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 <sangwoob@amazon.com>
Fixes: 4bc05954d007 ("mm/damon: implement a debugfs-based user space interface")
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: <stable@vger.kernel.org>	[5.15.x]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/damon/dbgfs.c b/mm/damon/dbgfs.c
index 1efac0022e9a46b2a94ba0329bbe157a33fc83d5..4fbd729edc9e7cd297bb05579493ace53e7f569c 100644 (file)
--- a/mm/damon/dbgfs.c
+++ b/mm/damon/dbgfs.c
@@ -650,10 +650,12 @@ static void dbgfs_before_terminate(struct damon_ctx *ctx)
        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)