From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 E1DB047140C; Tue, 21 Jul 2026 20:16:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784664988; cv=none; b=LVFjKGi1kLR1Wuu0KTVYRXWkJDJGk+IbSlG/LxZ28NvtCBo5aQ9TgGPMIfSnR1Pijq3e8ehKgpskhJ+AgF1UkhAKGWhqI9+2ax3ZawNukFRLgCsrgQfY+CevcVhC8AgvmqvBeOcWroTxPPoIcf/kxtiChPRnIXzeysieT062xwQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784664988; c=relaxed/simple; bh=g4LL5Xb8ZaIid2xd5mKv8R5slvBpSUm02EHGFfmoG3M=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=s65U0C0ij5JskRLqJYvGW+ZEoV5TaQEjMxXcppnuXEelT88wSdUmynjPc+xCI9LDNF3Ole7hsX0qX/tcCtXQIfrovMYGzU6kcZGkploYTD3WGF6xc7LF9oyLqFxzJASCZkvZ/GaA572COPOepTLS4nGmGh+mNlNFznaJtu0F2zM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=R5J6pNlv; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="R5J6pNlv" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 530B01F000E9; Tue, 21 Jul 2026 20:16:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1784664986; bh=v3av2cGmyIZuTJ+HYCotd2jLVGgwD1U5FpjDsFulzE8=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=R5J6pNlvLBLE8Hki1lneFcLUvTrxmywq77LdeGGHaDI9YvfSlKQpAkE6+fP7fyT6L QFS5iaZSHjj6BuKza3vrUoBl5xpt7SBMmO5YoihO/3UBXHo3ElpbyGOr/+g4gDRC9g RYdsZICeypxC6KKYgL8z/yaRNojmiSyMWYcKgss4= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, SeongJae Park , Andrew Morton Subject: [PATCH 6.6 0132/1266] mm/damon/ops-common: handle extreme intervals in damon_hot_score() Date: Tue, 21 Jul 2026 17:09:29 +0200 Message-ID: <20260721152444.758983283@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260721152441.786066624@linuxfoundation.org> References: <20260721152441.786066624@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: SeongJae Park commit 35d4a3cf70a855b50e53189ac2f8463e20a02046 upstream. Fix three issues in damon_hot_score() that comes from wrong handling of extreme (zero or too high) monitoring intervals user setup. When the user sets sampling interval zero, damon_max_nr_accesses(), which is called from damon_hot_score(), causes a divide-by-zero. Needless to say, it is a problem. When the user sets the aggregation interval zero, the function returns zero. It is wrong, since the real maximum nr_acceses in the setup should be one. Worse yet, it can cause another divide-by-zero from its caller, damon_hot_score(), since it uses damon_max_nr_accesses() return value as a denominator. When the user sets the aggregation interval very high, damon_hot_score() could return a value out of [0, DAMOS_MAX_SCORE] range. Since the return value is used as an index to the regions_score_histogram array, which is DAMOS_MAX_SCORE+1 size, it causes out of bounds array access. The issues can be relatively easily reproduced like below. The sysfs write permission is required, though. # ./damo start --damos_action lru_prio --damos_quota_space 100M \ --damos_quota_interval 1s # cd /sys/kernel/mm/damon/admin/kdamonds/0 # echo 0 > contexts/0/monitoring_attrs/intervals/sample_us # echo 0 > contexts/0/monitoring_attrs/intervals/aggr_us # echo commit > state # dmesg [...] [ 131.329762] Oops: divide error: 0000 [#1] SMP NOPTI [...] [ 131.336089] RIP: 0010:damon_hot_score+0x27/0xd0 [...] Fix the divide-by-zero intervals problems by explicitly handling the zero intervals in damon_max_nr_accesses(). Fix the out-of-bound array access by applying [0, DAMOS_MAX_SCORE] bounds before returning from damon_hot_score(). The issue was discovered [1] by Sashiko. Link: https://lore.kernel.org/20260623135834.67189-1-sj@kernel.org Link: https://lore.kernel.org/20260619202459.145010-1-sj@kernel.org [1] Fixes: 198f0f4c58b9 ("mm/damon/vaddr,paddr: support pageout prioritization") Signed-off-by: SeongJae Park Cc: # 5.16.x Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman --- include/linux/damon.h | 8 ++++++-- mm/damon/ops-common.c | 1 + 2 files changed, 7 insertions(+), 2 deletions(-) --- a/include/linux/damon.h +++ b/include/linux/damon.h @@ -669,9 +669,13 @@ static inline bool damon_target_has_pid( static inline unsigned int damon_max_nr_accesses(const struct damon_attrs *attrs) { - /* {aggr,sample}_interval are unsigned long, hence could overflow */ - return min(attrs->aggr_interval / attrs->sample_interval, + unsigned long sample_interval; + unsigned long max_nr_accesses; + + sample_interval = attrs->sample_interval ? : 1; + max_nr_accesses = min(attrs->aggr_interval / sample_interval, (unsigned long)UINT_MAX); + return max_nr_accesses ? : 1; } --- a/mm/damon/ops-common.c +++ b/mm/damon/ops-common.c @@ -107,6 +107,7 @@ int damon_hot_score(struct damon_ctx *c, * Transform it to fit in [0, DAMOS_MAX_SCORE] */ hotness = hotness * DAMOS_MAX_SCORE / DAMON_MAX_SUBSCORE; + hotness = max(min(hotness, DAMOS_MAX_SCORE), 0); return hotness; }