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 6A93BC4332F for ; Mon, 6 Dec 2021 15:25:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240558AbhLFP3O (ORCPT ); Mon, 6 Dec 2021 10:29:14 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57302 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1385673AbhLFPZf (ORCPT ); Mon, 6 Dec 2021 10:25:35 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 79E0EC08EB53; Mon, 6 Dec 2021 07:15:47 -0800 (PST) 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 41AE3B81129; Mon, 6 Dec 2021 15:15:46 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5B50CC341C7; Mon, 6 Dec 2021 15:15:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1638803744; bh=rPlkrD5SPa1KlLDoeSe54Q8Pzd6Ufr6HwxgoaQwYB/I=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=aG52PJeUp3KxgKh3b7X/iJrUMNbARM+ylefD0F2UGpLYI6R804RTvQ+jgQziJB3EK 2lomFztHKQcMmR9Nvzb6sNenF8mw7XCt87xgRXimwPm6pftQzA2jwkTQsNs+akA0jX Lu5qE6hiU+fQxUjPFnNuVoB23vOfo5kl7wcpXhrA= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Miklos Szeredi , Stan Hu , syzbot+579885d1a9a833336209@syzkaller.appspotmail.com Subject: [PATCH 5.10 004/130] ovl: fix deadlock in splice write Date: Mon, 6 Dec 2021 15:55:21 +0100 Message-Id: <20211206145559.762796965@linuxfoundation.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20211206145559.607158688@linuxfoundation.org> References: <20211206145559.607158688@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: stable@vger.kernel.org From: Miklos Szeredi commit 9b91b6b019fda817eb52f728eb9c79b3579760bc upstream. There's possibility of an ABBA deadlock in case of a splice write to an overlayfs file and a concurrent splice write to a corresponding real file. The call chain for splice to an overlay file: -> do_splice [takes sb_writers on overlay file] -> do_splice_from -> iter_file_splice_write [takes pipe->mutex] -> vfs_iter_write ... -> ovl_write_iter [takes sb_writers on real file] And the call chain for splice to a real file: -> do_splice [takes sb_writers on real file] -> do_splice_from -> iter_file_splice_write [takes pipe->mutex] Syzbot successfully bisected this to commit 82a763e61e2b ("ovl: simplify file splice"). Fix by reverting the write part of the above commit and by adding missing bits from ovl_write_iter() into ovl_splice_write(). Fixes: 82a763e61e2b ("ovl: simplify file splice") Reported-and-tested-by: syzbot+579885d1a9a833336209@syzkaller.appspotmail.com Signed-off-by: Miklos Szeredi Cc: Stan Hu Signed-off-by: Greg Kroah-Hartman --- fs/overlayfs/file.c | 47 ++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 46 insertions(+), 1 deletion(-) --- a/fs/overlayfs/file.c +++ b/fs/overlayfs/file.c @@ -422,6 +422,51 @@ out_unlock: return ret; } +/* + * Calling iter_file_splice_write() directly from overlay's f_op may deadlock + * due to lock order inversion between pipe->mutex in iter_file_splice_write() + * and file_start_write(real.file) in ovl_write_iter(). + * + * So do everything ovl_write_iter() does and call iter_file_splice_write() on + * the real file. + */ +static ssize_t ovl_splice_write(struct pipe_inode_info *pipe, struct file *out, + loff_t *ppos, size_t len, unsigned int flags) +{ + struct fd real; + const struct cred *old_cred; + struct inode *inode = file_inode(out); + struct inode *realinode = ovl_inode_real(inode); + ssize_t ret; + + inode_lock(inode); + /* Update mode */ + ovl_copyattr(realinode, inode); + ret = file_remove_privs(out); + if (ret) + goto out_unlock; + + ret = ovl_real_fdget(out, &real); + if (ret) + goto out_unlock; + + old_cred = ovl_override_creds(inode->i_sb); + file_start_write(real.file); + + ret = iter_file_splice_write(pipe, real.file, ppos, len, flags); + + file_end_write(real.file); + /* Update size */ + ovl_copyattr(realinode, inode); + revert_creds(old_cred); + fdput(real); + +out_unlock: + inode_unlock(inode); + + return ret; +} + static int ovl_fsync(struct file *file, loff_t start, loff_t end, int datasync) { struct fd real; @@ -731,7 +776,7 @@ const struct file_operations ovl_file_op .compat_ioctl = ovl_compat_ioctl, #endif .splice_read = generic_file_splice_read, - .splice_write = iter_file_splice_write, + .splice_write = ovl_splice_write, .copy_file_range = ovl_copy_file_range, .remap_file_range = ovl_remap_file_range,