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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1D8AEC433FE for ; Wed, 19 Oct 2022 13:48:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233635AbiJSNse (ORCPT ); Wed, 19 Oct 2022 09:48:34 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42572 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233492AbiJSNrT (ORCPT ); Wed, 19 Oct 2022 09:47:19 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2F85C172503; Wed, 19 Oct 2022 06:32:30 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 9DE8DB82435; Wed, 19 Oct 2022 08:58:22 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1897CC433C1; Wed, 19 Oct 2022 08:58:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1666169901; bh=436goTtGP7cjA/vtXH88LMq5NRFPoKFfaJ/IZ4MBkUI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=be11nvRYUcNMJPsB9UbrpBGdmgfmxhCb441+vyBSU9vxoM2gIK8TYuZpa9uQoEYO2 wSxG0oeukW9iFp8X1TILnYRLDJoUpX/JgJySYZ24cHj+SOmLhxVnvd8pSsM22xlyvT ZQ2Nh0jStRNB4tmeimFdkI1XCGolbFFs4dLddFW8= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Jeff Layton , Amir Goldstein , Al Viro , Sasha Levin Subject: [PATCH 6.0 418/862] locks: fix TOCTOU race when granting write lease Date: Wed, 19 Oct 2022 10:28:25 +0200 Message-Id: <20221019083308.434615073@linuxfoundation.org> X-Mailer: git-send-email 2.38.0 In-Reply-To: <20221019083249.951566199@linuxfoundation.org> References: <20221019083249.951566199@linuxfoundation.org> User-Agent: quilt/0.67 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Amir Goldstein [ Upstream commit d6da19c9cace63290ccfccb1fc35151ffefc0bec ] Thread A trying to acquire a write lease checks the value of i_readcount and i_writecount in check_conflicting_open() to verify that its own fd is the only fd referencing the file. Thread B trying to open the file for read will call break_lease() in do_dentry_open() before incrementing i_readcount, which leaves a small window where thread A can acquire the write lease and then thread B completes the open of the file for read without breaking the write lease that was acquired by thread A. Fix this race by incrementing i_readcount before checking for existing leases, same as the case with i_writecount. Use a helper put_file_access() to decrement i_readcount or i_writecount in do_dentry_open() and __fput(). Fixes: 387e3746d01c ("locks: eliminate false positive conflicts for write lease") Reviewed-by: Jeff Layton Signed-off-by: Amir Goldstein Signed-off-by: Al Viro Signed-off-by: Sasha Levin --- fs/file_table.c | 7 +------ fs/internal.h | 10 ++++++++++ fs/open.c | 11 ++++------- 3 files changed, 15 insertions(+), 13 deletions(-) diff --git a/fs/file_table.c b/fs/file_table.c index 99c6796c9f28..dd88701e54a9 100644 --- a/fs/file_table.c +++ b/fs/file_table.c @@ -324,12 +324,7 @@ static void __fput(struct file *file) } fops_put(file->f_op); put_pid(file->f_owner.pid); - if ((mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ) - i_readcount_dec(inode); - if (mode & FMODE_WRITER) { - put_write_access(inode); - __mnt_drop_write(mnt); - } + put_file_access(file); dput(dentry); if (unlikely(mode & FMODE_NEED_UNMOUNT)) dissolve_on_fput(mnt); diff --git a/fs/internal.h b/fs/internal.h index 3e206d3e317c..4372d67a3753 100644 --- a/fs/internal.h +++ b/fs/internal.h @@ -102,6 +102,16 @@ extern void chroot_fs_refs(const struct path *, const struct path *); extern struct file *alloc_empty_file(int, const struct cred *); extern struct file *alloc_empty_file_noaccount(int, const struct cred *); +static inline void put_file_access(struct file *file) +{ + if ((file->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ) { + i_readcount_dec(file->f_inode); + } else if (file->f_mode & FMODE_WRITER) { + put_write_access(file->f_inode); + __mnt_drop_write(file->f_path.mnt); + } +} + /* * super.c */ diff --git a/fs/open.c b/fs/open.c index cf7e5c350a54..a81319b6177f 100644 --- a/fs/open.c +++ b/fs/open.c @@ -842,7 +842,9 @@ static int do_dentry_open(struct file *f, return 0; } - if (f->f_mode & FMODE_WRITE && !special_file(inode->i_mode)) { + if ((f->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ) { + i_readcount_inc(inode); + } else if (f->f_mode & FMODE_WRITE && !special_file(inode->i_mode)) { error = get_write_access(inode); if (unlikely(error)) goto cleanup_file; @@ -882,8 +884,6 @@ static int do_dentry_open(struct file *f, goto cleanup_all; } f->f_mode |= FMODE_OPENED; - if ((f->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ) - i_readcount_inc(inode); if ((f->f_mode & FMODE_READ) && likely(f->f_op->read || f->f_op->read_iter)) f->f_mode |= FMODE_CAN_READ; @@ -937,10 +937,7 @@ static int do_dentry_open(struct file *f, if (WARN_ON_ONCE(error > 0)) error = -EINVAL; fops_put(f->f_op); - if (f->f_mode & FMODE_WRITER) { - put_write_access(inode); - __mnt_drop_write(f->f_path.mnt); - } + put_file_access(f); cleanup_file: path_put(&f->f_path); f->f_path.mnt = NULL; -- 2.35.1