From patchwork Tue Aug 16 14:08:18 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Amir Goldstein X-Patchwork-Id: 12945003 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 CE7CCC25B0E for ; Tue, 16 Aug 2022 14:08:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234470AbiHPOIa (ORCPT ); Tue, 16 Aug 2022 10:08:30 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49534 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230009AbiHPOI2 (ORCPT ); Tue, 16 Aug 2022 10:08:28 -0400 Received: from mail-wr1-x42b.google.com (mail-wr1-x42b.google.com [IPv6:2a00:1450:4864:20::42b]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DA1F3326CC for ; Tue, 16 Aug 2022 07:08:24 -0700 (PDT) Received: by mail-wr1-x42b.google.com with SMTP id r16so3551363wrm.6 for ; Tue, 16 Aug 2022 07:08:24 -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=kmdIN0Xlen/pSXhbdzYshFcO4sR/SDxOgmdcF+pEKPs=; b=oYoLYrEXT8TxUR8bZLDMYX2L/IzEt/T95W+gh1UTs96ZwAvGtlVtJb5j+zmZSKqL5n i/LvATJXSGoQOe0rtfUmd5TkVNX3Hs8uZuM1h/SVglm2HTEXy9GKXdXj9KP35O+/lxEV E2e4wZ3uWQrCZ+HPC1yAEFC62hgM9JH6CXahbQ3KdR6q6EibGUjSb/0qM/XSl1bFRW4q tqEJLrCd6iaXWTT97Jern+Zy5G1jBUV3TE8kQSm+n8WcqyRV/mrU9PqLpONJKbVEhiKD XRrw8azy6hr1fBp2u/wP7HyseUIQdrlZusgGa/13NzXQiwyNZrnqlt4NglDWt2MMN+P7 L1/g== 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=kmdIN0Xlen/pSXhbdzYshFcO4sR/SDxOgmdcF+pEKPs=; b=NXsoTOaBthdp3RmSjAu3sOtiOtWfrjr1OLaBU3YtKqIUYNUaGFLx3TuF5Jb/PCRHBQ QlIZyM0xLUxNvDfU3ENid37x4HXbqSnw4e3d6rXFyVR6iY8I18NAVhADJXUw3TNSebZ0 4ZTFD/AEjXDZvDM5nuHYTg2+/XDDQ/OIcZ7MHQJfpERElClgvoweSAw5Lscegu3wR/f+ xOcUr1hL9CAAl3l3jeWvwHIjVgdohaqkzS69VIQQ1b4++P7Jfqka2G7FGojZunjWqC3o YHPreI7yE+6ULiXhNW6hCsUSuArev2TIOLuY5/a48ODZKPLer45RsfHmINS53zn6nj9x r+lA== X-Gm-Message-State: ACgBeo0+AA2ovvL94f03DEvtY3roZxK76TjgTAVjjAaBrkzwSDLl81Xd fYic0FwS0XQ8FUjbEZ8clOaBNYSqJck= X-Google-Smtp-Source: AA6agR7kuAWizvzaJoTjeX3Zz2KyQ+DEm9LjckAdluTIgFhceVcoEwJ7PfXZiIi2DhNtN6XnI9Tufg== X-Received: by 2002:a5d:6d0f:0:b0:220:76a3:b31d with SMTP id e15-20020a5d6d0f000000b0022076a3b31dmr12029840wrq.581.1660658903223; Tue, 16 Aug 2022 07:08:23 -0700 (PDT) Received: from localhost.localdomain ([77.137.66.49]) by smtp.gmail.com with ESMTPSA id bp15-20020a5d5a8f000000b0021ee65426a2sm10565538wrb.65.2022.08.16.07.08.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 16 Aug 2022 07:08:22 -0700 (PDT) From: Amir Goldstein To: Al Viro Cc: Jeff Layton , Chuck Lever , linux-fsdevel@vger.kernel.org Subject: [PATCH v2] locks: fix TOCTOU race when granting write lease Date: Tue, 16 Aug 2022 17:08:18 +0300 Message-Id: <20220816140818.708431-1-amir73il@gmail.com> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 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") Signed-off-by: Amir Goldstein Reviewed-by: Jeff Layton --- Hi Al, Per your request, here is v2 with moved helper. Jeff has suggested that I add kerneldoc, but I couldn't come up with a good description and didn't think it was very important, so I left it as is. Thanks, Amir. 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;