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 C4207C433FE for ; Tue, 22 Nov 2022 18:47:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234454AbiKVSrQ (ORCPT ); Tue, 22 Nov 2022 13:47:16 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49490 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231519AbiKVSrO (ORCPT ); Tue, 22 Nov 2022 13:47:14 -0500 Received: from mail-yb1-xb2f.google.com (mail-yb1-xb2f.google.com [IPv6:2607:f8b0:4864:20::b2f]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5C5EF7FC2E for ; Tue, 22 Nov 2022 10:47:13 -0800 (PST) Received: by mail-yb1-xb2f.google.com with SMTP id k84so18372577ybk.3 for ; Tue, 22 Nov 2022 10:47:13 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:from:to:cc:subject:date:message-id:reply-to; bh=dTOA9Ph35CYeJ8dbWo1cP4Zrrfu9iAGIJB5Su8F8/h8=; b=C5YtO03xDsrZ8sonthtSzPrBMVSXWomGZmMAtFkFeyOeWQqusJQYrHZcAcPZKJgeBl xnvGhCWfr30rghBTk/W/RIIMuG/0CgHPXapTYX+Ioqkbl8q7qMTLiCYBrrPN1pPviPYF aMJ6Cui/L9IerPuKBLHSed8o0zgztTrlQolKQC4T1LDV3CfVMkFsKz1eepmWvCxAdymK JXlP0X+fy5yu95kKSTI98kUUHp1D/Z/aTUM03Ho7Kq1kdjnWd9iOkra65P+JYrk1yofR FRtbtc0ktvqweM2H753Yucj/3yHJS80Id6RR8TvRjmT8t9Vwl6VNaa9RTMYHapN8Apof lOZA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=dTOA9Ph35CYeJ8dbWo1cP4Zrrfu9iAGIJB5Su8F8/h8=; b=k3zipBw2Ea2GZSJzHzr9A0QoGDeD2ohLxGKr/Jm/MXe5p202j2Izcd3o5P3I8QSJAO nqPg2acfSG5Z6RNMx8RAe1IWZklVx/UksrMdvD/ZZvDHlL5ptw3InIRZIh5gUD6SP/rI zDGvWDdGJH+fhaar20it10aYwSh3762XPue67yP5id8UyvY4Z+Prmu99Nc110pRZ2o2e 030ACMj4nUQCto9y/SvxPArVfiFK9Rq2zH571gTBnlU501gjpuMM3N4lwo3rlkPTRU5O N/JIVbpAEIFVXGPTkPDXacYClX7sMmq9xfVsZ+rpxo9MNFvzm6k0b83T+zoF4Cidlf4j cRfQ== X-Gm-Message-State: ANoB5pmk2ByYkk69enAkKxPcpvX5fsCobDh1kepuOK6ZFUp98C1m1bRm hzMUMQcIIFsO6TfR9DSnrXoJhSAwk963IZON+wJaxXDLRm8aSg== X-Google-Smtp-Source: AA0mqf5WNe9llKT+N0TL0EfvDLU9nHv38RyeLQsGH4yX3TOpkduZi81IigeCJsQN+pc88l2NUuZvs5sQi2LUyHuC2m8= X-Received: by 2002:a25:d914:0:b0:6e1:547c:7a43 with SMTP id q20-20020a25d914000000b006e1547c7a43mr22973792ybg.231.1669142832207; Tue, 22 Nov 2022 10:47:12 -0800 (PST) MIME-Version: 1.0 References: <20221120090213.922567-1-syoshida@redhat.com> <20221123.031005.476714651315933198.syoshida@redhat.com> In-Reply-To: <20221123.031005.476714651315933198.syoshida@redhat.com> From: Eric Dumazet Date: Tue, 22 Nov 2022 10:47:01 -0800 Message-ID: Subject: Re: [PATCH v2] net: tun: Fix use-after-free in tun_detach() To: Shigeru Yoshida , Jason Wang Cc: davem@davemloft.net, kuba@kernel.org, pabeni@redhat.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com, syzbot+106f9b687cd64ee70cd1@syzkaller.appspotmail.com Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Nov 22, 2022 at 10:10 AM Shigeru Yoshida wrote: > > Hi Eric, > > On Mon, 21 Nov 2022 08:47:17 -0800, Eric Dumazet wrote: > > On Sun, Nov 20, 2022 at 1:02 AM Shigeru Yoshida wrote: > >> > >> syzbot reported use-after-free in tun_detach() [1]. This causes call > >> trace like below: > >> > >> ================================================================== > >> BUG: KASAN: use-after-free in notifier_call_chain+0x1ee/0x200 kernel/notifier.c:75 > >> Read of size 8 at addr ffff88807324e2a8 by task syz-executor.0/3673 > >> > >> CPU: 0 PID: 3673 Comm: syz-executor.0 Not tainted 6.1.0-rc5-syzkaller-00044-gcc675d22e422 #0 > >> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022 > >> Call Trace: > >> > >> __dump_stack lib/dump_stack.c:88 [inline] > >> dump_stack_lvl+0xd1/0x138 lib/dump_stack.c:106 > >> print_address_description mm/kasan/report.c:284 [inline] > >> print_report+0x15e/0x461 mm/kasan/report.c:395 > >> kasan_report+0xbf/0x1f0 mm/kasan/report.c:495 > >> notifier_call_chain+0x1ee/0x200 kernel/notifier.c:75 > >> call_netdevice_notifiers_info+0x86/0x130 net/core/dev.c:1942 > >> call_netdevice_notifiers_extack net/core/dev.c:1983 [inline] > >> call_netdevice_notifiers net/core/dev.c:1997 [inline] > >> netdev_wait_allrefs_any net/core/dev.c:10237 [inline] > >> netdev_run_todo+0xbc6/0x1100 net/core/dev.c:10351 > >> tun_detach drivers/net/tun.c:704 [inline] > >> tun_chr_close+0xe4/0x190 drivers/net/tun.c:3467 > >> __fput+0x27c/0xa90 fs/file_table.c:320 > >> task_work_run+0x16f/0x270 kernel/task_work.c:179 > >> exit_task_work include/linux/task_work.h:38 [inline] > >> do_exit+0xb3d/0x2a30 kernel/exit.c:820 > >> do_group_exit+0xd4/0x2a0 kernel/exit.c:950 > >> get_signal+0x21b1/0x2440 kernel/signal.c:2858 > >> arch_do_signal_or_restart+0x86/0x2300 arch/x86/kernel/signal.c:869 > >> exit_to_user_mode_loop kernel/entry/common.c:168 [inline] > >> exit_to_user_mode_prepare+0x15f/0x250 kernel/entry/common.c:203 > >> __syscall_exit_to_user_mode_work kernel/entry/common.c:285 [inline] > >> syscall_exit_to_user_mode+0x1d/0x50 kernel/entry/common.c:296 > >> do_syscall_64+0x46/0xb0 arch/x86/entry/common.c:86 > >> entry_SYSCALL_64_after_hwframe+0x63/0xcd > >> > >> The cause of the issue is that sock_put() from __tun_detach() drops > >> last reference count for struct net, and then notifier_call_chain() > >> from netdev_state_change() accesses that struct net. > >> > >> This patch fixes the issue by calling sock_put() from tun_detach() > >> after all necessary accesses for the struct net has done. > >> > >> Fixes: 83c1f36f9880 ("tun: send netlink notification when the device is modified") > >> Reported-by: syzbot+106f9b687cd64ee70cd1@syzkaller.appspotmail.com > >> Link: https://syzkaller.appspot.com/bug?id=96eb7f1ce75ef933697f24eeab928c4a716edefe [1] > >> Signed-off-by: Shigeru Yoshida > >> --- > >> v2: > >> - Include symbolic stack trace > >> - Add Fixes and Reported-by tags > >> v1: https://lore.kernel.org/all/20221119075615.723290-1-syoshida@redhat.com/ > >> --- > >> drivers/net/tun.c | 6 +++++- > >> 1 file changed, 5 insertions(+), 1 deletion(-) > >> > >> diff --git a/drivers/net/tun.c b/drivers/net/tun.c > >> index 7a3ab3427369..ce9fcf4c8ef4 100644 > >> --- a/drivers/net/tun.c > >> +++ b/drivers/net/tun.c > >> @@ -686,7 +686,6 @@ static void __tun_detach(struct tun_file *tfile, bool clean) > >> if (tun) > >> xdp_rxq_info_unreg(&tfile->xdp_rxq); > >> ptr_ring_cleanup(&tfile->tx_ring, tun_ptr_free); > >> - sock_put(&tfile->sk); > >> } > >> } > >> > >> @@ -702,6 +701,11 @@ static void tun_detach(struct tun_file *tfile, bool clean) > >> if (dev) > >> netdev_state_change(dev); > >> rtnl_unlock(); > >> + > >> + if (clean) { > > > > Would you mind explaining (a comment would be nice) why this barrier is needed ? > > I thought that tfile is accessed with rcu_lock(), so I put > synchronize_rcu() here. Please let me know if I misunderstand the > concept of rcu (I'm losing my confidence...). > Addin Jason for comments. If an RCU grace period was needed before commit 83c1f36f9880 ("tun: send netlink notification when the device is modified"), would we need another patch ? Also sock_flag(sk, SOCK_RCU_FREE) would probably be better than adding a synchronize_rcu() (if again a grace period is needed) > Thanks, > Shigeru > > > > > Thanks. > > > >> + synchronize_rcu(); > >> + sock_put(&tfile->sk); > >> + } > >> } > >> > >> static void tun_detach_all(struct net_device *dev) > >> -- > >> 2.38.1 > >> > > >