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 E465E3090F5; Thu, 2 Apr 2026 15:23:16 +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=1775143397; cv=none; b=rWuPzByNYfczvlMiSFPo9Kx0U5QOI2+dkOMLFel2x24j9QnEvlJHg1nd6UteI4fcXU9x1VvoKaN8g/6ZTbvzYhXgGPSdrFmM2lIHz7yIuvj7ZsWAQHbWWNjU5G9mzMwq8T/NNWEs93qlq4CYkH2VJ4DfWZz3sSzse6KS0LvKAds= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775143397; c=relaxed/simple; bh=9oVYR4IRaxvDvL0h28oK6fCNi0c0M7sx6EhNv06jmrM=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=G5Zb8m9gcjd3Wh8bROtRT8XcH9YfM4ca1t6wPJJrjh/8pAqlEu0klZTE5C41UgjtD9Ru+XN51daGAvvGc/SvPqzuWSrM/cKyYXlvCoWbhTekpFnRgH7cB7rpV5Iv6lBiMnybTDjlb+/6gTW5ogukhzY9jZ2fhYFfN35jMjCDxO0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=TeY7Uf2q; 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="TeY7Uf2q" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 729BCC116C6; Thu, 2 Apr 2026 15:23:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1775143396; bh=9oVYR4IRaxvDvL0h28oK6fCNi0c0M7sx6EhNv06jmrM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=TeY7Uf2qx87lhQUZWJD1cFm6cVZ0Ib0DKRAsgjQwIUnU82ILe5LlRQN6zj/SGbSTL kOvMfMyIb5u8XnAq8BeVutIpbxMBRPoUzv+aMPpv6n8D0i1U43Oc0Uv01O3qSv8CWo HrJfFo5I2DPalWNuqpGYWgigbw4iGRHQ5K5Uftk8rhxhnvl5BC7aa7+/KrjSZl173q H3AQkVY80Cv08X7DuxmutmA1u1ly1VY1syoQU9SlhnR7j2+wp4qijNSXGMToxNUqRR 1pm0VcYUiL0Yf86qDtaHPEec1cUm4sAKz7ebvqPPsyFAXtVhwFnO8yKc4CcNVkLcLi imiqijvjmHCwQ== From: SeongJae Park To: SeongJae Park Cc: Andrew Morton , damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: (sashiko review) [PATCH v2] mm/damon/stat: deallocate damon_call() failure leaking damon_ctx Date: Thu, 2 Apr 2026 08:23:14 -0700 Message-ID: <20260402152315.75009-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260402134418.74121-1-sj@kernel.org> References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit - stable@, as it seems this is not really need to be shared there. TL; DR: sashiko didn't find any real issue. Forwarding Sashiko review in a reply form with my inline comments, for doing detailed discussions via mails if needed. > # review url: https://sashiko.dev/#/patchset/20260402134418.74121-1-sj@kernel.org > # start of sashiko.dev inline review > commit f956e734cbf12d26893e0ce6fe09667b1ba0ca51 > Author: SeongJae Park > > mm/damon/stat: deallocate damon_call() failure leaking damon_ctx > > This commit attempts to fix a memory leak and avoid a use-after-free > by deferring the deallocation of the damon_ctx object when damon_call() > fails, cleaning it up on the next invocation instead. > > Link: https://lore.kernel.org/20260401012428.86694-1-sj@kernel.org > > > diff --git a/mm/damon/stat.c b/mm/damon/stat.c > > index 30aeb2c207ec3..b1011a7a2f291 100644 > > --- a/mm/damon/stat.c > > +++ b/mm/damon/stat.c > > @@ -245,6 +245,12 @@ static int damon_stat_start(void) > > { > > int err; > > > > + if (damon_stat_context) { > > + if (damon_is_running(damon_stat_context)) > > + return -EAGAIN; > > + damon_destroy_ctx(damon_stat_context); > > + } > > + > > damon_stat_context = damon_stat_build_ctx(); > > [ ... ] > > The commit message notes that deallocating damon_stat_context immediately > after a damon_call() failure leads to a use-after-free if kdamond is still > running. > > However, it appears the immediate deallocation in the error path was > left intact at the end of damon_stat_start(): > > err = damon_call(damon_stat_context, &call_control); > if (err) { > damon_destroy_ctx(damon_stat_context); > damon_stat_context = NULL; > } > return err; > > Since damon_stat_context is still immediately destroyed and set to NULL > when damon_call() fails, does this leave the use-after-free issue > unresolved? > > Additionally, because it is set to NULL, the new deferred cleanup logic > added at the top of the function will evaluate to false on the next > invocation. Should the immediate deallocation block be removed to allow > the new cleanup logic to handle it? Seems sashiko is saying so because sashiko applied the patch on one of mm.git trees that having the v1 of this patch. I asked Andrew to drop the v1, so sashiko's claim shouldn't be a real issue. > > > # end of sashiko.dev inline review > # review url: https://sashiko.dev/#/patchset/20260402134418.74121-1-sj@kernel.org Thanks, SJ [...]