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Message-ID: <87h6eox4t9.fsf@cloudflare.com>
Date: Thu, 23 May 2024 11:20:34 +0200
From: Jakub Sitnicki <jakub@...udflare.com>
To: Paolo Abeni <pabeni@...hat.com>
Cc: Thadeu Lima de Souza Cascardo <cascardo@...lia.com>,
netdev@...r.kernel.org, Cong Wang <cong.wang@...edance.com>, Eric
Dumazet <edumazet@...gle.com>, Daniel Borkmann <daniel@...earbox.net>,
John Fastabend <john.fastabend@...il.com>, "David S. Miller"
<davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, Alexei
Starovoitov <ast@...nel.org>, bpf@...r.kernel.org,
kernel-dev@...lia.com,
syzbot+07a2e4a1a57118ef7355@...kaller.appspotmail.com,
stable@...r.kernel.org
Subject: Re: [PATCH net] sock_map: avoid race between sock_map_close and
sk_psock_put
On Thu, May 23, 2024 at 09:52 AM +02, Paolo Abeni wrote:
> On Wed, 2024-05-22 at 14:08 +0200, Paolo Abeni wrote:
>> On Mon, 2024-05-20 at 18:41 -0300, Thadeu Lima de Souza Cascardo wrote:
>> > sk_psock_get will return NULL if the refcount of psock has gone to 0, which
>> > will happen when the last call of sk_psock_put is done. However,
>> > sk_psock_drop may not have finished yet, so the close callback will still
>> > point to sock_map_close despite psock being NULL.
>> >
>> > This can be reproduced with a thread deleting an element from the sock map,
>> > while the second one creates a socket, adds it to the map and closes it.
>> >
>> > That will trigger the WARN_ON_ONCE:
>> >
>> > ------------[ cut here ]------------
>> > WARNING: CPU: 1 PID: 7220 at net/core/sock_map.c:1701 sock_map_close+0x2a2/0x2d0 net/core/sock_map.c:1701
>> > Modules linked in:
>> > CPU: 1 PID: 7220 Comm: syz-executor380 Not tainted 6.9.0-syzkaller-07726-g3c999d1ae3c7 #0
>> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/02/2024
>> > RIP: 0010:sock_map_close+0x2a2/0x2d0 net/core/sock_map.c:1701
>> > Code: df e8 92 29 88 f8 48 8b 1b 48 89 d8 48 c1 e8 03 42 80 3c 20 00 74 08 48 89 df e8 79 29 88 f8 4c 8b 23 eb 89 e8 4f 15 23 f8 90 <0f> 0b 90 48 83 c4 08 5b 41 5c 41 5d 41 5e 41 5f 5d e9 13 26 3d 02
>> > RSP: 0018:ffffc9000441fda8 EFLAGS: 00010293
>> > RAX: ffffffff89731ae1 RBX: ffffffff94b87540 RCX: ffff888029470000
>> > RDX: 0000000000000000 RSI: ffffffff8bcab5c0 RDI: ffffffff8c1faba0
>> > RBP: 0000000000000000 R08: ffffffff92f9b61f R09: 1ffffffff25f36c3
>> > R10: dffffc0000000000 R11: fffffbfff25f36c4 R12: ffffffff89731840
>> > R13: ffff88804b587000 R14: ffff88804b587000 R15: ffffffff89731870
>> > FS: 000055555e080380(0000) GS:ffff8880b9500000(0000) knlGS:0000000000000000
>> > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> > CR2: 0000000000000000 CR3: 00000000207d4000 CR4: 0000000000350ef0
>> > Call Trace:
>> > <TASK>
>> > unix_release+0x87/0xc0 net/unix/af_unix.c:1048
>> > __sock_release net/socket.c:659 [inline]
>> > sock_close+0xbe/0x240 net/socket.c:1421
>> > __fput+0x42b/0x8a0 fs/file_table.c:422
>> > __do_sys_close fs/open.c:1556 [inline]
>> > __se_sys_close fs/open.c:1541 [inline]
>> > __x64_sys_close+0x7f/0x110 fs/open.c:1541
>> > do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>> > do_syscall_64+0xf5/0x240 arch/x86/entry/common.c:83
>> > entry_SYSCALL_64_after_hwframe+0x77/0x7f
>> > RIP: 0033:0x7fb37d618070
>> > Code: 00 00 48 c7 c2 b8 ff ff ff f7 d8 64 89 02 b8 ff ff ff ff eb d4 e8 10 2c 00 00 80 3d 31 f0 07 00 00 74 17 b8 03 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 48 c3 0f 1f 80 00 00 00 00 48 83 ec 18 89 7c
>> > RSP: 002b:00007ffcd4a525d8 EFLAGS: 00000202 ORIG_RAX: 0000000000000003
>> > RAX: ffffffffffffffda RBX: 0000000000000005 RCX: 00007fb37d618070
>> > RDX: 0000000000000010 RSI: 00000000200001c0 RDI: 0000000000000004
>> > RBP: 0000000000000000 R08: 0000000100000000 R09: 0000000100000000
>> > R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000000
>> > R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
>> > </TASK>
>> >
>> > Use sk_psock, which will only check that the pointer is not been set to
>> > NULL yet, which should only happen after the callbacks are restored. If,
>> > then, a reference can still be gotten, we may call sk_psock_stop and cancel
>> > psock->work.
>> >
>> > After that change, the reproducer does not trigger the WARN_ON_ONCE
>> > anymore.
>> >
>> > Reported-by: syzbot+07a2e4a1a57118ef7355@...kaller.appspotmail.com
>> > Closes: https://syzkaller.appspot.com/bug?extid=07a2e4a1a57118ef7355
>> > Fixes: aadb2bb83ff7 ("sock_map: Fix a potential use-after-free in sock_map_close()")
>> > Fixes: 5b4a79ba65a1 ("bpf, sockmap: Don't let sock_map_{close,destroy,unhash} call itself")
>> > Cc: stable@...r.kernel.org
>> > Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@...lia.com>
>> > ---
>> > net/core/sock_map.c | 14 +++++++++-----
>> > 1 file changed, 9 insertions(+), 5 deletions(-)
>> >
>> > diff --git a/net/core/sock_map.c b/net/core/sock_map.c
>> > index 9402889840bf..13267e667a4c 100644
>> > --- a/net/core/sock_map.c
>> > +++ b/net/core/sock_map.c
>> > @@ -1680,19 +1680,23 @@ void sock_map_close(struct sock *sk, long timeout)
>> >
>> > lock_sock(sk);
>> > rcu_read_lock();
>> > - psock = sk_psock_get(sk);
>> > + psock = sk_psock(sk);
>> > if (unlikely(!psock)) {
>> > + saved_close = READ_ONCE(sk->sk_prot)->close;
>> > rcu_read_unlock();
>> > release_sock(sk);
>> > - saved_close = READ_ONCE(sk->sk_prot)->close;
>> > } else {
>> > saved_close = psock->saved_close;
>> > sock_map_remove_links(sk, psock);
>> > + psock = sk_psock_get(sk);
>> > rcu_read_unlock();
>> > - sk_psock_stop(psock);
>> > + if (psock)
>> > + sk_psock_stop(psock);
>> > release_sock(sk);
>> > - cancel_delayed_work_sync(&psock->work);
>> > - sk_psock_put(sk, psock);
>> > + if (psock) {
>> > + cancel_delayed_work_sync(&psock->work);
>> > + sk_psock_put(sk, psock);
>> > + }
>> > }
>> >
>> > /* Make sure we do not recurse. This is a bug.
>>
>> As a personal opinion I think the code will become simple reordering
>> the condition, something alike:
>>
>> if (psock) {
>> saved_close = psock->saved_close;
>> sock_map_remove_links(sk, psock);
>> psock = sk_psock_get(sk);
>> if (!psock)
>> goto no_psock;
>> rcu_read_unlock();
>> sk_psock_stop(psock);
>> release_sock(sk);
>> cancel_delayed_work_sync(&psock->work);
>> sk_psock_put(sk, psock);
>> } else {
>> no_psock:
>> saved_close = READ_ONCE(sk->sk_prot)->close;
>
> FTR, the above is wrong, should be:
>
> saved_close = READ_ONCE(sk->sk_prot)->close;
> no_psock:
>
>> rcu_read_unlock();
>> release_sock(sk);
>> }
>
> /P
Paolo's version does read better to me as well.
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