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 B2293C25B0E for ; Tue, 16 Aug 2022 14:53:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235997AbiHPOxZ (ORCPT ); Tue, 16 Aug 2022 10:53:25 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38792 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234898AbiHPOxY (ORCPT ); Tue, 16 Aug 2022 10:53:24 -0400 Received: from mail-wr1-x433.google.com (mail-wr1-x433.google.com [IPv6:2a00:1450:4864:20::433]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4E68E113E for ; Tue, 16 Aug 2022 07:53:23 -0700 (PDT) Received: by mail-wr1-x433.google.com with SMTP id bu15so4429700wrb.7 for ; Tue, 16 Aug 2022 07:53:23 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc; bh=4llRFXnBcaQLdHTCgiOVHAzZqek7JSHT+X10DQaIJVA=; b=FCGe/wd30FXA5rdSvutNEet3IEKbI2M0+77NNVFFk2Q+ov5HUEGDDhAe+pTL3sOWa1 eF1+FII/RCzch8q0fxmOmjH78cOrwsyW8lxmZGi9rdcyGBEa/JDi8hsMVMPtyuwMcl2m 5LoSq1iNiSfG0QAcrLBZtrnTVjSpGopMZ11BXNa3bJUGIdvAonDr0SFzv5wdzNSCdlCy 0antBLSpx/Xf7aIeED3U1TTKRbvNK18Xqeg5+Ou3QyTSMQ+TkFn5E+uivCruq86dvzIE ddxr42+n7QS2uRsHpofdfRgMGLMaeWO7SFlwPMQ9yPjCjRCxVMVgcGZxWJReBjIL/gu0 T3Gg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-message-state:from:to:cc; bh=4llRFXnBcaQLdHTCgiOVHAzZqek7JSHT+X10DQaIJVA=; b=b6KFEGwf6g2h245+33JmxgCCXsrnbxMIyWKh4JcgtOyDMPiEjvU+/HDM3eqWC5gV2T YpnsWQKwQK5UyF8v4zN8bZTDkqa5tqfQLzi7kebYCZDNPhtHcR3RpzwmWeK7HWyPRboW Gw0zBLNmlbgNZJMryi/1zMZxI2XrxCsf2vnpYsLYD/byq91qd9aGadJLC9FbbEkRPYIs agzX8IFx4cLN3EUlv8dkR5vMVlRI0jkHBgzuZGofYu+vU93rCYNWxc/+TppYiO/QJ90Y Cqtye3P0+6+n2Gn9RgiGjYv8O7AfuYpaLRVzugls4fiXeJVLiBc0Up4edT6Hc4imQlUx lTGQ== X-Gm-Message-State: ACgBeo0KNjemdEzCdGJBR85VA7vSA2ot1HWQBU46EVDEapMy0W/LJVBO UHzSzWsc7XeUBRoRjCIEwh26q6B0heU= X-Google-Smtp-Source: AA6agR47opgfylJC4T5TsfWONvWSsQJL1ztvl1z3y0Y6MZsyNygV4NNIL3J/PYzpY8k2XyoUISWS9A== X-Received: by 2002:adf:e9c8:0:b0:224:f896:94bc with SMTP id l8-20020adfe9c8000000b00224f89694bcmr7416886wrn.635.1660661601824; Tue, 16 Aug 2022 07:53:21 -0700 (PDT) Received: from localhost.localdomain ([77.137.66.49]) by smtp.gmail.com with ESMTPSA id b6-20020a05600c4e0600b003a5f4fccd4asm7569882wmq.35.2022.08.16.07.53.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 16 Aug 2022 07:53:21 -0700 (PDT) From: Amir Goldstein To: Al Viro Cc: Jeff Layton , Chuck Lever , linux-fsdevel@vger.kernel.org Subject: [PATCH v3] locks: fix TOCTOU race when granting write lease Date: Tue, 16 Aug 2022 17:53:17 +0300 Message-Id: <20220816145317.710368-1-amir73il@gmail.com> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org 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 --- Hi Al, Added Jeff's RVB assuming you will be taking this patch. Thanks, Amir. Changes since v2: - Add RVB Jeff Changes since v1: - Move helper to internal.h 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 87e96b9024ce..31861e6c3eff 100644 --- a/fs/internal.h +++ b/fs/internal.h @@ -101,6 +101,16 @@ 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 8a813fa5ca56..a98572585815 100644 --- a/fs/open.c +++ b/fs/open.c @@ -840,7 +840,9 @@ 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; @@ -880,8 +882,6 @@ 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; @@ -935,10 +935,7 @@ 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; -- 2.25.1