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 lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 40518C7115B for ; Fri, 20 Jun 2025 00:12:01 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1uSPLR-0000eP-Ad; Thu, 19 Jun 2025 20:11:01 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1uSPLK-0000c6-Bo for qemu-devel@nongnu.org; Thu, 19 Jun 2025 20:10:54 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1uSPLI-0004pX-8W for qemu-devel@nongnu.org; Thu, 19 Jun 2025 20:10:54 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1750378251; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=bWiuPdGNiw6hej+OSFD3Xs/rvRXOuQm8S9rKave5hhI=; b=PQtFQEYCtwKxqCJCXiXLVy5YokQJKZvxWd3FywjQLi84PrZrOR1ObzXgmCJvL6n/KFeMrD VTIb4ct9k1L/qpv3gjp3+26CsMQ2A8UqnbEYBzVr2XlmhXZWzRvjhGyYgEgTM49n2fwtwc vdI1VaX4Jaq3RzcyG8jFfc3+AWtP8UU= Received: from mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-27-wJvCWWfGNXKRgSQ36bGaQA-1; Thu, 19 Jun 2025 20:10:48 -0400 X-MC-Unique: wJvCWWfGNXKRgSQ36bGaQA-1 X-Mimecast-MFC-AGG-ID: wJvCWWfGNXKRgSQ36bGaQA_1750378247 Received: from mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.93]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id C7EE31801BD8; Fri, 20 Jun 2025 00:10:46 +0000 (UTC) Received: from localhost (unknown [10.2.16.120]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id BBC2518003FC; Fri, 20 Jun 2025 00:10:45 +0000 (UTC) From: Stefan Hajnoczi To: qemu-devel@nongnu.org Cc: Hanna Reitz , Kevin Wolf , Stefan Weil , Paolo Bonzini , Fam Zheng , eblake@redhat.com, Stefano Garzarella , qemu-block@nongnu.org, Stefan Hajnoczi , Aarushi Mehta , hibriansong@gmail.com Subject: [PATCH v2 01/12] aio-posix: fix race between io_uring CQE and AioHandler deletion Date: Thu, 19 Jun 2025 20:08:17 -0400 Message-ID: <20250620000829.1426291-2-stefanha@redhat.com> In-Reply-To: <20250620000829.1426291-1-stefanha@redhat.com> References: <20250620000829.1426291-1-stefanha@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 Received-SPF: pass client-ip=170.10.129.124; envelope-from=stefanha@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -39 X-Spam_score: -4.0 X-Spam_bar: ---- X-Spam_report: (-4.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.897, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org When an AioHandler is enqueued on ctx->submit_list for removal, the fill_sq_ring() function will submit an io_uring POLL_REMOVE operation to cancel the in-flight POLL_ADD operation. There is a race when another thread enqueues an AioHandler for deletion on ctx->submit_list when the POLL_ADD CQE has already appeared. In that case POLL_REMOVE is unnecessary. The code already handled this, but forgot that the AioHandler itself is still on ctx->submit_list when the POLL_ADD CQE is being processed. It's unsafe to delete the AioHandler at that point in time (use-after-free). Solve this problem by keeping the AioHandler alive but setting a flag so that it will be deleted by fill_sq_ring() when it runs. Signed-off-by: Stefan Hajnoczi --- util/fdmon-io_uring.c | 26 +++++++++++++++++++------- 1 file changed, 19 insertions(+), 7 deletions(-) diff --git a/util/fdmon-io_uring.c b/util/fdmon-io_uring.c index b0d68bdc44..2e40fff09a 100644 --- a/util/fdmon-io_uring.c +++ b/util/fdmon-io_uring.c @@ -52,9 +52,10 @@ enum { FDMON_IO_URING_ENTRIES = 128, /* sq/cq ring size */ /* AioHandler::flags */ - FDMON_IO_URING_PENDING = (1 << 0), - FDMON_IO_URING_ADD = (1 << 1), - FDMON_IO_URING_REMOVE = (1 << 2), + FDMON_IO_URING_PENDING = (1 << 0), + FDMON_IO_URING_ADD = (1 << 1), + FDMON_IO_URING_REMOVE = (1 << 2), + FDMON_IO_URING_DELETE_AIO_HANDLER = (1 << 3), }; static inline int poll_events_from_pfd(int pfd_events) @@ -218,6 +219,9 @@ static void fill_sq_ring(AioContext *ctx) if (flags & FDMON_IO_URING_REMOVE) { add_poll_remove_sqe(ctx, node); } + if (flags & FDMON_IO_URING_DELETE_AIO_HANDLER) { + QLIST_INSERT_HEAD_RCU(&ctx->deleted_aio_handlers, node, node_deleted); + } } } @@ -241,7 +245,12 @@ static bool process_cqe(AioContext *ctx, */ flags = qatomic_fetch_and(&node->flags, ~FDMON_IO_URING_REMOVE); if (flags & FDMON_IO_URING_REMOVE) { - QLIST_INSERT_HEAD_RCU(&ctx->deleted_aio_handlers, node, node_deleted); + if (flags & FDMON_IO_URING_PENDING) { + /* Still on ctx->submit_list, defer deletion until fill_sq_ring() */ + qatomic_or(&node->flags, FDMON_IO_URING_DELETE_AIO_HANDLER); + } else { + QLIST_INSERT_HEAD_RCU(&ctx->deleted_aio_handlers, node, node_deleted); + } return false; } @@ -347,10 +356,13 @@ void fdmon_io_uring_destroy(AioContext *ctx) unsigned flags = qatomic_fetch_and(&node->flags, ~(FDMON_IO_URING_PENDING | FDMON_IO_URING_ADD | - FDMON_IO_URING_REMOVE)); + FDMON_IO_URING_REMOVE | + FDMON_IO_URING_DELETE_AIO_HANDLER)); - if (flags & FDMON_IO_URING_REMOVE) { - QLIST_INSERT_HEAD_RCU(&ctx->deleted_aio_handlers, node, node_deleted); + if ((flags & FDMON_IO_URING_REMOVE) || + (flags & FDMON_IO_URING_DELETE_AIO_HANDLER)) { + QLIST_INSERT_HEAD_RCU(&ctx->deleted_aio_handlers, + node, node_deleted); } QSLIST_REMOVE_HEAD_RCU(&ctx->submit_list, node_submitted); -- 2.49.0