Bug 2541214 (CVE-2026-97557)

Summary: CVE-2026-97557 kernel: smb: client: avoid leaking refcount in cifs_queue_oplock_break()
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: akhatavk, aos-team-art-private, asdas, dpaolell, jdelft, jupierce, lgarciaa, mbiarnes, ppalepu, ppostler, prdhamdh, rhel-process-autobot, sghai, sidsharm, suppawar, vlaad, watson-tool-maintainers
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
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Doc Text:
A flaw was found in the Linux kernel's Server Message Block (SMB) client. This flaw allows a remote or slow-responding SMB server to cause a Denial of Service (DoS) through a kernel crash. When handling opportunistic lock (oplock) break requests, the client can leak file reference counters if a new notification arrives while earlier work is still queued. This leaked reference leaves file system structures marked as in use, causing the kernel to crash when unmounting the file system.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
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Description OSIDB Bzimport 2026-09-25 11:03:27 UTC 
In the Linux kernel, the following vulnerability has been resolved:

smb: client: avoid leaking refcount in cifs_queue_oplock_break()

cifs_queue_oplock_break() unconditionally takes a reference on the
target file before queueing cifs_oplock_break(). Only that work item
decreases the reference counter again.

If another oplock break arrives while that work is still queued,
queue_work() will return false and not queue this second work item. As a
result, we will never reach the point to drop the file reference again
and are leaking this reference. This can be triggered when interacting
with a slow-responding server.

As a result, later unmount operations for this file system will fail with

  BUG: Dentry ... still in use (1) [unmount of cifs cifs]
  VFS: Busy inodes after unmount of cifs (cifs)
  kernel BUG at fs/super.c:777!

Fix this by only incrementing the reference count if the work has been
queued successfully. Taking it after queue_work() is safe because all
three callers hold tcon->open_file_lock across the call and
_cifsFileInfo_put() decrements under that same lock, so a worker that
starts the handler in the window cannot drop the reference before it has
been taken.
Comment 1 gkamathe 2026-09-29 02:29:45 UTC 
Upstream advisory:
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-97557.mbox