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=-19.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable 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 DD48DC4338F for ; Mon, 2 Aug 2021 14:13:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C08C360E09 for ; Mon, 2 Aug 2021 14:13:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237008AbhHBON5 (ORCPT ); Mon, 2 Aug 2021 10:13:57 -0400 Received: from mail.kernel.org ([198.145.29.99]:48968 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235486AbhHBODO (ORCPT ); Mon, 2 Aug 2021 10:03:14 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 17FC360551; Mon, 2 Aug 2021 13:57:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1627912631; bh=N8TZwqxWv/Mj7Nctq8My+V1fSQrRPpj02DnZFc4aXxY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=2OT+Zku+VdYJKQB3f1ETii3QiinuDb5XuAkjCsERil3p9zOVGqJNEtUyuVR3KQhof 9z0WpwyP/RK9qeKUHdjyUP31oBfYG0PBJBM89iyrqijDgaCc5f0cwyNpPulN8txuVr xpyWSdKEVziSI6Vh3fKVu3qTkg/OtpnGYaQOzuZI= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Tetsuo Handa , Jens Axboe , Sasha Levin Subject: [PATCH 5.13 053/104] loop: reintroduce global lock for safe loop_validate_file() traversal Date: Mon, 2 Aug 2021 15:44:50 +0200 Message-Id: <20210802134345.762851793@linuxfoundation.org> X-Mailer: git-send-email 2.32.0 In-Reply-To: <20210802134344.028226640@linuxfoundation.org> References: <20210802134344.028226640@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Tetsuo Handa [ Upstream commit 3ce6e1f662a910970880188ea7bfd00542bd3934 ] Commit 6cc8e7430801fa23 ("loop: scale loop device by introducing per device lock") re-opened a race window for NULL pointer dereference at loop_validate_file() where commit 310ca162d779efee ("block/loop: Use global lock for ioctl() operation.") has closed. Although we need to guarantee that other loop devices will not change during traversal, we can't take remote "struct loop_device"->lo_mutex inside loop_validate_file() in order to avoid AB-BA deadlock. Therefore, introduce a global lock dedicated for loop_validate_file() which is conditionally taken before local "struct loop_device"->lo_mutex is taken. Signed-off-by: Tetsuo Handa Fixes: 6cc8e7430801fa23 ("loop: scale loop device by introducing per device lock") Signed-off-by: Jens Axboe Signed-off-by: Sasha Levin --- drivers/block/loop.c | 128 ++++++++++++++++++++++++++++++++----------- 1 file changed, 97 insertions(+), 31 deletions(-) diff --git a/drivers/block/loop.c b/drivers/block/loop.c index 8271df125153..e81298b91227 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -86,6 +86,47 @@ static DEFINE_IDR(loop_index_idr); static DEFINE_MUTEX(loop_ctl_mutex); +static DEFINE_MUTEX(loop_validate_mutex); + +/** + * loop_global_lock_killable() - take locks for safe loop_validate_file() test + * + * @lo: struct loop_device + * @global: true if @lo is about to bind another "struct loop_device", false otherwise + * + * Returns 0 on success, -EINTR otherwise. + * + * Since loop_validate_file() traverses on other "struct loop_device" if + * is_loop_device() is true, we need a global lock for serializing concurrent + * loop_configure()/loop_change_fd()/__loop_clr_fd() calls. + */ +static int loop_global_lock_killable(struct loop_device *lo, bool global) +{ + int err; + + if (global) { + err = mutex_lock_killable(&loop_validate_mutex); + if (err) + return err; + } + err = mutex_lock_killable(&lo->lo_mutex); + if (err && global) + mutex_unlock(&loop_validate_mutex); + return err; +} + +/** + * loop_global_unlock() - release locks taken by loop_global_lock_killable() + * + * @lo: struct loop_device + * @global: true if @lo was about to bind another "struct loop_device", false otherwise + */ +static void loop_global_unlock(struct loop_device *lo, bool global) +{ + mutex_unlock(&lo->lo_mutex); + if (global) + mutex_unlock(&loop_validate_mutex); +} static int max_part; static int part_shift; @@ -676,13 +717,15 @@ static int loop_validate_file(struct file *file, struct block_device *bdev) while (is_loop_device(f)) { struct loop_device *l; + lockdep_assert_held(&loop_validate_mutex); if (f->f_mapping->host->i_rdev == bdev->bd_dev) return -EBADF; l = I_BDEV(f->f_mapping->host)->bd_disk->private_data; - if (l->lo_state != Lo_bound) { + if (l->lo_state != Lo_bound) return -EINVAL; - } + /* Order wrt setting lo->lo_backing_file in loop_configure(). */ + rmb(); f = l->lo_backing_file; } if (!S_ISREG(inode->i_mode) && !S_ISBLK(inode->i_mode)) @@ -701,13 +744,18 @@ static int loop_validate_file(struct file *file, struct block_device *bdev) static int loop_change_fd(struct loop_device *lo, struct block_device *bdev, unsigned int arg) { - struct file *file = NULL, *old_file; - int error; - bool partscan; + struct file *file = fget(arg); + struct file *old_file; + int error; + bool partscan; + bool is_loop; - error = mutex_lock_killable(&lo->lo_mutex); + if (!file) + return -EBADF; + is_loop = is_loop_device(file); + error = loop_global_lock_killable(lo, is_loop); if (error) - return error; + goto out_putf; error = -ENXIO; if (lo->lo_state != Lo_bound) goto out_err; @@ -717,11 +765,6 @@ static int loop_change_fd(struct loop_device *lo, struct block_device *bdev, if (!(lo->lo_flags & LO_FLAGS_READ_ONLY)) goto out_err; - error = -EBADF; - file = fget(arg); - if (!file) - goto out_err; - error = loop_validate_file(file, bdev); if (error) goto out_err; @@ -744,7 +787,16 @@ static int loop_change_fd(struct loop_device *lo, struct block_device *bdev, loop_update_dio(lo); blk_mq_unfreeze_queue(lo->lo_queue); partscan = lo->lo_flags & LO_FLAGS_PARTSCAN; - mutex_unlock(&lo->lo_mutex); + loop_global_unlock(lo, is_loop); + + /* + * Flush loop_validate_file() before fput(), for l->lo_backing_file + * might be pointing at old_file which might be the last reference. + */ + if (!is_loop) { + mutex_lock(&loop_validate_mutex); + mutex_unlock(&loop_validate_mutex); + } /* * We must drop file reference outside of lo_mutex as dropping * the file ref can take bd_mutex which creates circular locking @@ -756,9 +808,9 @@ static int loop_change_fd(struct loop_device *lo, struct block_device *bdev, return 0; out_err: - mutex_unlock(&lo->lo_mutex); - if (file) - fput(file); + loop_global_unlock(lo, is_loop); +out_putf: + fput(file); return error; } @@ -1067,22 +1119,22 @@ static int loop_configure(struct loop_device *lo, fmode_t mode, struct block_device *bdev, const struct loop_config *config) { - struct file *file; - struct inode *inode; + struct file *file = fget(config->fd); + struct inode *inode; struct address_space *mapping; - int error; - loff_t size; - bool partscan; - unsigned short bsize; + int error; + loff_t size; + bool partscan; + unsigned short bsize; + bool is_loop; + + if (!file) + return -EBADF; + is_loop = is_loop_device(file); /* This is safe, since we have a reference from open(). */ __module_get(THIS_MODULE); - error = -EBADF; - file = fget(config->fd); - if (!file) - goto out; - /* * If we don't hold exclusive handle for the device, upgrade to it * here to avoid changing device under exclusive owner. @@ -1093,7 +1145,7 @@ static int loop_configure(struct loop_device *lo, fmode_t mode, goto out_putf; } - error = mutex_lock_killable(&lo->lo_mutex); + error = loop_global_lock_killable(lo, is_loop); if (error) goto out_bdev; @@ -1162,6 +1214,9 @@ static int loop_configure(struct loop_device *lo, fmode_t mode, size = get_loop_size(lo, file); loop_set_size(lo, size); + /* Order wrt reading lo_state in loop_validate_file(). */ + wmb(); + lo->lo_state = Lo_bound; if (part_shift) lo->lo_flags |= LO_FLAGS_PARTSCAN; @@ -1173,7 +1228,7 @@ static int loop_configure(struct loop_device *lo, fmode_t mode, * put /dev/loopXX inode. Later in __loop_clr_fd() we bdput(bdev). */ bdgrab(bdev); - mutex_unlock(&lo->lo_mutex); + loop_global_unlock(lo, is_loop); if (partscan) loop_reread_partitions(lo, bdev); if (!(mode & FMODE_EXCL)) @@ -1181,13 +1236,12 @@ static int loop_configure(struct loop_device *lo, fmode_t mode, return 0; out_unlock: - mutex_unlock(&lo->lo_mutex); + loop_global_unlock(lo, is_loop); out_bdev: if (!(mode & FMODE_EXCL)) bd_abort_claiming(bdev, loop_configure); out_putf: fput(file); -out: /* This is safe: open() is still holding a reference. */ module_put(THIS_MODULE); return error; @@ -1202,6 +1256,18 @@ static int __loop_clr_fd(struct loop_device *lo, bool release) bool partscan = false; int lo_number; + /* + * Flush loop_configure() and loop_change_fd(). It is acceptable for + * loop_validate_file() to succeed, for actual clear operation has not + * started yet. + */ + mutex_lock(&loop_validate_mutex); + mutex_unlock(&loop_validate_mutex); + /* + * loop_validate_file() now fails because l->lo_state != Lo_bound + * became visible. + */ + mutex_lock(&lo->lo_mutex); if (WARN_ON_ONCE(lo->lo_state != Lo_rundown)) { err = -ENXIO; -- 2.30.2