CVE-2026-89748: tracing: Fix retry exhaustion in simple ring buffer reader swap
In the Linux kernel, the following vulnerability has been resolved:
tracing: Fix retry exhaustion in simple ring buffer reader swap
simpleringbufferswapreaderpage() starts with retry set to 8 and post-decrements it only after a failed link replacement. On the final attempt, a successful replacement leaves retry at zero, while a failed replacement leaves it at -1.
The current !retry test reverses both outcomes. It returns an error after a successful final replacement, leaving the link update complete but the reader bookkeeping unfinished. After a failed final replacement, it falls through and updates the head and reader pointers as though the replacement succeeded, which can corrupt the ring.
Treat only a negative counter as exhaustion and return the documented -EBUSY error.
Affected Software
Event History
Frequently Asked Questions
What conditions are required to trigger the corruption scenario?
The issue requires simple_ring_buffer_swap_reader_page() to exhaust its retry sequence for a reader-page link replacement. On the final failed replacement attempt, the function can proceed as if the replacement succeeded and update head and reader pointers, corrupting the ring.
What happens if the final retry succeeds?
A successful link replacement on the final attempt can be incorrectly treated as an error because the retry counter reaches zero. The link update is already complete, but reader bookkeeping is left unfinished.
What is the corrected behavior when retries are exhausted?
Retry exhaustion is now recognized only when the counter becomes negative. In that case, the function returns the documented -EBUSY error instead of updating ring pointers as though the replacement succeeded.