CVE-2026-46173exit: prevent preemption of oopsing TASK_DEAD task

Official description

In the Linux kernel, the following vulnerability has been resolved: exit: prevent preemption of oopsing TASK_DEAD task When an already-exiting task oopses, make_task_dead() currently calls do_task_dead() with preemption enabled. That is forbidden: do_task_dead() calls __schedule(), which has a comment saying "WARNING: must be called with preemption disabled!". If an oopsing task is preempted in do_task_dead(), between becoming TASK_DEAD and entering the scheduler explicitly, bad things happen: finish_task_switch() assumes that once the scheduler has switched away from a TASK_DEAD task, the task can never run again and its stack is no longer needed; but that assumption apparently doesn't hold if the dead task was preempted (the SM_PREEMPT case). This means that the scheduler ends up repeatedly dropping references on the dead task's stack, which can lead to use-after-free or double-free of the entire task stack; in other words, two tasks can end up running on the same stack, resulting in various kinds of memory corruption. (This does not just affect "recursively oopsing" tasks; it is enough to oops once during task exit, for example in a file_operations::release handler)

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/3d6fb8a7690c23e3213c4b008f64d89a44b98737
• https://git.kernel.org/stable/c/640b4c00fb0e2920327435f6176cbefc3c546165
• https://git.kernel.org/stable/c/7b2800ba5f5f77a8ee7f4cbadb19cf1264597a34
• https://git.kernel.org/stable/c/6f49f94f3b11fe8bff1bf2a054143789e76aaf17
• https://git.kernel.org/stable/c/9756b3db5db6c2f5eccb32dddbd88eb4c54f575e
• https://git.kernel.org/stable/c/c1fa0bb633e4a6b11e83ffc57fa5abe8ebb87891
• https://project-zero.issues.chromium.org/issues/510793286
• https://cert-portal.siemens.com/productcert/html/ssa-019113.html
• https://cert-portal.siemens.com/productcert/html/ssa-457936.html
• https://cert-portal.siemens.com/productcert/html/ssa-784472.html