From patchwork Fri Mar 8 20:01:21 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Kuniyuki Iwashima X-Patchwork-Id: 13587236 Received: from smtp-fw-9106.amazon.com (smtp-fw-9106.amazon.com [207.171.188.206]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 37F205A4C0; Fri, 8 Mar 2024 20:09:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=207.171.188.206 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1709928593; cv=none; b=jh6SIdobLIKeVks6xMMrGycfTsf7AURs4lUuTP7W4dG6WplFXsQ9W9Jch5YjvYxgkJ+uidE/e2s/DsRoNbHGNlLixuhr8QGcMkwWZtgZpO+YaAR5zMdTs14JwN9MLLi+4u6RmHZzjasOipbatvAxtqr+KszIdGbpme5Acsfm/Qo= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1709928593; c=relaxed/simple; bh=8hXZFL121T9bjIjd3Lvj+LaaVX8zsYOI5YsxiVHmFjg=; h=From:To:CC:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=cgtg4LTRz7lDb2kgPk2xdvAhal68gGR2LLkQbCndVh7XMcWTXXK0ymc8aPDGdUyt5mrq45C+j0FlOYagjsNNqGJhPY32TWkusetaq3JXTfH7SqUFAAHF5Nx8n91WtnadAu9hTpBCOaEFrn/yKHDmdu3CjmrI3flWpxa11GJSAAI= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=amazon.com; spf=pass smtp.mailfrom=amazon.co.jp; dkim=pass (1024-bit key) header.d=amazon.com header.i=@amazon.com header.b=Us/UOrkW; arc=none smtp.client-ip=207.171.188.206 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=amazon.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=amazon.co.jp Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=amazon.com header.i=@amazon.com header.b="Us/UOrkW" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.com; i=@amazon.com; q=dns/txt; s=amazon201209; t=1709928593; x=1741464593; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=QGBgywCWjSg5CboBkrCLLo5S4b/LzTQ1HKQy46bJwCs=; b=Us/UOrkWXXz4fJqprkY4jLRHTAOVbB2kLAPVESn7SEOQOIG9tOosntJd n+V50DGvI36eS/10fUBAhGB5cuGG+4nzWCS4BYj8ME4Xp+iWUsUmlrRX/ kQA0BOpTk74hquKF/ZH0/2jrS+UlHj3Lx2YILthsmqjR/x7s0ubbHLrZ0 U=; X-IronPort-AV: E=Sophos;i="6.07,110,1708387200"; d="scan'208";a="709740712" Received: from pdx4-co-svc-p1-lb2-vlan2.amazon.com (HELO smtpout.prod.us-west-2.prod.farcaster.email.amazon.dev) ([10.25.36.210]) by smtp-border-fw-9106.sea19.amazon.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 08 Mar 2024 20:09:46 +0000 Received: from EX19MTAUWA002.ant.amazon.com [10.0.21.151:48575] by smtpin.naws.us-west-2.prod.farcaster.email.amazon.dev [10.0.56.117:2525] with esmtp (Farcaster) id 1da7a49e-d4b2-41da-bf07-75db711d2a56; Fri, 8 Mar 2024 20:09:45 +0000 (UTC) X-Farcaster-Flow-ID: 1da7a49e-d4b2-41da-bf07-75db711d2a56 Received: from EX19D004ANA001.ant.amazon.com (10.37.240.138) by EX19MTAUWA002.ant.amazon.com (10.250.64.202) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1258.28; Fri, 8 Mar 2024 20:09:41 +0000 Received: from 88665a182662.ant.amazon.com.com (10.142.235.16) by EX19D004ANA001.ant.amazon.com (10.37.240.138) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1258.28; Fri, 8 Mar 2024 20:09:38 +0000 From: Kuniyuki Iwashima To: "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Allison Henderson CC: Kuniyuki Iwashima , Kuniyuki Iwashima , , , Subject: [PATCH v5 net 1/2] tcp: Fix NEW_SYN_RECV handling in inet_twsk_purge() Date: Fri, 8 Mar 2024 12:01:21 -0800 Message-ID: <20240308200122.64357-2-kuniyu@amazon.com> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20240308200122.64357-1-kuniyu@amazon.com> References: <20240308200122.64357-1-kuniyu@amazon.com> Precedence: bulk X-Mailing-List: linux-rdma@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-ClientProxiedBy: EX19D038UWC002.ant.amazon.com (10.13.139.238) To EX19D004ANA001.ant.amazon.com (10.37.240.138) From: Eric Dumazet inet_twsk_purge() uses rcu to find TIME_WAIT and NEW_SYN_RECV objects to purge. These objects use SLAB_TYPESAFE_BY_RCU semantic and need special care. We need to use refcount_inc_not_zero(&sk->sk_refcnt). Reuse the existing correct logic I wrote for TIME_WAIT, because both structures have common locations for sk_state, sk_family, and netns pointer. If after the refcount_inc_not_zero() the object fields longer match the keys, use sock_gen_put(sk) to release the refcount. Then we can call inet_twsk_deschedule_put() for TIME_WAIT, inet_csk_reqsk_queue_drop_and_put() for NEW_SYN_RECV sockets, with BH disabled. Then we need to restart the loop because we had drop rcu_read_lock(). Fixes: 740ea3c4a0b2 ("tcp: Clean up kernel listener's reqsk in inet_twsk_purge()") Link: https://lore.kernel.org/netdev/CANn89iLvFuuihCtt9PME2uS1WJATnf5fKjDToa1WzVnRzHnPfg@mail.gmail.com/T/#u Signed-off-by: Eric Dumazet --- [ Kuniyuki: fixed some checkpatch checks & warnings. ] --- net/ipv4/inet_timewait_sock.c | 41 ++++++++++++++++------------------- 1 file changed, 19 insertions(+), 22 deletions(-) diff --git a/net/ipv4/inet_timewait_sock.c b/net/ipv4/inet_timewait_sock.c index 5befa4de5b24..e8de45d34d56 100644 --- a/net/ipv4/inet_timewait_sock.c +++ b/net/ipv4/inet_timewait_sock.c @@ -263,12 +263,12 @@ void __inet_twsk_schedule(struct inet_timewait_sock *tw, int timeo, bool rearm) } EXPORT_SYMBOL_GPL(__inet_twsk_schedule); +/* Remove all non full sockets (TIME_WAIT and NEW_SYN_RECV) for dead netns */ void inet_twsk_purge(struct inet_hashinfo *hashinfo, int family) { - struct inet_timewait_sock *tw; - struct sock *sk; struct hlist_nulls_node *node; unsigned int slot; + struct sock *sk; for (slot = 0; slot <= hashinfo->ehash_mask; slot++) { struct inet_ehash_bucket *head = &hashinfo->ehash[slot]; @@ -277,38 +277,35 @@ void inet_twsk_purge(struct inet_hashinfo *hashinfo, int family) rcu_read_lock(); restart: sk_nulls_for_each_rcu(sk, node, &head->chain) { - if (sk->sk_state != TCP_TIME_WAIT) { - /* A kernel listener socket might not hold refcnt for net, - * so reqsk_timer_handler() could be fired after net is - * freed. Userspace listener and reqsk never exist here. - */ - if (unlikely(sk->sk_state == TCP_NEW_SYN_RECV && - hashinfo->pernet)) { - struct request_sock *req = inet_reqsk(sk); - - inet_csk_reqsk_queue_drop_and_put(req->rsk_listener, req); - } + int state = inet_sk_state_load(sk); + if ((1 << state) & ~(TCPF_TIME_WAIT | + TCPF_NEW_SYN_RECV)) continue; - } - tw = inet_twsk(sk); - if ((tw->tw_family != family) || - refcount_read(&twsk_net(tw)->ns.count)) + if (sk->sk_family != family || + refcount_read(&sock_net(sk)->ns.count)) continue; - if (unlikely(!refcount_inc_not_zero(&tw->tw_refcnt))) + if (unlikely(!refcount_inc_not_zero(&sk->sk_refcnt))) continue; - if (unlikely((tw->tw_family != family) || - refcount_read(&twsk_net(tw)->ns.count))) { - inet_twsk_put(tw); + if (unlikely(sk->sk_family != family || + refcount_read(&sock_net(sk)->ns.count))) { + sock_gen_put(sk); goto restart; } rcu_read_unlock(); local_bh_disable(); - inet_twsk_deschedule_put(tw); + if (state == TCP_TIME_WAIT) { + inet_twsk_deschedule_put(inet_twsk(sk)); + } else { + struct request_sock *req = inet_reqsk(sk); + + inet_csk_reqsk_queue_drop_and_put(req->rsk_listener, + req); + } local_bh_enable(); goto restart_rcu; } From patchwork Fri Mar 8 20:01:22 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Kuniyuki Iwashima X-Patchwork-Id: 13587237 Received: from smtp-fw-9105.amazon.com (smtp-fw-9105.amazon.com [207.171.188.204]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9C2F15A4C0; Fri, 8 Mar 2024 20:10:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=207.171.188.204 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1709928619; cv=none; b=eIxurF0XFCEtJ9Ov6QGG7AehHZbQ/ZWoimZjxpUim01vkUaZ+1JvmA9ESFRNMpwQ0apfooTjpw9LKjmDu6PNXHb+OmyDr/vHhBo2s1emQF8ziOgdo5ITgkNE8C9lWBIbjoqKbnKpqmpBvYRvH8sMoydOcioN0J+Aqg5GUvv6W0Q= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1709928619; c=relaxed/simple; bh=4WM+wUvnbTHRz2eV4XY6elFPBHAxwoIPaDIQkdWcSrw=; h=From:To:CC:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=BTRSxm++piXI6uVd1yiICy9iSWNKnobKAAj+svpIZ8YuSoJUwoIMwp5aBk0/m4Pj1orwu4TnGtPcAKz8jaHY7sctsCgJyeC/vRQhCBCDCTOuabywvLVbNjtvC7z/6i5LwF1EKySn4QeqEW9VSyTjlSxC2g28i7PBTbDj5YDiM7k= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=amazon.com; spf=pass smtp.mailfrom=amazon.co.jp; dkim=pass (1024-bit key) header.d=amazon.com header.i=@amazon.com header.b=vRMJW4xi; arc=none smtp.client-ip=207.171.188.204 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=amazon.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=amazon.co.jp Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=amazon.com header.i=@amazon.com header.b="vRMJW4xi" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.com; i=@amazon.com; q=dns/txt; s=amazon201209; t=1709928617; x=1741464617; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=U0RPgy773C5+DdQUYA3mfjmJjSMNNGTss/mkPhGk2xE=; b=vRMJW4xiZYyKMi2wrEt95P/ztboDj1MOohkbfuOLy3vhbU110cRFMf2C VrX+c8VDxr7ZPAfxvB0WFLjUqSeL/Ck7seu4OaOSZB1zgwNWBDUsJ8xFq UiQ7N4eKl/Xs9nv2FczEYRcIFfq4O+gB5BKSoxGomCAlmisTddEKHddqM Q=; X-IronPort-AV: E=Sophos;i="6.07,110,1708387200"; d="scan'208";a="710354146" Received: from pdx4-co-svc-p1-lb2-vlan2.amazon.com (HELO smtpout.prod.us-west-2.prod.farcaster.email.amazon.dev) ([10.25.36.210]) by smtp-border-fw-9105.sea19.amazon.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 08 Mar 2024 20:10:12 +0000 Received: from EX19MTAUWA002.ant.amazon.com [10.0.21.151:21956] by smtpin.naws.us-west-2.prod.farcaster.email.amazon.dev [10.0.58.222:2525] with esmtp (Farcaster) id 03e830d6-c8b9-4074-b8d0-6973a7970bc3; Fri, 8 Mar 2024 20:10:11 +0000 (UTC) X-Farcaster-Flow-ID: 03e830d6-c8b9-4074-b8d0-6973a7970bc3 Received: from EX19D004ANA001.ant.amazon.com (10.37.240.138) by EX19MTAUWA002.ant.amazon.com (10.250.64.202) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1258.28; Fri, 8 Mar 2024 20:10:11 +0000 Received: from 88665a182662.ant.amazon.com.com (10.142.235.16) by EX19D004ANA001.ant.amazon.com (10.37.240.138) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1258.28; Fri, 8 Mar 2024 20:10:08 +0000 From: Kuniyuki Iwashima To: "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Allison Henderson CC: Kuniyuki Iwashima , Kuniyuki Iwashima , , , , syzkaller Subject: [PATCH v5 net 2/2] rds: tcp: Fix use-after-free of net in reqsk_timer_handler(). Date: Fri, 8 Mar 2024 12:01:22 -0800 Message-ID: <20240308200122.64357-3-kuniyu@amazon.com> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20240308200122.64357-1-kuniyu@amazon.com> References: <20240308200122.64357-1-kuniyu@amazon.com> Precedence: bulk X-Mailing-List: linux-rdma@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-ClientProxiedBy: EX19D041UWB003.ant.amazon.com (10.13.139.176) To EX19D004ANA001.ant.amazon.com (10.37.240.138) syzkaller reported a warning of netns tracker [0] followed by KASAN splat [1] and another ref tracker warning [1]. syzkaller could not find a repro, but in the log, the only suspicious sequence was as follows: 18:26:22 executing program 1: r0 = socket$inet6_mptcp(0xa, 0x1, 0x106) ... connect$inet6(r0, &(0x7f0000000080)={0xa, 0x4001, 0x0, @loopback}, 0x1c) (async) The notable thing here is 0x4001 in connect(), which is RDS_TCP_PORT. So, the scenario would be: 1. unshare(CLONE_NEWNET) creates a per netns tcp listener in rds_tcp_listen_init(). 2. syz-executor connect()s to it and creates a reqsk. 3. syz-executor exit()s immediately. 4. netns is dismantled. [0] 5. reqsk timer is fired, and UAF happens while freeing reqsk. [1] 6. listener is freed after RCU grace period. [2] Basically, reqsk assumes that the listener guarantees netns safety until all reqsk timers are expired by holding the listener's refcount. However, this was not the case for kernel sockets. Commit 740ea3c4a0b2 ("tcp: Clean up kernel listener's reqsk in inet_twsk_purge()") fixed this issue only for per-netns ehash. Let's apply the same fix for the global ehash. [0]: ref_tracker: net notrefcnt@0000000065449cc3 has 1/1 users at sk_alloc (./include/net/net_namespace.h:337 net/core/sock.c:2146) inet6_create (net/ipv6/af_inet6.c:192 net/ipv6/af_inet6.c:119) __sock_create (net/socket.c:1572) rds_tcp_listen_init (net/rds/tcp_listen.c:279) rds_tcp_init_net (net/rds/tcp.c:577) ops_init (net/core/net_namespace.c:137) setup_net (net/core/net_namespace.c:340) copy_net_ns (net/core/net_namespace.c:497) create_new_namespaces (kernel/nsproxy.c:110) unshare_nsproxy_namespaces (kernel/nsproxy.c:228 (discriminator 4)) ksys_unshare (kernel/fork.c:3429) __x64_sys_unshare (kernel/fork.c:3496) do_syscall_64 (arch/x86/entry/common.c:52 arch/x86/entry/common.c:83) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:129) ... WARNING: CPU: 0 PID: 27 at lib/ref_tracker.c:179 ref_tracker_dir_exit (lib/ref_tracker.c:179) [1]: BUG: KASAN: slab-use-after-free in inet_csk_reqsk_queue_drop (./include/net/inet_hashtables.h:180 net/ipv4/inet_connection_sock.c:952 net/ipv4/inet_connection_sock.c:966) Read of size 8 at addr ffff88801b370400 by task swapper/0/0 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014 Call Trace: dump_stack_lvl (lib/dump_stack.c:107 (discriminator 1)) print_report (mm/kasan/report.c:378 mm/kasan/report.c:488) kasan_report (mm/kasan/report.c:603) inet_csk_reqsk_queue_drop (./include/net/inet_hashtables.h:180 net/ipv4/inet_connection_sock.c:952 net/ipv4/inet_connection_sock.c:966) reqsk_timer_handler (net/ipv4/inet_connection_sock.c:979 net/ipv4/inet_connection_sock.c:1092) call_timer_fn (./arch/x86/include/asm/jump_label.h:27 ./include/linux/jump_label.h:207 ./include/trace/events/timer.h:127 kernel/time/timer.c:1701) __run_timers.part.0 (kernel/time/timer.c:1752 kernel/time/timer.c:2038) run_timer_softirq (kernel/time/timer.c:2053) __do_softirq (./arch/x86/include/asm/jump_label.h:27 ./include/linux/jump_label.h:207 ./include/trace/events/irq.h:142 kernel/softirq.c:554) irq_exit_rcu (kernel/softirq.c:427 kernel/softirq.c:632 kernel/softirq.c:644) sysvec_apic_timer_interrupt (arch/x86/kernel/apic/apic.c:1076 (discriminator 14)) Allocated by task 258 on cpu 0 at 83.612050s: kasan_save_stack (mm/kasan/common.c:48) kasan_save_track (mm/kasan/common.c:68) __kasan_slab_alloc (mm/kasan/common.c:343) kmem_cache_alloc (mm/slub.c:3813 mm/slub.c:3860 mm/slub.c:3867) copy_net_ns (./include/linux/slab.h:701 net/core/net_namespace.c:421 net/core/net_namespace.c:480) create_new_namespaces (kernel/nsproxy.c:110) unshare_nsproxy_namespaces (kernel/nsproxy.c:228 (discriminator 4)) ksys_unshare (kernel/fork.c:3429) __x64_sys_unshare (kernel/fork.c:3496) do_syscall_64 (arch/x86/entry/common.c:52 arch/x86/entry/common.c:83) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:129) Freed by task 27 on cpu 0 at 329.158864s: kasan_save_stack (mm/kasan/common.c:48) kasan_save_track (mm/kasan/common.c:68) kasan_save_free_info (mm/kasan/generic.c:643) __kasan_slab_free (mm/kasan/common.c:265) kmem_cache_free (mm/slub.c:4299 mm/slub.c:4363) cleanup_net (net/core/net_namespace.c:456 net/core/net_namespace.c:446 net/core/net_namespace.c:639) process_one_work (kernel/workqueue.c:2638) worker_thread (kernel/workqueue.c:2700 kernel/workqueue.c:2787) kthread (kernel/kthread.c:388) ret_from_fork (arch/x86/kernel/process.c:153) ret_from_fork_asm (arch/x86/entry/entry_64.S:250) The buggy address belongs to the object at ffff88801b370000 which belongs to the cache net_namespace of size 4352 The buggy address is located 1024 bytes inside of freed 4352-byte region [ffff88801b370000, ffff88801b371100) [2]: WARNING: CPU: 0 PID: 95 at lib/ref_tracker.c:228 ref_tracker_free (lib/ref_tracker.c:228 (discriminator 1)) Modules linked in: Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014 RIP: 0010:ref_tracker_free (lib/ref_tracker.c:228 (discriminator 1)) ... Call Trace: __sk_destruct (./include/net/net_namespace.h:353 net/core/sock.c:2204) rcu_core (./arch/x86/include/asm/preempt.h:26 kernel/rcu/tree.c:2165 kernel/rcu/tree.c:2433) __do_softirq (./arch/x86/include/asm/jump_label.h:27 ./include/linux/jump_label.h:207 ./include/trace/events/irq.h:142 kernel/softirq.c:554) irq_exit_rcu (kernel/softirq.c:427 kernel/softirq.c:632 kernel/softirq.c:644) sysvec_apic_timer_interrupt (arch/x86/kernel/apic/apic.c:1076 (discriminator 14)) Reported-by: syzkaller Suggested-by: Eric Dumazet Fixes: 467fa15356ac ("RDS-TCP: Support multiple RDS-TCP listen endpoints, one per netns.") Signed-off-by: Kuniyuki Iwashima Reviewed-by: Eric Dumazet --- net/ipv4/tcp_minisocks.c | 4 ---- 1 file changed, 4 deletions(-) diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c index 9e85f2a0bddd..0ecc7311dc6c 100644 --- a/net/ipv4/tcp_minisocks.c +++ b/net/ipv4/tcp_minisocks.c @@ -398,10 +398,6 @@ void tcp_twsk_purge(struct list_head *net_exit_list, int family) /* Even if tw_refcount == 1, we must clean up kernel reqsk */ inet_twsk_purge(net->ipv4.tcp_death_row.hashinfo, family); } else if (!purged_once) { - /* The last refcount is decremented in tcp_sk_exit_batch() */ - if (refcount_read(&net->ipv4.tcp_death_row.tw_refcount) == 1) - continue; - inet_twsk_purge(&tcp_hashinfo, family); purged_once = true; }