smb: client: fix busy dentry warning on unmount after DIO

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Summary

CVECVE-2026-72315
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-08-15 06:22:04 UTC
Updated2026-10-03 11:17:37 UTC
DescriptionIn 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.

Risk And Classification

Primary CVSS: v3.1 7.8 HIGH from 416baaa9-dc9f-4396-8d5f-8c081fb06d67

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

EPSS: 0.001750000 probability, percentile 0.063440000 (date 2026-10-05)

VersionSourceTypeScoreSeverityVector
3.1416baaa9-dc9f-4396-8d5f-8c081fb06d67Secondary7.8HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
3.1CNADECLARED7.8HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

CVSS v3.1 Breakdown

Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 0e4b8faaaebe3137bec5723ef2b3cb0437fb38fd f7748b551010c021d92f0125e37f32ac0c376d8a git Not specified
CNA Linux Linux affected f655467a9973f964b267871e5fef533ad5014494 9fc87899276af941ecf3045798887db7deb85605 git Not specified
CNA Linux Linux affected 340cea84f691c5206561bb2e0147158fe02070be f0eac9c3c3711f24efc2aaf12b8ec3e54a38c214 git Not specified
CNA Linux Linux affected 340cea84f691c5206561bb2e0147158fe02070be 75f5c412fa867efa0bf9b646bffe0d912109e84a git Not specified
CNA Linux Linux affected 708c276f516d27beaded7f372ac8111cee43926c git Not specified
CNA Linux Linux affected 0629a1a187e424373364d681b42b101894bdb548 git Not specified
CNA Linux Linux affected 30afc6ea72cc6cf7c8d579e79b64232801c38d08 git Not specified
CNA Linux Linux affected 6.12.78 6.12.112 semver Not specified
CNA Linux Linux affected 6.18.20 6.18.54 semver Not specified
CNA Linux Linux affected 6.1.167 6.2 semver Not specified
CNA Linux Linux affected 6.6.130 6.7 semver Not specified
CNA Linux Linux affected 6.19.10 6.20 semver Not specified
CNA Linux Linux affected 7.0 Not specified
CNA Linux Linux unaffected 7.0 semver Not specified
CNA Linux Linux unaffected 6.12.112 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.54 6.18.* semver Not specified
CNA Linux Linux unaffected 7.1.5 7.1.* semver Not specified
CNA Linux Linux unaffected 7.2 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/9fc87899276af941ecf3045798887db7deb85605 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/75f5c412fa867efa0bf9b646bffe0d912109e84a 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/f0eac9c3c3711f24efc2aaf12b8ec3e54a38c214 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/f7748b551010c021d92f0125e37f32ac0c376d8a 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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