From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 76BEB33F37A; Sat, 21 Mar 2026 17:54:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774115676; cv=none; b=avIyBwvSwen7++nusbK8MGJz86kdcSXmYCX++72iY1QWFvBvxFPqIR2nBus5UahIZgVyb93clZR4i2lsv9+yPdQ7OfokHzGz48LiGr37EPZALqnqprMzGokOF0T6GyAEcKhy56xlpKmbgbqqBhym40Ys95O4dJmDwdDFqtVQUb0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774115676; c=relaxed/simple; bh=ypF4xKp6F1pbIquY3/unFTj0ZaJ4QsmqDevrapmiqYU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=F9mnHL9vwXoYrPQ1rCnCEPnsy4Wys8YQHPTt3eAKI8QrgTHAZacd0z6e11Vgfw0T/Kn94dJJRLTjlZQcKSxdiIK6xdTp5G/ClK48koTXEA41t7Eqqj8tQAj20xMeqR00ZaDMZQJ3t2dyYxZTXg2lJFWChQBENcEOJadMuQe9cyk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=QPBqAj1U; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="QPBqAj1U" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3E350C2BCB4; Sat, 21 Mar 2026 17:54:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1774115676; bh=ypF4xKp6F1pbIquY3/unFTj0ZaJ4QsmqDevrapmiqYU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=QPBqAj1UYUg3nMWYne8Sya+MKgu4V7EeGKLthl0o51iCB0NAPgs7sQgaXh4Xw8fds 2SU98NaNJ6MzubLEcUwGsVNIrEl9fomH6UIR1GjgcAr0qzkjoKQCVU3SbfxYkY2vZ/ uf2IwjhSs2FLSovNyLMfQUDal9VQijGA5yBmyICBzrzdUi/jhDx/WSjrYUnfLhsc3c D0pPtbGN+xU9+tIGrC28zdpiWLbAFzGViZZ1ZbQB7/Z96r9ZVuZAw9JzvYt0FBTEXj 82ykqjvPVIW7xc+YYHt+LiyuD28YP5oqnjg/0115RkfzVYi01+0926YFH+/QpJMhFr WpIlklGViaYsA== From: SeongJae Park To: Andrew Morton Cc: Josh Law , "# 6 . 17 . x" , SeongJae Park , damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH v3 3/3] mm/damon/sysfs: check contexts->nr in repeat_call_fn Date: Sat, 21 Mar 2026 10:54:26 -0700 Message-ID: <20260321175427.86000-4-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260321175427.86000-1-sj@kernel.org> References: <20260321175427.86000-1-sj@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Josh Law damon_sysfs_repeat_call_fn() calls damon_sysfs_upd_tuned_intervals(), damon_sysfs_upd_schemes_stats(), and damon_sysfs_upd_schemes_effective_quotas() without checking contexts->nr. If nr_contexts is set to 0 via sysfs while DAMON is running, these functions dereference contexts_arr[0] and cause a NULL pointer dereference. Add the missing check. For example, the issue can be reproduced using DAMON sysfs interface and DAMON user-space tool (damo) [1] like below. $ sudo damo start --refresh_interval 1s $ echo 0 | sudo tee \ /sys/kernel/mm/damon/admin/kdamonds/0/contexts/nr_contexts [1] https://github.com/damonitor/damo Link: https://patch.msgid.link/20260320163559.178101-3-objecting@objecting.org Fixes: d809a7c64ba8 ("mm/damon/sysfs: implement refresh_ms file internal work") Cc: # 6.17.x Signed-off-by: Josh Law Reviewed-by: SeongJae Park Signed-off-by: SeongJae Park --- mm/damon/sysfs.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c index ddc30586c0e61..6a44a2f3d8fc9 100644 --- a/mm/damon/sysfs.c +++ b/mm/damon/sysfs.c @@ -1620,9 +1620,12 @@ static int damon_sysfs_repeat_call_fn(void *data) if (!mutex_trylock(&damon_sysfs_lock)) return 0; + if (sysfs_kdamond->contexts->nr != 1) + goto out; damon_sysfs_upd_tuned_intervals(sysfs_kdamond); damon_sysfs_upd_schemes_stats(sysfs_kdamond); damon_sysfs_upd_schemes_effective_quotas(sysfs_kdamond); +out: mutex_unlock(&damon_sysfs_lock); return 0; } -- 2.47.3