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 E6974C4321E for ; Mon, 5 Dec 2022 19:40:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234736AbiLETj7 (ORCPT ); Mon, 5 Dec 2022 14:39:59 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41710 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234767AbiLETj3 (ORCPT ); Mon, 5 Dec 2022 14:39:29 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2E6A363DB for ; Mon, 5 Dec 2022 11:36:48 -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 dfw.source.kernel.org (Postfix) with ESMTPS id C12DE61315 for ; Mon, 5 Dec 2022 19:36:47 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id D1ED8C433D7; Mon, 5 Dec 2022 19:36:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1670269007; bh=3i6zjMD7NFls4XmsmtAG04Gkllhd7DDOhsyKi9CoT2I=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=oGAs/cQxTwvg2kY4hVVID/hp9bItkjhY+/ju/nGSg6H2jxgjkxrAhOcXCKbEbOlde zntwF4Lz4O58RTdQ23eCNrvni0/mpM2k95mbaVQPVbfv9+degZ1/SM+M+jPXNQyKvT NQXInwuLkZvMJ5Q8YJBkSMc01+xVZFDkfZqxX55U= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Lin Ma , Pavel Begunkov , Jens Axboe Subject: [PATCH 5.15 092/120] io_uring/poll: fix poll_refs race with cancelation Date: Mon, 5 Dec 2022 20:10:32 +0100 Message-Id: <20221205190809.338219043@linuxfoundation.org> X-Mailer: git-send-email 2.38.1 In-Reply-To: <20221205190806.528972574@linuxfoundation.org> References: <20221205190806.528972574@linuxfoundation.org> User-Agent: quilt/0.67 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: Lin Ma [ upstream commit 12ad3d2d6c5b0131a6052de91360849e3e154846 ] There is an interesting race condition of poll_refs which could result in a NULL pointer dereference. The crash trace is like: KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f] CPU: 0 PID: 30781 Comm: syz-executor.2 Not tainted 6.0.0-g493ffd6605b2 #1 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014 RIP: 0010:io_poll_remove_entry io_uring/poll.c:154 [inline] RIP: 0010:io_poll_remove_entries+0x171/0x5b4 io_uring/poll.c:190 Code: ... RSP: 0018:ffff88810dfefba0 EFLAGS: 00010202 RAX: 0000000000000001 RBX: 0000000000000000 RCX: 0000000000040000 RDX: ffffc900030c4000 RSI: 000000000003ffff RDI: 0000000000040000 RBP: 0000000000000008 R08: ffffffff9764d3dd R09: fffffbfff3836781 R10: fffffbfff3836781 R11: 0000000000000000 R12: 1ffff11003422d60 R13: ffff88801a116b04 R14: ffff88801a116ac0 R15: dffffc0000000000 FS: 00007f9c07497700(0000) GS:ffff88811a600000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007ffb5c00ea98 CR3: 0000000105680005 CR4: 0000000000770ef0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 PKRU: 55555554 Call Trace: io_apoll_task_func+0x3f/0xa0 io_uring/poll.c:299 handle_tw_list io_uring/io_uring.c:1037 [inline] tctx_task_work+0x37e/0x4f0 io_uring/io_uring.c:1090 task_work_run+0x13a/0x1b0 kernel/task_work.c:177 get_signal+0x2402/0x25a0 kernel/signal.c:2635 arch_do_signal_or_restart+0x3b/0x660 arch/x86/kernel/signal.c:869 exit_to_user_mode_loop kernel/entry/common.c:166 [inline] exit_to_user_mode_prepare+0xc2/0x160 kernel/entry/common.c:201 __syscall_exit_to_user_mode_work kernel/entry/common.c:283 [inline] syscall_exit_to_user_mode+0x58/0x160 kernel/entry/common.c:294 entry_SYSCALL_64_after_hwframe+0x63/0xcd The root cause for this is a tiny overlooking in io_poll_check_events() when cocurrently run with poll cancel routine io_poll_cancel_req(). The interleaving to trigger use-after-free: CPU0 | CPU1 | io_apoll_task_func() | io_poll_cancel_req() io_poll_check_events() | // do while first loop | v = atomic_read(...) | // v = poll_refs = 1 | ... | io_poll_mark_cancelled() | atomic_or() | // poll_refs = IO_POLL_CANCEL_FLAG | 1 | atomic_sub_return(...) | // poll_refs = IO_POLL_CANCEL_FLAG | // loop continue | | | io_poll_execute() | io_poll_get_ownership() | // poll_refs = IO_POLL_CANCEL_FLAG | 1 | // gets the ownership v = atomic_read(...) | // poll_refs not change | | if (v & IO_POLL_CANCEL_FLAG) | return -ECANCELED; | // io_poll_check_events return | // will go into | // io_req_complete_failed() free req | | | io_apoll_task_func() | // also go into io_req_complete_failed() And the interleaving to trigger the kernel WARNING: CPU0 | CPU1 | io_apoll_task_func() | io_poll_cancel_req() io_poll_check_events() | // do while first loop | v = atomic_read(...) | // v = poll_refs = 1 | ... | io_poll_mark_cancelled() | atomic_or() | // poll_refs = IO_POLL_CANCEL_FLAG | 1 | atomic_sub_return(...) | // poll_refs = IO_POLL_CANCEL_FLAG | // loop continue | | v = atomic_read(...) | // v = IO_POLL_CANCEL_FLAG | | io_poll_execute() | io_poll_get_ownership() | // poll_refs = IO_POLL_CANCEL_FLAG | 1 | // gets the ownership | WARN_ON_ONCE(!(v & IO_POLL_REF_MASK))) | // v & IO_POLL_REF_MASK = 0 WARN | | | io_apoll_task_func() | // also go into io_req_complete_failed() By looking up the source code and communicating with Pavel, the implementation of this atomic poll refs should continue the loop of io_poll_check_events() just to avoid somewhere else to grab the ownership. Therefore, this patch simply adds another AND operation to make sure the loop will stop if it finds the poll_refs is exactly equal to IO_POLL_CANCEL_FLAG. Since io_poll_cancel_req() grabs ownership and will finally make its way to io_req_complete_failed(), the req will be reclaimed as expected. Fixes: aa43477b0402 ("io_uring: poll rework") Signed-off-by: Lin Ma Reviewed-by: Pavel Begunkov [axboe: tweak description and code style] Signed-off-by: Jens Axboe Signed-off-by: Pavel Begunkov Signed-off-by: Greg Kroah-Hartman --- fs/io_uring.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -5512,7 +5512,8 @@ static int io_poll_check_events(struct i * Release all references, retry if someone tried to restart * task_work while we were executing it. */ - } while (atomic_sub_return(v & IO_POLL_REF_MASK, &req->poll_refs)); + } while (atomic_sub_return(v & IO_POLL_REF_MASK, &req->poll_refs) & + IO_POLL_REF_MASK); return 1; }