CVE-2026-31652mm/damon/stat: deallocate damon_call() failure leaking damon_ctx

Official description

In the Linux kernel, the following vulnerability has been resolved: mm/damon/stat: deallocate damon_call() failure leaking damon_ctx damon_stat_start() always allocates the module's damon_ctx object (damon_stat_context). Meanwhile, if damon_call() in the function fails, the damon_ctx object is not deallocated. Hence, if the damon_call() is failed, and the user writes Y to “enabled” again, the previously allocated damon_ctx object is leaked. This cannot simply be fixed by deallocating the damon_ctx object when damon_call() fails. That's because damon_call() failure doesn't guarantee the kdamond main function, which accesses the damon_ctx object, is completely finished. In other words, if damon_stat_start() deallocates the damon_ctx object after damon_call() failure, the not-yet-terminated kdamond could access the freed memory (use-after-free). Fix the leak while avoiding the use-after-free by keeping returning damon_stat_start() without deallocating the damon_ctx object after damon_call() failure, but deallocating it when the function is invoked again and the kdamond is completely terminated. If the kdamond is not yet terminated, simply return -EAGAIN, as the kdamond will soon be terminated. The issue was discovered [1] by sashiko.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/447f8870b484f6596d7a7130e72bd0a3f1e037bb
• https://git.kernel.org/stable/c/16c92e9bf55fa049ddb5e894dc0623dacd46a620
• https://git.kernel.org/stable/c/4c04c6b47c361612b1d70cec8f7a60b1482d1400