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 X-Spam-Level: X-Spam-Status: No, score=-19.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7693AC4338F for ; Mon, 16 Aug 2021 13:26:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 620E563292 for ; Mon, 16 Aug 2021 13:26:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240220AbhHPN1D (ORCPT ); Mon, 16 Aug 2021 09:27:03 -0400 Received: from mail.kernel.org ([198.145.29.99]:43332 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240388AbhHPNQp (ORCPT ); Mon, 16 Aug 2021 09:16:45 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 63583632EF; Mon, 16 Aug 2021 13:13:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1629119604; bh=an0t3BZUULDzdfiwNObU/fSO9ebQNPCwThTsWk57IEE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=QM79jUUDPVIhtDpGSEhyDdCs33Yz+P3eT3ydQa7KIIpReLK/Kn3UUGUa30FmwYckB 6e0yVbG+rwhW8JIb29imG9bMIAbGdAkrTeKW3htOgsrO17eBeOKh0iNLEPhXfFNIhs T9UFLsoNa/a5659Fnbax7iSOYyogbM9WvgjSibzk= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Miklos Szeredi , Sasha Levin , syzbot+579885d1a9a833336209@syzkaller.appspotmail.com Subject: [PATCH 5.13 089/151] ovl: fix deadlock in splice write Date: Mon, 16 Aug 2021 15:01:59 +0200 Message-Id: <20210816125447.013365592@linuxfoundation.org> X-Mailer: git-send-email 2.32.0 In-Reply-To: <20210816125444.082226187@linuxfoundation.org> References: <20210816125444.082226187@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: linux-kernel@vger.kernel.org From: Miklos Szeredi [ Upstream commit 9b91b6b019fda817eb52f728eb9c79b3579760bc ] 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 Signed-off-by: Sasha Levin --- fs/overlayfs/file.c | 47 ++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 46 insertions(+), 1 deletion(-) diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c index 4d53d3b7e5fe..d081faa55e83 100644 --- a/fs/overlayfs/file.c +++ b/fs/overlayfs/file.c @@ -392,6 +392,51 @@ 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; @@ -603,7 +648,7 @@ const struct file_operations ovl_file_operations = { .fadvise = ovl_fadvise, .flush = ovl_flush, .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, -- 2.30.2