From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CB752C35640 for ; Fri, 21 Feb 2020 07:46:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9A48320801 for ; Fri, 21 Feb 2020 07:46:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1582271214; bh=5pz5VyVlGIkxJd83Kh8BCjSgf0Ktw6Y4y60XftuSGmE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=hlw565GQdsYC+/LfUvBLCyLiLcU/lCtn5s2g9M1vwacMLCI69iWrlOU5YJROgc1eZ b4QV4gOhOHsNjewHtYCrWMcTMPaZLrVcKZgEFvDvN7T2t80fJ1/KTj0Y6dl7NlNqBE BmSVGyfQfo2icdePhy+UItnrEKomzxtH/de8sdxc= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728804AbgBUHqx (ORCPT ); Fri, 21 Feb 2020 02:46:53 -0500 Received: from mail.kernel.org ([198.145.29.99]:42458 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728792AbgBUHqs (ORCPT ); Fri, 21 Feb 2020 02:46:48 -0500 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 5A724207FD; Fri, 21 Feb 2020 07:46:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1582271207; bh=5pz5VyVlGIkxJd83Kh8BCjSgf0Ktw6Y4y60XftuSGmE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=ws1GSnl8DssBSy5bi8+XSA1wkjZo/ck9wA5dsXtN1QT6/17a2K5L4EU/B/AhbVHut orvbGMCBlFFoT7rUdCjPw5QWdQhQj7JXkb6oii4mzpFOxC9q6M967zXHOLYWeNPj9Z vDGIceZ0iRDfIrZR6OM74MV1B9JwjPjRRFAQIVeI= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Eric Biggers , Theodore Tso , Sasha Levin Subject: [PATCH 5.5 072/399] ext4: fix deadlock allocating bio_post_read_ctx from mempool Date: Fri, 21 Feb 2020 08:36:37 +0100 Message-Id: <20200221072409.361481698@linuxfoundation.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20200221072402.315346745@linuxfoundation.org> References: <20200221072402.315346745@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Eric Biggers [ Upstream commit 68e45330e341dad2d3a0a3f8ef2ec46a2a0a3bbc ] Without any form of coordination, any case where multiple allocations from the same mempool are needed at a time to make forward progress can deadlock under memory pressure. This is the case for struct bio_post_read_ctx, as one can be allocated to decrypt a Merkle tree page during fsverity_verify_bio(), which itself is running from a post-read callback for a data bio which has its own struct bio_post_read_ctx. Fix this by freeing the first bio_post_read_ctx before calling fsverity_verify_bio(). This works because verity (if enabled) is always the last post-read step. This deadlock can be reproduced by trying to read from an encrypted verity file after reducing NUM_PREALLOC_POST_READ_CTXS to 1 and patching mempool_alloc() to pretend that pool->alloc() always fails. Note that since NUM_PREALLOC_POST_READ_CTXS is actually 128, to actually hit this bug in practice would require reading from lots of encrypted verity files at the same time. But it's theoretically possible, as N available objects isn't enough to guarantee forward progress when > N/2 threads each need 2 objects at a time. Fixes: 22cfe4b48ccb ("ext4: add fs-verity read support") Signed-off-by: Eric Biggers Link: https://lore.kernel.org/r/20191231181222.47684-1-ebiggers@kernel.org Signed-off-by: Theodore Ts'o Signed-off-by: Sasha Levin --- fs/ext4/readpage.c | 17 +++++++++++++++-- 1 file changed, 15 insertions(+), 2 deletions(-) diff --git a/fs/ext4/readpage.c b/fs/ext4/readpage.c index fef7755300c35..410c904cf59b9 100644 --- a/fs/ext4/readpage.c +++ b/fs/ext4/readpage.c @@ -57,6 +57,7 @@ enum bio_post_read_step { STEP_INITIAL = 0, STEP_DECRYPT, STEP_VERITY, + STEP_MAX, }; struct bio_post_read_ctx { @@ -106,10 +107,22 @@ static void verity_work(struct work_struct *work) { struct bio_post_read_ctx *ctx = container_of(work, struct bio_post_read_ctx, work); + struct bio *bio = ctx->bio; - fsverity_verify_bio(ctx->bio); + /* + * fsverity_verify_bio() may call readpages() again, and although verity + * will be disabled for that, decryption may still be needed, causing + * another bio_post_read_ctx to be allocated. So to guarantee that + * mempool_alloc() never deadlocks we must free the current ctx first. + * This is safe because verity is the last post-read step. + */ + BUILD_BUG_ON(STEP_VERITY + 1 != STEP_MAX); + mempool_free(ctx, bio_post_read_ctx_pool); + bio->bi_private = NULL; - bio_post_read_processing(ctx); + fsverity_verify_bio(bio); + + __read_end_io(bio); } static void bio_post_read_processing(struct bio_post_read_ctx *ctx) -- 2.20.1