueue_work() asynchronously. Then, after all folios are unlocked, unmount workflow can proceed and sbi will be freed before accessing to sbi->sync_decompress. Thread (unmount) I/O completion kworker queue_work z_erofs_decompressqueue_work (all folios are unlocked) cleanup_mnt .. erofs_kill_sb erofs_sb_free kfree(sbi) access sbi->sync_decompress // UAF!!