From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794167382; b=lxQhcvbrSZBKZNJhzf4QlgjO4JuC57q2Q5pwDzZJrmVsi2V6x/RQpegvnXoOQSA/fBCR ODT6mGiWTWXQcIsXDNjnZ6fI5ZKzu0R+QLwpXe8/os1m+lld5NcsTIm4HKDu9EWzqaDv4 HM5/Xs08qVaL2zzr8I4H97KfJJ5cps4/v9OlcF8tVcAIspyZuTeCJO1edWT77QifmEDij Wp6hYIgQYB/ZpfMxQRwQzHu2Jshkys5Hh95tte99PO30o5v15nXAvQbtuGkJxNs6YjDgz l7UpJTs54Yizl3BxYtCwIzN9bzDP+6nphZStOE9Obkq12JQ13dFmS6m+lUvLpzoINww== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794167382; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:Content-Type: Content-Transfer-Encoding; bh=n2C/GvKXAk+pYFZ4vmrAiRb4WyuL7H3om3GAG5pFiS4=; b=SghITanFuVApxdHTvjw+VqmgeHwK5edzD4jSvX2rvWX6C01o30u524dCrwpJipp42Mat 5Xi/HzncXtirpaKKyG7l45FSWuM/vfTZM+ASnqLJrifnGCMfqc5qP/J8P9Ao6xg8qi/Kt XcBYK40TskWbD/FSHJDErCEJFFXCp62VESEVjPQur75p3/5sldBy9Tb/94wdSL4BApe5N PeU/KXD49rLjZqf7fpjtOR5RI4WRsjzE3WFpFITvzpOiSyrVexwbnvrI0kHIfGNxPVmMF vf5PEm/TKQpePtGkUTX/llu+Z2gBkEiIw61iyByKM/UHEdCAzYBhslrWQfJ0Vloiiuw== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=P58p1Jdp; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2DA6C606A31C for ; Sun, 8 Nov 2026 19:49:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=P58p1Jdp Received: by smtp.kernel.org (Postfix) with ESMTPSA id BD83C1F0089F; Sun, 8 Nov 2026 19:49:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794167382; bh=n2C/GvKXAk+pYFZ4vmrAiRb4WyuL7H3om3GAG5pFiS4=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=P58p1Jdpmst40sGJSxTlkBW03mhyY57bZXMEomEq9m6JwA17nfaqaD0WlzTT8IPVb 33gLkQEBIfk9JSroVmS4GjCMePxSXk2hbYohuaHJmxT+Uy09AMVsxzcDiUQ4FHHTOw hUwVK7QK31hdTL5bIZo0kVqrQ8erbbsuCKAdTuK3kOal5BdQ5bLDwV9bZ10THDJ3Po frW9yPxJW556+oDWKuV8eIDUh9mIUSMsbIvET83aPhLrRsbBZb9Ds6mdCPy1Qq/GtK Kklx0S1K8Rn0TIMugKLJhOdRcKpXoXMVbPqa5dEwTd3m6GMOqloTQg1TeNmASQT6Ry 0nm6yNER8AGbQ== From: SJ Park To: sashiko-bot@kernel.org Cc: SJ Park , "Andrew Morton" , "Brendan Higgins" , "David Gow" , "Usama Arif" , damon@lists.linux.dev, linux-mm@kvack.org Subject: Re: [PATCH 6.18.y 3/5] mm/damon/sysfs-schemes: read sysfs_filter->sz_range only once Date: Sun, 8 Nov 2026 11:49:33 -0800 Message-ID: <20261108194935.115238-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: References: X-Mailing-List: damon@lists.linux.dev List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On Sun, 08 Nov 2026 19:30:36 +0000 sashiko-bot@kernel.org wrote: > Thank you for your contribution! Sashiko AI review found no new issues > in this patch, but noticed 1 related pre-existing issue it does not > introduce: > - [High] mm/damon/sysfs: TOCTOU race in damos_sysfs_add_quota_score() > [1] > -- > > commit 244e62bfada7cc56b0025da40ea03dad6d9c6420 > Author: SJ Park > > mm/damon/sysfs-schemes: read sysfs_filter->sz_range only once > > This commit copies sysfs_filter->sz_range into filter->sz_range before > validating it in damon_sysfs_add_scheme_filters() so that a concurrent > sysfs update cannot pass an unvalidated size range to the core layer. > > Link: https://lore.kernel.org/20260914142327.92510-3-sj@kernel.org > > > diff --git a/mm/damon/sysfs-schemes.c b/mm/damon/sysfs-schemes.c > > index 37e0a8bef4b1f..0f945ef043709 100644 > > --- a/mm/damon/sysfs-schemes.c > > +++ b/mm/damon/sysfs-schemes.c > > @@ -2493,12 +2493,11 @@ static int damon_sysfs_add_scheme_filters(struct damos *scheme, > > } else if (filter->type == DAMOS_FILTER_TYPE_TARGET) { > > filter->target_idx = sysfs_filter->target_idx; > > } else if (filter->type == DAMOS_FILTER_TYPE_HUGEPAGE_SIZE) { > > - if (sysfs_filter->sz_range.min > > > - sysfs_filter->sz_range.max) { > > + filter->sz_range = sysfs_filter->sz_range; > > + if (filter->sz_range.min > filter->sz_range.max) { > > damos_destroy_filter(filter); > > return -EINVAL; > > } > > - filter->sz_range = sysfs_filter->sz_range; > > } > > > > damos_add_filter(scheme, filter); > > [Severity: High] > This problem wasn't introduced by this patch, but can > damos_sysfs_add_quota_score() just below hit a similar double-read race on > sysfs_goal->target_value [1]? > > mm/damon/sysfs-schemes.c:damos_sysfs_add_quota_score() { > ... > if (!sysfs_goal->target_value) > continue; > > goal = damos_new_quota_goal(sysfs_goal->metric, > sysfs_goal->target_value); > ... > } > > target_value_store() updates sysfs_goal->target_value without holding > damon_sysfs_lock: > > CPU0 CPU1 > damos_sysfs_add_quota_score() > if (!sysfs_goal->target_value) > target_value_store() > kstrtoul(..., &goal->target_value) > damos_new_quota_goal(..., > sysfs_goal->target_value) > ... > damos_quota_score() > mult_frac(..., > goal->target_value) <-- divide-by-zero > > If a concurrent write sets sysfs_goal->target_value to 0 between the check > and the second read, damos_new_quota_goal() creates a goal with a zero > target_value, which later causes a divide-by-zero in damos_quota_score(). > sysfs_goal->metric is also read twice in damos_sysfs_add_quota_score(), so > a concurrent metric_store() between damos_new_quota_goal() and the switch > can leave goal->nid or goal->current_value uninitialized. No. damon_sysfs_valid_start_ctx() [1] avoids the divide-by-zero. [1] https://lore.kernel.org/all/20260903010722.94244-2-sj@kernel.org/ > > [1] https://sashiko.dev/#/bug/linux-7f814c9a-986f-4103-a55a-ef9537dcf62b > > -- > Sashiko AI review ยท https://sashiko.dev/#/patchset/20261108192221.114362-1-sj@kernel.org?part=3 > Thanks, SJ