From nobody Tue Apr 7 14:04:30 2026 Received: from m16.mail.163.com (m16.mail.163.com [220.197.31.3]) (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 B585A45C0B; Thu, 26 Feb 2026 05:05:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=220.197.31.3 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772082322; cv=none; b=GNtPzA3lMvk3J+WELgFvk+YrSonmzEEEoqqLP1YWoPSomk1Uko8qJkaHfGkrismmX6vMMgNa9P9ir8z5FCEAII91n5T6Mym5ByOttLk+MqN6vo4SFmDXwjlO76mwUDZ2IR8ZbbZcW5jPxPJ4D7DtGMsZECAIAXLfBAB/JNHEoIg= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772082322; c=relaxed/simple; bh=kwBh37NANwcXhc2TtJ61Oo+5M4kdUfSb+k5fFH9upZM=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version; b=D9sOys7pzRWjvlt2PMlglGE5RkcuHJXhMiQGrk+51Y21l3ClzCK9OKfbuYgoTszADzZqIitDAgg/6cSQ/epdWquSauczY5fnEo9TGqK2kou+eQ+nrCsQCZXHz8RzWsWcTMhKOFlCh7vURTRjYu0g3A4x5tDhXTuDOklgLz0KMyc= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=163.com; spf=pass smtp.mailfrom=163.com; dkim=pass (1024-bit key) header.d=163.com header.i=@163.com header.b=kksHbjBD; arc=none smtp.client-ip=220.197.31.3 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=163.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=163.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=163.com header.i=@163.com header.b="kksHbjBD" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=163.com; s=s110527; h=From:To:Subject:Date:Message-Id:MIME-Version; bh=nE E27e8uG76RjHLoTbC/alv3uxT1YhabsN0M0uUxzNI=; b=kksHbjBDFwp/dEfPs9 bckbLd4DJZYBQXyzQNQpi3RubpAGxToPN5tftWvp7nrlNwPjQotfpHuDb51xYmAP LVcn/hyHLXBnqH7WVGGqkwg74SJCQUSznEJlo3y0cM7276II+g+EhOwlAXZwBw1o nHfVZz3BgdDqK4sbHDzDvwwSU= Received: from pek-lpg-core6.wrs.com (unknown []) by gzsmtp1 (Coremail) with SMTP id PCgvCgBXrNBV1J9pvRs+Pg--.2127S2; Thu, 26 Feb 2026 13:04:23 +0800 (CST) From: Rahul Sharma To: gregkh@linuxfoundation.org, stable@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Mikulas Patocka , Guangwu Zhang , Sami Tolvanen , Eric Biggers , Rahul Sharma Subject: [PATCH 6.6.y] dm-verity: disable recursive forward error correction Date: Thu, 26 Feb 2026 13:04:18 +0800 Message-Id: <20260226050418.159241-1-black.hawk@163.com> X-Mailer: git-send-email 2.34.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-CM-TRANSID: PCgvCgBXrNBV1J9pvRs+Pg--.2127S2 X-Coremail-Antispam: 1Uf129KBjvJXoWxCFWfKw1DtrW8uF1rZF18Zrb_yoW5GFW8pF Z09a4fCr1rJF4xGryUJ3WUZa45u3srt393GFW3u3Z29a4Fyry8WryUtFW3ZF48Xr97GryY vF4qkFW5Zas5uaDanT9S1TB71UUUUU7qnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDUYxBIdaVFxhVjvjDU0xZFpf9x0pNhFcUUUUUU= X-CM-SenderInfo: 5eoduy4okd4yi6rwjhhfrp/xtbC3heMJmmf1FdMgAAA3a Content-Type: text/plain; charset="utf-8" From: Mikulas Patocka [ Upstream commit d9f3e47d3fae0c101d9094bc956ed24e7a0ee801 ] There are two problems with the recursive correction: 1. It may cause denial-of-service. In fec_read_bufs, there is a loop that has 253 iterations. For each iteration, we may call verity_hash_for_block recursively. There is a limit of 4 nested recursions - that means that there may be at most 253^4 (4 billion) iterations. Red Hat QE team actually created an image that pushes dm-verity to this limit - and this image just makes the udev-worker process get stuck in the 'D' state. 2. It doesn't work. In fec_read_bufs we store data into the variable "fio->bufs", but fio bufs is shared between recursive invocations, if "verity_hash_for_block" invoked correction recursively, it would overwrite partially filled fio->bufs. Signed-off-by: Mikulas Patocka Reported-by: Guangwu Zhang Reviewed-by: Sami Tolvanen Reviewed-by: Eric Biggers [ The context change is due to the commit bdf253d580d7 ("dm-verity: remove support for asynchronous hashes") in v6.18 and the commit 9356fcfe0ac4 ("dm verity: set DM_TARGET_SINGLETON feature flag") in v6.9 which are irrelevant to the logic of this patch. ] Signed-off-by: Rahul Sharma --- drivers/md/dm-verity-fec.c | 4 +--- drivers/md/dm-verity-fec.h | 3 --- 2 files changed, 1 insertion(+), 6 deletions(-) diff --git a/drivers/md/dm-verity-fec.c b/drivers/md/dm-verity-fec.c index 4474352ad3d1..eda646a0d237 100644 --- a/drivers/md/dm-verity-fec.c +++ b/drivers/md/dm-verity-fec.c @@ -439,10 +439,8 @@ int verity_fec_decode(struct dm_verity *v, struct dm_v= erity_io *io, if (!verity_fec_is_enabled(v)) return -EOPNOTSUPP; =20 - if (fio->level >=3D DM_VERITY_FEC_MAX_RECURSION) { - DMWARN_LIMIT("%s: FEC: recursion too deep", v->data_dev->name); + if (fio->level) return -EIO; - } =20 fio->level++; =20 diff --git a/drivers/md/dm-verity-fec.h b/drivers/md/dm-verity-fec.h index 8454070d2824..7a73866f727d 100644 --- a/drivers/md/dm-verity-fec.h +++ b/drivers/md/dm-verity-fec.h @@ -23,9 +23,6 @@ #define DM_VERITY_FEC_BUF_MAX \ (1 << (PAGE_SHIFT - DM_VERITY_FEC_BUF_RS_BITS)) =20 -/* maximum recursion level for verity_fec_decode */ -#define DM_VERITY_FEC_MAX_RECURSION 4 - #define DM_VERITY_OPT_FEC_DEV "use_fec_from_device" #define DM_VERITY_OPT_FEC_BLOCKS "fec_blocks" #define DM_VERITY_OPT_FEC_START "fec_start" --=20 2.34.1