CVE-2025-39877

In the Linux kernel, the following vulnerability has been resolved:

mm/damon/sysfs: fix use-after-free in state_show()

state_show() reads kdamond->damon_ctx without holding damon_sysfs_lock.

This allows a use-after-free race:

CPU 0 CPU 1

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state_show() damon_sysfs_turn_damon_on()

ctx = kdamond->damon_ctx; mutex_lock(&damon_sysfs_lock);

damon_destroy_ctx(kdamond->damon_ctx);

kdamond->damon_ctx = NULL;

mutex_unlock(&damon_sysfs_lock);

damon_is_running(ctx); /* ctx is freed */

mutex_lock(&ctx->kdamond_lock); /* UAF */

(The race can also occur with damon_sysfs_kdamonds_rm_dirs() and

damon_sysfs_kdamond_release(), which free or replace the context under

damon_sysfs_lock.)

Fix by taking damon_sysfs_lock before dereferencing the context, mirroring

the locking used in pid_show().

The bug has existed since state_show() first accessed kdamond->damon_ctx.