The patch titled Subject: mm/damon/core: remove call_control in inactive contexts has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-damon-core-remove-call_control-in-inactive-contexts.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: SeongJae Park sj@kernel.org Subject: mm/damon/core: remove call_control in inactive contexts Date: Tue, 30 Dec 2025 17:23:13 -0800

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.

Link: https://lkml.kernel.org/r/20251231012315.75835-1-sj@kernel.org Fixes: 004ded6bee11 ("mm/damon: accept parallel damon_call() requests") Signed-off-by: SeongJae Park sj@kernel.org Reported-by: JaeJoon Jung rgbi3307@gmail.com Closes: https://lore.kernel.org/20251224094401.20384-1-rgbi3307@gmail.com Cc: stable@vger.kernel.org # 6.17.x Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/damon/core.c | 33 +++++++++++++++++++++++++++++++-- 1 file changed, 31 insertions(+), 2 deletions(-)

--- a/mm/damon/core.c~mm-damon-core-remove-call_control-in-inactive-contexts +++ a/mm/damon/core.c @@ -1431,6 +1431,35 @@ bool damon_is_running(struct damon_ctx * return running; }

+/* + * damon_call_handle_inactive_ctx() - handle DAMON call request that added to + * an inactive context. + * @ctx: The inactive DAMON context. + * @control: Control variable of the call request. + * + * This function is called in a case that @control is added to @ctx but @ctx is + * not running (inactive). See if @ctx handled @control or not, and cleanup + * @control if it was not handled. + * + * Returns 0 if @control was handled by @ctx, negative error code otherwise. + */ +static int damon_call_handle_inactive_ctx( + struct damon_ctx *ctx, struct damon_call_control *control) +{ + struct damon_call_control *c; + + mutex_lock(&ctx->call_controls_lock); + list_for_each_entry(c, &ctx->call_controls, list) { + if (c == control) { + list_del(&control->list); + mutex_unlock(&ctx->call_controls_lock); + return -EINVAL; + } + } + mutex_unlock(&ctx->call_controls_lock); + return 0; +} + /** * damon_call() - Invoke a given function on DAMON worker thread (kdamond). * @ctx: DAMON context to call the function for. @@ -1461,7 +1490,7 @@ int damon_call(struct damon_ctx *ctx, st list_add_tail(&control->list, &ctx->call_controls); mutex_unlock(&ctx->call_controls_lock); if (!damon_is_running(ctx)) - return -EINVAL; + return damon_call_handle_inactive_ctx(ctx, control); if (control->repeat) return 0; wait_for_completion(&control->completion); @@ -2755,13 +2784,13 @@ done: if (ctx->ops.cleanup) ctx->ops.cleanup(ctx); kfree(ctx->regions_score_histogram); + kdamond_call(ctx, true);

pr_debug("kdamond (%d) finishes\n", current->pid); mutex_lock(&ctx->kdamond_lock); ctx->kdamond = NULL; mutex_unlock(&ctx->kdamond_lock);

- kdamond_call(ctx, true); damos_walk_cancel(ctx);

mutex_lock(&damon_lock); _

Patches currently in -mm which might be from sj@kernel.org are

mm-damon-core-remove-call_control-in-inactive-contexts.patch mm-damon-core-introduce-nr_snapshots-damos-stat.patch mm-damon-sysfs-schemes-introduce-nr_snapshots-damos-stat-file.patch docs-mm-damon-design-update-for-nr_snapshots-damos-stat.patch docs-admin-guide-mm-damon-usage-update-for-nr_snapshots-damos-stat.patch docs-abi-damon-update-for-nr_snapshots-damos-stat.patch mm-damon-update-damos-kerneldoc-for-stat-field.patch mm-damon-core-implement-max_nr_snapshots.patch mm-damon-sysfs-schemes-implement-max_nr_snapshots-file.patch docs-mm-damon-design-update-for-max_nr_snapshots.patch docs-admin-guide-mm-damon-usage-update-for-max_nr_snapshots.patch docs-abi-damon-update-for-max_nr_snapshots.patch mm-damon-core-add-trace-point-for-damos-stat-per-apply-interval.patch mm-damon-sysfs-cleanup-intervals-subdirs-on-attrs-dir-setup-failure.patch mm-damon-sysfs-cleanup-attrs-subdirs-on-context-dir-setup-failure.patch mm-damon-sysfs-scheme-cleanup-quotas-subdirs-on-scheme-dir-setup-failure.patch mm-damon-sysfs-scheme-cleanup-access_pattern-subdirs-on-scheme-dir-setup-failure.patch mm-damon-tests-core-kunit-add-test-cases-for-multiple-regions-in-damon_test_split_regions_of-fix.patch