CVE-2026-23380tracing: Fix WARN_ON in tracing_buffers_mmap_close

Official description

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 parent's 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 isn't 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 VMA's open callback.

Affected packages & fixed versions

Affected products (as reported)

References

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