From: SeongJae Park <sj@kernel.org>
Subject: mm/damon/dbgfs: protect targets destructions with kdamond_lock

DAMON debugfs interface iterates current monitoring targets in
'dbgfs_target_ids_read()' while holding the corresponding 'kdamond_lock'. 
However, it also destructs the monitoring targets in
'dbgfs_before_terminate()' without holding the lock.  This can result in a
use_after_free bug.  This commit avoids the race by protecting the
destruction with the corresponding 'kdamond_lock'.

Link: https://lkml.kernel.org/r/20211221094447.2241-1-sj@kernel.org
Reported-by: Sangwoo Bae <redacted>
Fixes: 4bc05954d007 ("mm/damon: implement a debugfs-based user space interface")
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: <redacted>	[5.15.x]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/damon/dbgfs.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/mm/damon/dbgfs.c~mm-damon-dbgfs-protect-targets-destructions-with-kdamond_lock
+++ a/mm/damon/dbgfs.c

@@ -650,10 +650,12 @@ static void dbgfs_before_terminate(struc
 	if (!targetid_is_pid(ctx))
 		return;
 
+	mutex_lock(&ctx->kdamond_lock);
 	damon_for_each_target_safe(t, next, ctx) {
 		put_pid((struct pid *)t->id);
 		damon_destroy_target(t);
 	}
+	mutex_unlock(&ctx->kdamond_lock);
 }
 
 static struct damon_ctx *dbgfs_new_ctx(void)

_