CVE-2021-46972

In the Linux kernel, the following vulnerability has been resolved: ovl:
fix leaked dentry Since commit 6815f479ca90 (“ovl: use only uppermetacopy
state in ovl_lookup()”), overlayfs doesn’t put temporary dentry when there
is a metacopy error, which leads to dentry leaks when shutting down the
related superblock: overlayfs: refusing to follow metacopy origin for
(/file0) … BUG: Dentry (ptrval){i=3f33,n=file3} still in use (1)
[unmount of overlay overlay] … WARNING: CPU: 1 PID: 432 at
umount_check.cold+0x107/0x14d CPU: 1 PID: 432 Comm: unmount-overlay Not
tainted 5.12.0-rc5 #1 … RIP: 0010:umount_check.cold+0x107/0x14d … Call
Trace: d_walk+0x28c/0x950 ? dentry_lru_isolate+0x2b0/0x2b0 ?
__kasan_slab_free+0x12/0x20 do_one_tree+0x33/0x60
shrink_dcache_for_umount+0x78/0x1d0 generic_shutdown_super+0x70/0x440
kill_anon_super+0x3e/0x70 deactivate_locked_super+0xc4/0x160
deactivate_super+0xfa/0x140 cleanup_mnt+0x22e/0x370 __cleanup_mnt+0x1a/0x30
task_work_run+0x139/0x210 do_exit+0xb0c/0x2820 ?
__kasan_check_read+0x1d/0x30 ? find_held_lock+0x35/0x160 ?
lock_release+0x1b6/0x660 ? mm_update_next_owner+0xa20/0xa20 ?
reacquire_held_locks+0x3f0/0x3f0 ?
__sanitizer_cov_trace_const_cmp4+0x22/0x30 do_group_exit+0x135/0x380
__do_sys_exit_group.isra.0+0x20/0x20 __x64_sys_exit_group+0x3c/0x50
do_syscall_64+0x45/0x70 entry_SYSCALL_64_after_hwframe+0x44/0xae … VFS:
Busy inodes after unmount of overlay. Self-destruct in 5 seconds. Have a
nice day… This fix has been tested with a syzkaller reproducer.