Bug 2468218 (CVE-2026-43376)

Summary: CVE-2026-43376 kernel: ksmbd: fix use-after-free by using call_rcu() for oplock_info
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
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Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in ksmbd in the Linux kernel. The `oplock_info` structure is immediately freed using `kfree()` without an RCU (Read-Copy-Update) grace period, even though it can still be accessed by readers. This improper memory deallocation can lead to a use-after-free vulnerability, particularly in the `opinfo_get()` function, where operations are performed on already freed memory. A local attacker could potentially exploit this to cause system instability or a denial of service.
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Description OSIDB Bzimport 2026-05-08 15:05:21 UTC 
In the Linux kernel, the following vulnerability has been resolved:

ksmbd: fix use-after-free by using call_rcu() for oplock_info

ksmbd currently frees oplock_info immediately using kfree(), even
though it is accessed under RCU read-side critical sections in places
like opinfo_get() and proc_show_files().

Since there is no RCU grace period delay between nullifying the pointer
and freeing the memory, a reader can still access oplock_info
structure after it has been freed. This can leads to a use-after-free
especially in opinfo_get() where atomic_inc_not_zero() is called on
already freed memory.

Fix this by switching to deferred freeing using call_rcu().
Comment 1 Alexander B 2026-05-08 17:10:25 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026050831-CVE-2026-43376-e32d@gregkh/T