From patchwork Mon Oct 15 15:04:18 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jann Horn X-Patchwork-Id: 10642029 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 5473717D2 for ; Mon, 15 Oct 2018 15:04:31 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 431C929279 for ; Mon, 15 Oct 2018 15:04:31 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 35CFA29429; Mon, 15 Oct 2018 15:04:31 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.5 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI, USER_IN_DEF_DKIM_WL autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id BAE2729279 for ; Mon, 15 Oct 2018 15:04:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726576AbeJOWuH (ORCPT ); Mon, 15 Oct 2018 18:50:07 -0400 Received: from mail-vs1-f73.google.com ([209.85.217.73]:35545 "EHLO mail-vs1-f73.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726550AbeJOWuH (ORCPT ); Mon, 15 Oct 2018 18:50:07 -0400 Received: by mail-vs1-f73.google.com with SMTP id x7so9416572vsf.2 for ; Mon, 15 Oct 2018 08:04:29 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:message-id:mime-version:subject:from:to:cc; bh=iyDE8NnRHXGUj+mrrGahTGfEtbQ6Dv/IBRddY6oIEjQ=; b=VIxSv1M116xvnMupu2kUQzZdB8q6HRSFDxDDNmyDX59w1V98ykqj81ppNvRH+I/mXO qyl65SmIU9KmYlSTRFtL5ijMi8wTIYFypw5VcjC/nKfDONV7cIBwZKJwt4Mr9My9QIF0 wD0dgW7DoXXQv53JHd/hPDmfN1LxNXMYjBhlsYcSEaxw+18JXl04rSLINWi4W1H7rc/3 5LWc8wkNwGJlHgm0uoZ2m0aPXqeMDymo47mFheO8OK0xM/38W7lSq6ik8j8os4JHhVEr r4SilP3rGUHqn0N+/qkCDAKkAaxXU3dkmW9RTyMhF5tD5Omn18L9h+hs8t8panKUfYQL aOeg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:message-id:mime-version:subject:from:to:cc; bh=iyDE8NnRHXGUj+mrrGahTGfEtbQ6Dv/IBRddY6oIEjQ=; b=pYHtJIp8kiXQeiVbgwjKi/6/oCsUMZaMfaDahXrpwwDlGA18ZGhqnZJaiQV4heKdIw IpPnLe7zttEHP4riR86zWzZ5i+F9R2Y1hxFqcJIS7w9j+cdlMS7pOkveF41e6VABG3xE JbVaS0cMqxiIQGSPxGHCRWrPoFSosOWbCLXeBzfwP7DmzFA4DVUr/oUU4R5Kijxraggw QteLbQ0Kz2c1CUPKI2DO9llvWlmgFlQbTkFVAoFdX8icZRIdZW5CaYbIkRqFl0iN7ZNI a6Ce2pLr0f6zdl6bZekHNER4JyVWvy/oRalw1SO2SIt8oPRTx3zNYZIGDboGTC3j4qGi XucA== X-Gm-Message-State: ABuFfogFT70+77xNXW3eggc70JGhmEQGV8SXawA3tRzLLeYhA2ID/q1j 8CRCMMmkAWx7zLMszVkWDgd2faC9ZQ== X-Google-Smtp-Source: ACcGV62hGzBbfZFTUVdwgCf8OOhIEdh3lwBeATP4cphXOKi86QJ7ce2YIVqhy5zw7AGX9+N+ZdhCZeq+Tw== X-Received: by 2002:a1f:c4c2:: with SMTP id u185mr11982763vkf.19.1539615868846; Mon, 15 Oct 2018 08:04:28 -0700 (PDT) Date: Mon, 15 Oct 2018 17:04:18 +0200 Message-Id: <20181015150420.2096-1-jannh@google.com> Mime-Version: 1.0 X-Mailer: git-send-email 2.19.0.605.g01d371f741-goog Subject: [PATCH 1/2] splice: don't merge into linked buffers From: Jann Horn To: Al Viro , Miklos Szeredi , Jens Axboe , Jens Axboe , jannh@google.com Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Kees Cook , Eric Biggers Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP Before this patch, it was possible for two pipes to affect each other after data had been transferred between them with tee(): ============ $ cat tee_test.c int main(void) { int pipe_a[2]; if (pipe(pipe_a)) err(1, "pipe"); int pipe_b[2]; if (pipe(pipe_b)) err(1, "pipe"); if (write(pipe_a[1], "abcd", 4) != 4) err(1, "write"); if (tee(pipe_a[0], pipe_b[1], 2, 0) != 2) err(1, "tee"); if (write(pipe_b[1], "xx", 2) != 2) err(1, "write"); char buf[5]; if (read(pipe_a[0], buf, 4) != 4) err(1, "read"); buf[4] = 0; printf("got back: '%s'\n", buf); } $ gcc -o tee_test tee_test.c $ ./tee_test got back: 'abxx' $ ============ Fix it by explicitly marking buffers as mergeable and clearing that flag in splice_pipe_to_pipe() and link_pipe(). Cc: Fixes: 7c77f0b3f920 ("splice: implement pipe to pipe splicing") Fixes: 70524490ee2e ("[PATCH] splice: add support for sys_tee()") Signed-off-by: Jann Horn --- Cleanup in the next patch, to simplify backporting. fs/pipe.c | 5 +++-- fs/splice.c | 6 ++++++ include/linux/pipe_fs_i.h | 8 ++++++++ 3 files changed, 17 insertions(+), 2 deletions(-) diff --git a/fs/pipe.c b/fs/pipe.c index bdc5d3c0977d..4e2eee77f855 100644 --- a/fs/pipe.c +++ b/fs/pipe.c @@ -379,7 +379,8 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from) struct pipe_buffer *buf = pipe->bufs + lastbuf; int offset = buf->offset + buf->len; - if (buf->ops->can_merge && offset + chars <= PAGE_SIZE) { + if (buf->ops->can_merge && offset + chars <= PAGE_SIZE && + (buf->flags & PIPE_BUF_FLAG_MAYMERGE)) { ret = pipe_buf_confirm(pipe, buf); if (ret) goto out; @@ -439,7 +440,7 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from) buf->ops = &anon_pipe_buf_ops; buf->offset = 0; buf->len = copied; - buf->flags = 0; + buf->flags = PIPE_BUF_FLAG_MAYMERGE; if (is_packetized(filp)) { buf->ops = &packet_pipe_buf_ops; buf->flags = PIPE_BUF_FLAG_PACKET; diff --git a/fs/splice.c b/fs/splice.c index b3daa971f597..111977c80dfd 100644 --- a/fs/splice.c +++ b/fs/splice.c @@ -1593,6 +1593,9 @@ static int splice_pipe_to_pipe(struct pipe_inode_info *ipipe, */ obuf->flags &= ~PIPE_BUF_FLAG_GIFT; + /* We can't merge data into a buffer we don't own. */ + obuf->flags &= ~PIPE_BUF_FLAG_MAYMERGE; + obuf->len = len; opipe->nrbufs++; ibuf->offset += obuf->len; @@ -1667,6 +1670,9 @@ static int link_pipe(struct pipe_inode_info *ipipe, */ obuf->flags &= ~PIPE_BUF_FLAG_GIFT; + /* We can't merge data into a buffer we don't own. */ + obuf->flags &= ~PIPE_BUF_FLAG_MAYMERGE; + if (obuf->len > len) obuf->len = len; diff --git a/include/linux/pipe_fs_i.h b/include/linux/pipe_fs_i.h index 5a3bb3b7c9ad..8893711f9171 100644 --- a/include/linux/pipe_fs_i.h +++ b/include/linux/pipe_fs_i.h @@ -8,6 +8,14 @@ #define PIPE_BUF_FLAG_ATOMIC 0x02 /* was atomically mapped */ #define PIPE_BUF_FLAG_GIFT 0x04 /* page is a gift */ #define PIPE_BUF_FLAG_PACKET 0x08 /* read() as a packet */ +/* + * Set this flag if the generic pipe read/write may coalesce data into an + * existing buffer. If this is not set, a new pipe page segment is always used + * for new data. + * When pipe data is copied by reference (as in the tee() syscall), this flag + * must be cleared on the copy. + */ +#define PIPE_BUF_FLAG_MAYMERGE 0x10 /** * struct pipe_buffer - a linux kernel pipe buffer