CVE-2026-23380

In the Linux kernel, the following vulnerability has been resolved:

tracing: Fix WARN_ON in tracing_buffers_mmap_close

When a process forks, the child process copies the parents VMAs but the user_mapped reference count is not incremented. As a result, when both the parent and child processes exit, tracing_buffers_mmap_close() is called twice. On the second call, user_mapped is already 0, causing the function to return -ENODEV and triggering a WARN_ON.

Normally, this isnt an issue as the memory is mapped with VM_DONTCOPY set. But this is only a hint, and the application can call madvise(MADVISE_DOFORK) which resets the VM_DONTCOPY flag. When the application does that, it can trigger this issue on fork.

Fix it by incrementing the user_mapped reference count without re-mapping the pages in the VMAs open callback.

Weakness

The product contains an assert() or similar statement that can be triggered by an attacker, which leads to an application exit or other behavior that is more severe than necessary.

Affected Software

Extended Description

While assertion is good for catching logic errors and reducing the chances of reaching more serious vulnerability conditions, it can still lead to a denial of service. For example, if a server handles multiple simultaneous connections, and an assert() occurs in one single connection that causes all other connections to be dropped, this is a reachable assertion that leads to a denial of service.

Potential Mitigations

References

• https://git.kernel.org/stable/c/91f3e8d84c89918769e71393f839c9fefadc2580
• https://git.kernel.org/stable/c/b0f269ba6fefe9e3cb9feedcf78fcd0b633800c0
• https://git.kernel.org/stable/c/cdd96641b64297a2db42676f051362b76280a58b
• https://git.kernel.org/stable/c/e39bb9e02b68942f8e9359d2a3efe7d37ae6be0e