From 740ea3c4a0b2e326b23d7cdf05472a0e92aa39bc Mon Sep 17 00:00:00 2001 From: Kuniyuki Iwashima Date: Wed, 12 Oct 2022 07:50:36 -0700 Subject: [PATCH] tcp: Clean up kernel listener's reqsk in inet_twsk_purge() Eric Dumazet reported a use-after-free related to the per-netns ehash series. [0] When we create a TCP socket from userspace, the socket always holds a refcnt of the netns. This guarantees that a reqsk timer is always fired before netns dismantle. Each reqsk has a refcnt of its listener, so the listener is not freed before the reqsk, and the net is not freed before the listener as well. OTOH, when in-kernel users create a TCP socket, it might not hold a refcnt of its netns. Thus, a reqsk timer can be fired after the netns dismantle and access freed per-netns ehash. To avoid the use-after-free, we need to clean up TCP_NEW_SYN_RECV sockets in inet_twsk_purge() if the netns uses a per-netns ehash. [0]: https://lore.kernel.org/netdev/CANn89iLXMup0dRD_Ov79Xt8N9FM0XdhCHEN05sf3eLwxKweM6w@mail.gmail.com/ BUG: KASAN: use-after-free in tcp_or_dccp_get_hashinfo include/net/inet_hashtables.h:181 [inline] BUG: KASAN: use-after-free in reqsk_queue_unlink+0x320/0x350 net/ipv4/inet_connection_sock.c:913 Read of size 8 at addr ffff88807545bd80 by task syz-executor.2/8301 CPU: 1 PID: 8301 Comm: syz-executor.2 Not tainted 6.0.0-syzkaller-02757-gaf7d23f9d96a #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/22/2022 Call Trace: __dump_stack lib/dump_stack.c:88 [inline] dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106 print_address_description mm/kasan/report.c:317 [inline] print_report.cold+0x2ba/0x719 mm/kasan/report.c:433 kasan_report+0xb1/0x1e0 mm/kasan/report.c:495 tcp_or_dccp_get_hashinfo include/net/inet_hashtables.h:181 [inline] reqsk_queue_unlink+0x320/0x350 net/ipv4/inet_connection_sock.c:913 inet_csk_reqsk_queue_drop net/ipv4/inet_connection_sock.c:927 [inline] inet_csk_reqsk_queue_drop_and_put net/ipv4/inet_connection_sock.c:939 [inline] reqsk_timer_handler+0x724/0x1160 net/ipv4/inet_connection_sock.c:1053 call_timer_fn+0x1a0/0x6b0 kernel/time/timer.c:1474 expire_timers kernel/time/timer.c:1519 [inline] __run_timers.part.0+0x674/0xa80 kernel/time/timer.c:1790 __run_timers kernel/time/timer.c:1768 [inline] run_timer_softirq+0xb3/0x1d0 kernel/time/timer.c:1803 __do_softirq+0x1d0/0x9c8 kernel/softirq.c:571 invoke_softirq kernel/softirq.c:445 [inline] __irq_exit_rcu+0x123/0x180 kernel/softirq.c:650 irq_exit_rcu+0x5/0x20 kernel/softirq.c:662 sysvec_apic_timer_interrupt+0x93/0xc0 arch/x86/kernel/apic/apic.c:1107 Fixes: d1e5e6408b30 ("tcp: Introduce optional per-netns ehash.") Reported-by: syzbot Reported-by: Eric Dumazet Suggested-by: Eric Dumazet Signed-off-by: Kuniyuki Iwashima Reviewed-by: Eric Dumazet Link: https://lore.kernel.org/r/20221012145036.74960-1-kuniyu@amazon.com Signed-off-by: Jakub Kicinski --- net/ipv4/inet_timewait_sock.c | 15 ++++++++++++++- net/ipv4/tcp_minisocks.c | 9 +++++---- 2 files changed, 19 insertions(+), 5 deletions(-) diff --git a/net/ipv4/inet_timewait_sock.c b/net/ipv4/inet_timewait_sock.c index 71d3bb0abf6c..66fc940f9521 100644 --- a/net/ipv4/inet_timewait_sock.c +++ b/net/ipv4/inet_timewait_sock.c @@ -268,8 +268,21 @@ restart_rcu: rcu_read_lock(); restart: sk_nulls_for_each_rcu(sk, node, &head->chain) { - if (sk->sk_state != TCP_TIME_WAIT) + 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); + } + continue; + } + tw = inet_twsk(sk); if ((tw->tw_family != family) || refcount_read(&twsk_net(tw)->ns.count)) diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c index 79f30f026d89..c375f603a16c 100644 --- a/net/ipv4/tcp_minisocks.c +++ b/net/ipv4/tcp_minisocks.c @@ -353,13 +353,14 @@ void tcp_twsk_purge(struct list_head *net_exit_list, int family) struct net *net; list_for_each_entry(net, net_exit_list, exit_list) { - /* The last refcount is decremented in tcp_sk_exit_batch() */ - if (refcount_read(&net->ipv4.tcp_death_row.tw_refcount) == 1) - continue; - if (net->ipv4.tcp_death_row.hashinfo->pernet) { + /* 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; }