Commit f9132fbc authored by SeongJae Park's avatar SeongJae Park Committed by Andrew Morton
Browse files

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.

Link: https://lkml.kernel.org/r/20251231012315.75835-1-sj@kernel.org


Fixes: 004ded6b ("mm/damon: accept parallel damon_call() requests")
Signed-off-by: default avatarSeongJae Park <sj@kernel.org>
Reported-by: default avatarJaeJoon 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: default avatarAndrew Morton <akpm@linux-foundation.org>
parent e561383a

mm/damon/core.c

+31 −2
Original line number Diff line number Diff line
@@ -1431,6 +1431,35 @@ bool damon_is_running(struct damon_ctx *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, struct damon_call_control *control) 
	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 @@ static int kdamond_fn(void *data) 
	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);