Linux vulnerability

What happened

In the Linux kernel, the following vulnerability has been resolved: smb: client: fix busy dentry warning on unmount after DIO Commit c68337442f03 ("cifs: Fix busy dentry used after unmounting") fixed the issue in cifs where deferred close of a file led to a dentry reference count not being released in umount, by flushing deferredclose_wq in cifs_kill_sb() to solve it. However, the cifs DIO path suffers from the same busy-dentry problem caused by a delayed dentry reference-count release: [dio] [cifsd] [close + umount] netfs_unbuffered_write_iter_locked ... cifs_demultiplex_thread netfs_unbuffered_write cifs_issue_write netfs_wait_for_in_progress_stream [1] ... netfs_write_subrequest_terminated netfs_subreq_clear_in_progress netfs_wake_collector // wake [1] netfs_put_subrequest netfs_put_request queue_work(system_dfl_wq, xxx) [2] // dio write return cifs_close _cifsFileInfo_put // cfile->count 2->1 --cfile->count [3] // umount cifs_kill_sb kill_anon_super // warning triggered! shrink_dcache_for_umount [4] [system_dfl_wq] [5] netfs_free_request ... _cifsFileInfo_put // cfile->count 1->0 --cfile->count queue_work(fileinfo_put_wq, xxx) [fileinfo_put_wq] [6] cifsFileInfo_put_work cifsFileInfo_put_final dput If the umount path is triggered before [5], it results warning: BUG: Dentry 00000000eab1f070{i=9a917b66ae404fec,n=test} still in use (1) [unmount of cifs cifs] The existing per-inode ictx->io_count wait in cifs_evict_inode() does not help: it lives in the inode eviction path, which runs after shrink_dcache_for_umount() has already warned about the busy dentries. Fix it by adding a per-superblock outstanding-rreq counter that is incremented in cifs_init_request() and decremented in cifs_free_request(). In cifs_kill_sb(), before kill_anon_super(), wait for this counter to reach 0 - which guarantees that all cleanup_work for this sb have run and thus all relevant cfile puts are queued on fileinfo_put_wq or serverclose_wq. Then drain the workqueue so the dentry refs are dropped. This is a targeted wait, not a flush of the system-wide system_dfl_wq.

Affected versions

Linux: 0e4b8faaaebe3137bec5723ef2b3cb0437fb38fd through before f7748b551010c021d92f0125e37f32ac0c376d8a (git); f655467a9973f964b267871e5fef533ad5014494 through before 9fc87899276af941ecf3045798887db7deb85605 (git); 340cea84f691c5206561bb2e0147158fe02070be through before f0eac9c3c3711f24efc2aaf12b8ec3e54a38c214 (git); 340cea84f691c5206561bb2e0147158fe02070be through before 75f5c412fa867efa0bf9b646bffe0d912109e84a (git); 708c276f516d27beaded7f372ac8111cee43926c (git); 0629a1a187e424373364d681b42b101894bdb548 (git); 30afc6ea72cc6cf7c8d579e79b64232801c38d08 (git); 6.12.78 through before 6.12.112 (semver); 6.18.20 through before 6.18.54 (semver); 6.1.167 through before 6.2 (semver); 6.6.130 through before 6.7 (semver); 6.19.10 through before 6.20 (semver); 7.0 Fixed: See vendor advisory.

Why it matters

Review the vendor advisory and exposure of the affected product to determine operational impact.

Detection & mitigation

• Apply vendor-provided updates or mitigations.
• Review affected product exposure and access logs.