From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 30535109446F for ; Sat, 21 Mar 2026 17:54:46 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 47F986B00EF; Sat, 21 Mar 2026 13:54:39 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 403876B00F2; Sat, 21 Mar 2026 13:54:39 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 2D1186B00F0; Sat, 21 Mar 2026 13:54:39 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id E88266B00EF for ; Sat, 21 Mar 2026 13:54:38 -0400 (EDT) Received: from smtpin16.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay05.hostedemail.com (Postfix) with ESMTP id AE283551FE for ; Sat, 21 Mar 2026 17:54:38 +0000 (UTC) X-FDA: 84570820236.16.990ACF0 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf07.hostedemail.com (Postfix) with ESMTP id 1609E4000B for ; Sat, 21 Mar 2026 17:54:36 +0000 (UTC) Authentication-Results: imf07.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=JCIHzKeX; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf07.hostedemail.com: domain of sj@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=sj@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1774115677; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=HOnYaB2tAwTK08iBhyNP0vgp16q57l/Gx40280DuIm8=; b=7S3K4tEFh0QYfmxt+isym4AxDqf1o+im9iCyHGk1TKIm4xdiFYwiQ/4xKT6VPvp7ShHgec VveeYLZb3HrwNWnj6R+/DtjQgtYWzcy40Tp6/3HXVx7b2XgREtMiUvaOks4HbLEi8obCHc tVdNmJyIgV9kXfxE9mlmsGLxakDW7Vs= ARC-Authentication-Results: i=1; imf07.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=JCIHzKeX; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf07.hostedemail.com: domain of sj@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=sj@kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1774115677; a=rsa-sha256; cv=none; b=q+METUvKzrllqk34+Jmmi5hQKDXLKnkthTRtr8FWxbLqxOeShMI8SMD1V9rQCIZMlWiu6U H2AjxvqMgr87V70bpGf9XLGehEr6gQSo2fpZb/pVikYgc9QSqZ2ZK/SeGIlmAho5Hj2Egh n+Rn3XiRhlkhZWCugB3LnhTX75T0gi4= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id 3EF344457A; Sat, 21 Mar 2026 17:54:36 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0406CC2BCB1; Sat, 21 Mar 2026 17:54:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1774115676; bh=ozaZfolHMPA3TCsXC61RgAmpZFbdf9+Z14L9tHNxdsM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=JCIHzKeX5pvZa/pwEj3y0EPD5StACRN04orUN65Kdv1WXpLao9Dujx/qWb/mXU4+C RVus4wCtn5m7UE7RqBn42VtY5j9UsdYWu1juthqS5tAfl5+UpXVYz7n1nn0uMaqh2L d0G5RwzGCzVI+SAvT6EVzdyKpu7150vdTBnFLBktJ8ZJnh/KP+hZa/jy/ocj33DodK MfA3LgZbo0y5KgbHsEJFWJQZJtbssPudiDvd0u58tn5HsXH1rP+itsnU9dCrSLUdyq tocW0aUsuhxVLw8eshlOWJLk3oKuRZx80ObGUz5H61jxy340nZPrKjLz7h3MRPlEeU qZGrGlBzTQx8g== From: SeongJae Park To: Andrew Morton Cc: Josh Law , "# 5 . 18 . x" , SeongJae Park , damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH v3 2/3] mm/damon/sysfs: check contexts->nr before accessing contexts_arr[0] Date: Sat, 21 Mar 2026 10:54:25 -0700 Message-ID: <20260321175427.86000-3-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> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 1609E4000B X-Stat-Signature: y4xcojpneh5jkaeg53fk7xpjtiauhpm9 X-Rspam-User: X-HE-Tag: 1774115676-187298 X-HE-Meta: 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 NyiJbtGe EGoMEbRbI0tbX81JK8gP16dIFEe+4u2Hu9zqDysFsktXi3SDcM07J82J2SvvBT+PFvxbY6x9uq+SH1gk7yv63dvkB2PjNi3F/KrFFQvHT8Q2K019mXBahV9nDpDU2m6dyPmFlBB7mKu75CyVmA0OILkvfKT4u5rnMsiSA18jpjw7mzmDge/TmkMNdKa3FAo704z/L0g7i5/jlzmKV16mdqVCKA11VUWud7H7kBSKskrijPgjv9qVtCkAmoCdVQptUskyUYp9YeiBDSYPqXsLS989JOOQBlngTnUcDz+9BCmNu8SOuekfKnnWpLGNZ9NT1nuYx9Q/q3+qa64CVKwoEM6LpvA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: From: Josh Law Multiple sysfs command paths dereference contexts_arr[0] without first verifying that kdamond->contexts->nr == 1. A user can set nr_contexts to 0 via sysfs while DAMON is running, causing NULL pointer dereferences. In more detail, the issue can be triggered by privileged users like below. First, start DAMON and make contexts directory empty (kdamond->contexts->nr == 0). # damo start # cd /sys/kernel/mm/damon/admin/kdamonds/0 # echo 0 > contexts/nr_contexts Then, each of below commands will cause the NULL pointer dereference. # echo update_schemes_stats > state # echo update_schemes_tried_regions > state # echo update_schemes_tried_bytes > state # echo update_schemes_effective_quotas > state # echo update_tuned_intervals > state Guard all commands (except OFF) at the entry point of damon_sysfs_handle_cmd(). Fixes: 0ac32b8affb5 ("mm/damon/sysfs: support DAMOS stats") Cc: # 5.18.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 b573b9d607848..ddc30586c0e61 100644 --- a/mm/damon/sysfs.c +++ b/mm/damon/sysfs.c @@ -1749,6 +1749,9 @@ static int damon_sysfs_update_schemes_tried_regions( static int damon_sysfs_handle_cmd(enum damon_sysfs_cmd cmd, struct damon_sysfs_kdamond *kdamond) { + if (cmd != DAMON_SYSFS_CMD_OFF && kdamond->contexts->nr != 1) + return -EINVAL; + switch (cmd) { case DAMON_SYSFS_CMD_ON: return damon_sysfs_turn_damon_on(kdamond); -- 2.47.3