A use-after-free vulnerability has been resolved in the Linux kernel's DAMON subsystem (CVE-2026-23012). The vulnerability occurs when damon_call() is executed against a non-running DAMON context, potentially leading to memory corruption if the associated object is deallocated and re-accessed. While requiring specific sysfs write permissions and unusual file writes, the issue could be triggered.
In the Linux kernel, the following vulnerability has been resolved:
mm/damon/core: remove call_control in inactive contexts
If damon_call() is executed against a DAMON context that is not running, the function returns error while keeping the damon_call_control object linked to the context's call_controls list. Let's suppose the object is deallocated after the damon_call(), and yet another damon_call() is executed against the same context. The function tries to add the new damon_call_control object to the call_controls list, which still has the pointer to the previous damon_call_control object, which is deallocated. As a result, use-after-free happens.
This can actually be triggered using the DAMON sysfs interface. It is not easily exploitable since it requires the sysfs write permission and making a definitely weird file writes, though. Please refer to the report for more details about the issue reproduction steps.
Fix the issue by making two changes. Firstly, move the final kdamond_call() for cancelling all existing damon_call() requests from terminating DAMON context to be done before the ctx->kdamond reset. This makes any code that sees NULL ctx->kdamond can safely assume the context may not access damon_call() requests anymore. Secondly, let damon_call() to cleanup the damon_call_control objects that were added to the already-terminated DAMON context, before returning the error.