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 4CDA0175A92; Thu, 2 Apr 2026 04:59:30 +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=1775105970; cv=none; b=BMP0vJmdRmfhujQFQekbzksK46Y160ulgMMiMarZyspyXL9ng7coG2CJufDk3mgl9caVPfDEvsmAskqxDmX7J+0T9SLoAg7Aq/TC0TCSGq1Tr6FET00pMl0sQ25fNUJXzUncztA/yrOiK2Ipq9xuw6APQRDZGmmi3sWDzbSV16w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775105970; c=relaxed/simple; bh=6b8L0fz6vN2/1FdAdwuuqgyRC2q1kGbwXl4DDedgmOI=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version:Content-Type; b=YEdCLCc77AFILfAfwPlAExJcd3SHPe1WihMOonyjHQCn0AcvQUB/Q01ipCnYUB+t94H4HvPxSg9Lf/IZVJjMD6/6Ip+omvH1fljjW2yGnIcjg5lOcT1L499Xbx1PJda0C11Ha1VpMviu5bx9LAL0VnWGMz0XXAfKcd9nAsNtJyw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=GQNSxGvJ; 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="GQNSxGvJ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A3824C19423; Thu, 2 Apr 2026 04:59:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1775105969; bh=6b8L0fz6vN2/1FdAdwuuqgyRC2q1kGbwXl4DDedgmOI=; h=From:To:Cc:Subject:Date:From; b=GQNSxGvJXNxyEJ8v1iJtxRdhpFpT1UYFKJ2nnOYJl+ulwa6klYQoB6lX5VLEG+JCF 4iGHNsT1VIi/PO83r/d2jEJjs9so9qxp1loeCIPhgDZ5Fcn6FOF4M6Zt5uBSKj5DX2 LDdEXkgxEY7Flg/ZYxqN41UwCVFiOY4w++btd031t1Odw9qIlxV/TP4wzgSAk3Wa50 fVuq9QOr3nyRik1CAnheYNYAHjU3JkiE5g5MtwalsHw0d/Y91Dcf2pwdiCRxmnYdSb X72Eaifh5mxpADuWsJOClBuFA1CTpt6uBcyCaDLYL5sjLBPpatQko5uXVL9ONmHQRp 75aHoyYgf7eEQ== From: SeongJae Park To: Cc: SeongJae Park , "# 6 . 17 . x" , Andrew Morton , damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [RFC PATCH] mm/damon/stat: deallocate damon_call() failure leaking damon_ctx Date: Wed, 1 Apr 2026 21:59:26 -0700 Message-ID: <20260402045928.71170-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit damon_stat_start() always allocates the module's damon_ctx object (damon_stat_context). Meanwhile, if damon_call() in the function fails, the damon_ctx object is not deallocated. Hence, if the damon_call() is failed, and the user writes Y to “enabled” again, the previously allocated damon_ctx object is leaked. This cannot simply be fixed by deallocating the damon_ctx object when damon_call() fails. That's because damon_call() failure doesn't guarantee the kdamond main function, which accesses the damon_ctx object, is completely finished. In other words, if damon_stat_start() deallocates the damon_ctx object after damon_call() failure, the not-yet-terminated kdamond could access the freed memory (use-after-free). Fix the leak while avoiding the use-after-free by keeping returning damon_stat_start() without deallocating the damon_ctx object after damon_call() failure, but deallocating it when the function is invoked again and the kdamond is completely terminated. If the kdamond is not yet terminated, simply return -EAGAIN, as the kdamond will soon be terminated. The issue was discovered [1] by sashiko. [1] https://lore.kernel.org/20260401012428.86694-1-sj@kernel.org Fixes: 405f61996d9d ("mm/damon/stat: use damon_call() repeat mode instead of damon_callback") Cc: # 6.17.x Signed-off-by: SeongJae Park --- Changes from v1 (https://lore.kernel.org/20260402010457.66860-1-sj@kernel.org) - Avoid use-after-free. - Add RFC tag. mm/damon/stat.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/mm/damon/stat.c b/mm/damon/stat.c index 5a742fc157e4..99ba346f9e32 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(); if (!damon_stat_context) return -ENOMEM; @@ -264,6 +270,7 @@ static void damon_stat_stop(void) { damon_stop(&damon_stat_context, 1); damon_destroy_ctx(damon_stat_context); + damon_stat_context = NULL; } static int damon_stat_enabled_store( base-commit: 4fd04f750d79667937931314ed64c9d79b0d82ef -- 2.47.3