CVE-2021-46972

In the Linux kernel, the following vulnerability has been resolved:<br /> <br /> ovl: fix leaked dentry<br /> <br /> Since commit 6815f479ca90 ("ovl: use only uppermetacopy state in<br /> ovl_lookup()"), overlayfs doesn&amp;#39;t put temporary dentry when there is a<br /> metacopy error, which leads to dentry leaks when shutting down the related<br /> superblock:<br /> <br /> overlayfs: refusing to follow metacopy origin for (/file0)<br /> ...<br /> BUG: Dentry (____ptrval____){i=3f33,n=file3} still in use (1) [unmount of overlay overlay]<br /> ...<br /> WARNING: CPU: 1 PID: 432 at umount_check.cold+0x107/0x14d<br /> CPU: 1 PID: 432 Comm: unmount-overlay Not tainted 5.12.0-rc5 #1<br /> ...<br /> RIP: 0010:umount_check.cold+0x107/0x14d<br /> ...<br /> Call Trace:<br /> d_walk+0x28c/0x950<br /> ? dentry_lru_isolate+0x2b0/0x2b0<br /> ? __kasan_slab_free+0x12/0x20<br /> do_one_tree+0x33/0x60<br /> shrink_dcache_for_umount+0x78/0x1d0<br /> generic_shutdown_super+0x70/0x440<br /> kill_anon_super+0x3e/0x70<br /> deactivate_locked_super+0xc4/0x160<br /> deactivate_super+0xfa/0x140<br /> cleanup_mnt+0x22e/0x370<br /> __cleanup_mnt+0x1a/0x30<br /> task_work_run+0x139/0x210<br /> do_exit+0xb0c/0x2820<br /> ? __kasan_check_read+0x1d/0x30<br /> ? find_held_lock+0x35/0x160<br /> ? lock_release+0x1b6/0x660<br /> ? mm_update_next_owner+0xa20/0xa20<br /> ? reacquire_held_locks+0x3f0/0x3f0<br /> ? __sanitizer_cov_trace_const_cmp4+0x22/0x30<br /> do_group_exit+0x135/0x380<br /> __do_sys_exit_group.isra.0+0x20/0x20<br /> __x64_sys_exit_group+0x3c/0x50<br /> do_syscall_64+0x45/0x70<br /> entry_SYSCALL_64_after_hwframe+0x44/0xae<br /> ...<br /> VFS: Busy inodes after unmount of overlay. Self-destruct in 5 seconds. Have a nice day...<br /> <br /> This fix has been tested with a syzkaller reproducer.