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 E42A336F42C; Tue, 31 Mar 2026 05:30:01 +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=1774935002; cv=none; b=EIpm0EK4A+IAlDsugAFwELrCCxueW1Bd/Fi/soN5UAxypE0zV7JWEp3XK4sX/SAxMX6715BWs+DycB+pAVongVwDU+GJR6xW/58wb98fJ1bLt8qXvKLWVDh2HkEXmACcf2ldUPvw5QuzzO2LHp2L7VEPTh0o+lWxUt1B0jE34AA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774935002; c=relaxed/simple; bh=KJHZYM+ehxHHJBXpt1MD5YGvWlY42uOJ4mL62puB1cU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=QB1vPmKToSPBpByDiOGrwSAcDRptyuVAxAUOm74OWZRleROjUH4g5s3Bn060rsORzyKsT2A0DJ4P1t9MnpHbNhvFA3GBclDSNLEie4zB/LBAohudF2dxzuEI0aAx5+V5/0dKVTBEO6AeCi+zlIsAWyZXX8tF8RiA38ldAiNQqsA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Yy5V62C/; 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="Yy5V62C/" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5AC61C19423; Tue, 31 Mar 2026 05:30:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1774935001; bh=KJHZYM+ehxHHJBXpt1MD5YGvWlY42uOJ4mL62puB1cU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Yy5V62C/mjfsvi85AOblFk+jrZ2o8/Nch95sGlK/qYdu1aC0jPN/p8bF72x9dtt2R DgR8V8Ctcr8tjbf78YPkDKlCeFq3PGNwbLhssyyx6G+yYYhF5QIjB9qyIF/iz4Li4R bzeFCCFclnYEXOtbhTiVIipcfgFyMkwU6YJPeHEhZnVz05VlpoJRMQ9QWktqILkpBg tjBN+VGUGtYwN57r3T72P9m/HuClNesIuhgaJ8QNLSDIJvXbjqmwAZu9q344u94Ya2 3KUaAdhHGrXpiJS61lOMWsCAfASkF5cPL28ryeKXzhINl9TFVs6xwgOCAa8gtIBlCP gsfwAdtWvMpcA== From: SeongJae Park To: stable@vger.kernel.org Cc: damon@lists.linux.dev, Josh Law , SeongJae Park , Andrew Morton Subject: [PATCH 6.1.y] mm/damon/sysfs: check contexts->nr before accessing contexts_arr[0] Date: Mon, 30 Mar 2026 22:29:59 -0700 Message-ID: <20260331052959.77831-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <2026033040-expedited-twentieth-454a@gregkh> References: <2026033040-expedited-twentieth-454a@gregkh> 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 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(). Link: https://lkml.kernel.org/r/20260321175427.86000-3-sj@kernel.org Fixes: 0ac32b8affb5 ("mm/damon/sysfs: support DAMOS stats") Signed-off-by: Josh Law Reviewed-by: SeongJae Park Signed-off-by: SeongJae Park Cc: [5.18+] Signed-off-by: Andrew Morton (cherry picked from commit 1bfe9fb5ed2667fb075682408b776b5273162615) 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 a5a1e90e53e7..bdcf895a29a7 100644 --- a/mm/damon/sysfs.c +++ b/mm/damon/sysfs.c @@ -2576,6 +2576,9 @@ static int damon_sysfs_handle_cmd(enum damon_sysfs_cmd cmd, { bool need_wait = true; + if (cmd != DAMON_SYSFS_CMD_OFF && kdamond->contexts->nr != 1) + return -EINVAL; + /* Handle commands that doesn't access DAMON context-internal data */ switch (cmd) { case DAMON_SYSFS_CMD_ON: -- 2.47.3