linux-kernel - [PATCH] mm/damon/core: make damon_start() waits until kdamond

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [day] [month] [year] [list]

Date:   Fri,  8 Dec 2023 17:50:18 +0000
From:   SeongJae Park <sj@...nel.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     SeongJae Park <sj@...nel.org>, Changbin Du <changbin.du@...el.com>,
        Jakub Acs <acsjakub@...zon.de>, damon@...ts.linux.dev,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: [PATCH] mm/damon/core: make damon_start() waits until kdamond_fn() starts

The cleanup tasks of kdamond threads including reset of corresponding
DAMON context's ->kdamond field and decrease of global nr_running_ctxs
counter is supposed to be executed by kdamond_fn().  However, commit
0f91d13366a4 ("mm/damon: simplify stop mechanism") made neither
damon_start() nor damon_stop() ensure the corresponding kdamond has
started the execution of kdamond_fn().

As a result, the cleanup can be skipped if damon_stop() is called fast
enough after the previous damon_start().  Especially the skipped reset
of ->kdamond could cause a use-after-free.

Fix it by waiting for start of kdamond_fn() execution from
damon_start().

Fixes: 0f91d13366a4 ("mm/damon: simplify stop mechanism")
Reported-by: Jakub Acs <acsjakub@...zon.de>
Cc: <stable@...r.kernel.org> # 5.15.x
Signed-off-by: SeongJae Park <sj@...nel.org>
---
Note that the report has not publicly made, so this patch doesn't have a
Closes: tag.

 include/linux/damon.h | 2 ++
 mm/damon/core.c       | 6 ++++++
 2 files changed, 8 insertions(+)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index aa34ab433bc5..12510d8c51c6 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -579,6 +579,8 @@ struct damon_ctx {
 	 * update
 	 */
 	unsigned long next_ops_update_sis;
+	/* for waiting until the execution of the kdamond_fn is started */
+	struct completion kdamond_started;
 
 /* public: */
 	struct task_struct *kdamond;
diff --git a/mm/damon/core.c b/mm/damon/core.c
index f91715a58dc7..2c0cc65d041e 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -445,6 +445,8 @@ struct damon_ctx *damon_new_ctx(void)
 	if (!ctx)
 		return NULL;
 
+	init_completion(&ctx->kdamond_started);
+
 	ctx->attrs.sample_interval = 5 * 1000;
 	ctx->attrs.aggr_interval = 100 * 1000;
 	ctx->attrs.ops_update_interval = 60 * 1000 * 1000;
@@ -668,11 +670,14 @@ static int __damon_start(struct damon_ctx *ctx)
 	mutex_lock(&ctx->kdamond_lock);
 	if (!ctx->kdamond) {
 		err = 0;
+		reinit_completion(&ctx->kdamond_started);
 		ctx->kdamond = kthread_run(kdamond_fn, ctx, "kdamond.%d",
 				nr_running_ctxs);
 		if (IS_ERR(ctx->kdamond)) {
 			err = PTR_ERR(ctx->kdamond);
 			ctx->kdamond = NULL;
+		} else {
+			wait_for_completion(&ctx->kdamond_started);
 		}
 	}
 	mutex_unlock(&ctx->kdamond_lock);
@@ -1483,6 +1488,7 @@ static int kdamond_fn(void *data)
 
 	pr_debug("kdamond (%d) starts\n", current->pid);
 
+	complete(&ctx->kdamond_started);
 	kdamond_init_intervals_sis(ctx);
 
 	if (ctx->ops.init)
-- 
2.34.1