From patchwork Mon Mar 14 11:54:54 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg KH X-Patchwork-Id: 551219 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 85770C43217 for ; Mon, 14 Mar 2022 12:23:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236710AbiCNMYb (ORCPT ); Mon, 14 Mar 2022 08:24:31 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49046 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S243949AbiCNMVZ (ORCPT ); Mon, 14 Mar 2022 08:21:25 -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 3165413D40; Mon, 14 Mar 2022 05:19:26 -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 A078B608C4; Mon, 14 Mar 2022 12:19:25 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 062E3C340E9; Mon, 14 Mar 2022 12:19:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1647260365; bh=qrjcQzJJwJt0h45ZjSQPyEjka1WJolCH3qzCphW+dps=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=vbD+EziwFqlQFJZKw2A/HCmXr9IknVKjxICznKCT6bAHgplU/mhfpUE0non3iD4vM yH3mZFjAoPLjJbuXV+0Wp5mgUwITPaRvUUVjkv77xQl9M02EoyRKm9NACWW4ESbfcs XWDyH/UevMrPw0GN0Fi+m19VG2o9d2SwI0gN0itE= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Jann Horn , David Howells , Linus Torvalds Subject: [PATCH 5.16 111/121] watch_queue: Fix lack of barrier/sync/lock between post and read Date: Mon, 14 Mar 2022 12:54:54 +0100 Message-Id: <20220314112747.206977163@linuxfoundation.org> X-Mailer: git-send-email 2.35.1 In-Reply-To: <20220314112744.120491875@linuxfoundation.org> References: <20220314112744.120491875@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: David Howells commit 2ed147f015af2b48f41c6f0b6746aa9ea85c19f3 upstream. There's nothing to synchronise post_one_notification() versus pipe_read(). Whilst posting is done under pipe->rd_wait.lock, the reader only takes pipe->mutex which cannot bar notification posting as that may need to be made from contexts that cannot sleep. Fix this by setting pipe->head with a barrier in post_one_notification() and reading pipe->head with a barrier in pipe_read(). If that's not sufficient, the rd_wait.lock will need to be taken, possibly in a ->confirm() op so that it only applies to notifications. The lock would, however, have to be dropped before copy_page_to_iter() is invoked. Fixes: c73be61cede5 ("pipe: Add general notification queue support") Reported-by: Jann Horn Signed-off-by: David Howells Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- fs/pipe.c | 3 ++- kernel/watch_queue.c | 2 +- 2 files changed, 3 insertions(+), 2 deletions(-) --- a/fs/pipe.c +++ b/fs/pipe.c @@ -252,7 +252,8 @@ pipe_read(struct kiocb *iocb, struct iov */ was_full = pipe_full(pipe->head, pipe->tail, pipe->max_usage); for (;;) { - unsigned int head = pipe->head; + /* Read ->head with a barrier vs post_one_notification() */ + unsigned int head = smp_load_acquire(&pipe->head); unsigned int tail = pipe->tail; unsigned int mask = pipe->ring_size - 1; --- a/kernel/watch_queue.c +++ b/kernel/watch_queue.c @@ -113,7 +113,7 @@ static bool post_one_notification(struct buf->offset = offset; buf->len = len; buf->flags = PIPE_BUF_FLAG_WHOLE; - pipe->head = head + 1; + smp_store_release(&pipe->head, head + 1); /* vs pipe_read() */ if (!test_and_clear_bit(note, wqueue->notes_bitmap)) { spin_unlock_irq(&pipe->rd_wait.lock);