CVE-2026-64108cifs: Fix busy dentry used after unmounting

Official description

In the Linux kernel, the following vulnerability has been resolved: cifs: Fix busy dentry used after unmounting Since commit 340cea84f691c ("cifs: open files should not hold ref on superblock"), cifs file only holds the dentry ref_cnt, the cifs file close work(cfile->deferred) could be executed after unmounting, which will trigger a warning in generic_shutdown_super: BUG: Dentry 00000000a14a6845{i=c,n=file} still in use (1) [unmount of cifs cifs] The detailed processs is: process A process B kworker fd = open(PATH) vfs_open file->__f_path = *path // dentry->d_lockref.count = 1 cifs_open cifs_new_fileinfo cfile->dentry = dget(dentry) // dentry->d_lockref.count = 2 close(fd) __fput cifs_close queue_delayed_work(deferredclose_wq, cfile->deferred) dput(dentry) // dentry->d_lockref.count = 1 smb2_deferred_work_close _cifsFileInfo_put list_del(&cifs_file->flist) umount cleanup_mnt deactivate_super cifs_kill_sb cifs_close_all_deferred_files_sb cifs_close_all_deferred_files // cannot find cfile, skip _cifsFileInfo_put kill_anon_super generic_shutdown_super shrink_dcache_for_umount umount_check WARN ! // dentry->d_lockref.count = 1 cifsFileInfo_put_final dput(cifs_file->dentry) // dentry->d_lockref.count = 0 Fix it by flushing 'deferredclose_wq' before calling kill_anon_super. Fetch a reproducer in https://bugzilla.kernel.org/show_bug.cgi?id=221548.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/c7364cea52531534676b9f7dbc0a477c11f4c050
• https://git.kernel.org/stable/c/bdc349a87f1fb02c18c4071858a06542bfea783d
• https://git.kernel.org/stable/c/f2deaa2f409a4598eaa10f2a93a676c0632af248
• https://git.kernel.org/stable/c/5e7d9d0805e58fa3760894e73115b7a74024fd07
• https://git.kernel.org/stable/c/e1ffa6cf662383f95816eed1b623429d82675e75
• https://git.kernel.org/stable/c/c68337442f03953237a94577beb468ab2662a851