CVE-2026-23380: tracing: Fix WARN_ON in tracing_buffers_mmap_close

Vulnerability summary

CVE-2026-23380 is a medium (CVSS 5.5) Reachable Assertion vulnerability in linux. EPSS estimates a 0.12% chance of exploitation in the next 30 days, higher than 1.7% of scored vulnerabilities.

Timeline

1. 25-03-2026
   PublishedVulnerability first disclosed.
2. 11-05-2026
   Last modifiedVulnerability information updated.

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.

• CWE-617Reachable AssertionThe 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.