Bug 2404095 (CVE-2025-39976)

Summary: CVE-2025-39976 kernel: futex: Use correct exit on failure from futex_hash_allocate_default()
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Priority: medium    
Version: unspecifiedKeywords: Security
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OS: Linux   
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A flaw was found in the Linux kernel’s futex subsystem: when copy_process() fails in the call to futex_hash_allocate_default(), the code erroneously jumps to an incorrect error-exit label (bad_fork_core_free) that attempts to unlock locks (tasklist_lock and siglock) which were never acquired. This improper error-handling can leave the kernel in an inconsistent locking state, potentially leading to a deadlock or other kernel instability.
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Description OSIDB Bzimport 2025-10-15 08:01:36 UTC 
In the Linux kernel, the following vulnerability has been resolved:

futex: Use correct exit on failure from futex_hash_allocate_default()

copy_process() uses the wrong error exit path from futex_hash_allocate_default().
After exiting from futex_hash_allocate_default(), neither tasklist_lock
nor siglock has been acquired. The exit label bad_fork_core_free unlocks
both of these locks which is wrong.

The next exit label, bad_fork_cancel_cgroup, is the correct exit.
sched_cgroup_fork() did not allocate any resources that need to freed.

Use bad_fork_cancel_cgroup on error exit from futex_hash_allocate_default().
Comment 1 Alexander B 2025-10-16 12:22:12 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2025101558-CVE-2025-39976-59ea@gregkh/T