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:
<IRQ>
__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
</IRQ>

Fixes: d1e5e6408b30 ("tcp: Introduce optional per-netns ehash.")
Reported-by: syzbot <syzkaller@googlegroups.com>
Reported-by: Eric Dumazet <edumazet@google.com>
Suggested-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20221012145036.74960-1-kuniyu@amazon.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/ipv4/inet_timewait_sock.c b/net/ipv4/inet_timewait_sock.c
index 71d3bb0..66fc940 100644 (file)
--- 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 79f30f0..c375f60 100644 (file)
--- 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;
                }