From nobody Fri Dec 19 22:02:55 2025 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 91530C38A2D for ; Mon, 24 Oct 2022 13:56:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236831AbiJXN4a (ORCPT ); Mon, 24 Oct 2022 09:56:30 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42906 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236839AbiJXNyT (ORCPT ); Mon, 24 Oct 2022 09:54:19 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 12765BD067; Mon, 24 Oct 2022 05:43:56 -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 dfw.source.kernel.org (Postfix) with ESMTPS id E1185612B9; Mon, 24 Oct 2022 12:43:54 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 02977C433D6; Mon, 24 Oct 2022 12:43:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1666615434; bh=pDb1qSlX5k+7QmuGyJdhWjYpgsjs5GTh4TeBNyLE3+E=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=fuJybRC8HsvBSM0VtV59Fu5ffAL+n7teogp5cXfwUT3stiaH1o360rWg4FY8uPXlI rRjrXA52J1biv0Uk1Xg22RMKbAiTZOCSM59HcBNqhqskfMVSO5QHkuWJShEYsajdF4 S3OzfwyyyyqWZz//z9wtyLOWO8BeQsmBGp77nIcw= 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 5.15 249/530] locks: fix TOCTOU race when granting write lease Date: Mon, 24 Oct 2022 13:29:53 +0200 Message-Id: <20221024113056.381976118@linuxfoundation.org> X-Mailer: git-send-email 2.38.1 In-Reply-To: <20221024113044.976326639@linuxfoundation.org> References: <20221024113044.976326639@linuxfoundation.org> User-Agent: quilt/0.67 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" 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 l= ease") 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 e8c9016703ad..6f297f9782fc 100644 --- a/fs/file_table.c +++ b/fs/file_table.c @@ -284,12 +284,7 @@ static void __fput(struct file *file) } fops_put(file->f_op); put_pid(file->f_owner.pid); - if ((mode & (FMODE_READ | FMODE_WRITE)) =3D=3D 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 4f1fe6d08866..9075490f21a6 100644 --- a/fs/internal.h +++ b/fs/internal.h @@ -100,6 +100,16 @@ 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 *); =20 +static inline void put_file_access(struct file *file) +{ + if ((file->f_mode & (FMODE_READ | FMODE_WRITE)) =3D=3D 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 1ba1d2ab2ef0..5e322f188e83 100644 --- a/fs/open.c +++ b/fs/open.c @@ -786,7 +786,9 @@ static int do_dentry_open(struct file *f, return 0; } =20 - if (f->f_mode & FMODE_WRITE && !special_file(inode->i_mode)) { + if ((f->f_mode & (FMODE_READ | FMODE_WRITE)) =3D=3D FMODE_READ) { + i_readcount_inc(inode); + } else if (f->f_mode & FMODE_WRITE && !special_file(inode->i_mode)) { error =3D get_write_access(inode); if (unlikely(error)) goto cleanup_file; @@ -826,8 +828,6 @@ static int do_dentry_open(struct file *f, goto cleanup_all; } f->f_mode |=3D FMODE_OPENED; - if ((f->f_mode & (FMODE_READ | FMODE_WRITE)) =3D=3D 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 |=3D FMODE_CAN_READ; @@ -880,10 +880,7 @@ static int do_dentry_open(struct file *f, if (WARN_ON_ONCE(error > 0)) error =3D -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 =3D NULL; --=20 2.35.1