netdev - [bpf PATCH v2 2/8] bpf: sockmap, ensure sock lock held during tear down

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Date:   Sat, 11 Jan 2020 06:12:00 +0000
From:   John Fastabend <john.fastabend@...il.com>
To:     bpf@...r.kernel.org
Cc:     netdev@...r.kernel.org, daniel@...earbox.net, ast@...nel.org,
        john.fastabend@...il.com, song@...nel.org, jonathan.lemon@...il.com
Subject: [bpf PATCH v2 2/8] bpf: sockmap, ensure sock lock held during tear down

The sock_map_free() and sock_hash_free() paths used to delete sockmap
and sockhash maps walk the maps and destroy psock and bpf state associated
with the socks in the map. When done the socks no longer have BPF programs
attached and will function normally. This can happen while the socks in
the map are still "live" meaning data may be sent/received during the walk.

Currently, though we don't take the sock_lock when the psock and bpf state
is removed through this path. Specifically, this means we can be writing
into the ops structure pointers such as sendmsg, sendpage, recvmsg, etc.
while they are also being called from the networking side. This is not
safe, we never used proper READ_ONCE/WRITE_ONCE semantics here if we
believed it was safe. Further its not clear to me its even a good idea
to try and do this on "live" sockets while networking side might also
be using the socket. Instead of trying to reason about using the socks
from both sides lets realize that every use case I'm aware of rarely
deletes maps, in fact kubernetes/Cilium case builds map at init and
never tears it down except on errors. So lets do the simple fix and
grab sock lock.

This patch wraps sock deletes from maps in sock lock and adds some
annotations so we catch any other cases easier.

Fixes: 604326b41a6fb ("bpf, sockmap: convert to generic sk_msg interface")
Cc: stable@...r.kernel.org
Acked-by: Song Liu <songliubraving@...com>
Signed-off-by: John Fastabend <john.fastabend@...il.com>
---
 net/core/skmsg.c    | 2 ++
 net/core/sock_map.c | 7 ++++++-
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/net/core/skmsg.c b/net/core/skmsg.c
index ded2d5227678..3866d7e20c07 100644
--- a/net/core/skmsg.c
+++ b/net/core/skmsg.c
@@ -594,6 +594,8 @@ EXPORT_SYMBOL_GPL(sk_psock_destroy);

 void sk_psock_drop(struct sock *sk, struct sk_psock *psock)
 {
+	sock_owned_by_me(sk);
+
 	sk_psock_cork_free(psock);
 	sk_psock_zap_ingress(psock);

diff --git a/net/core/sock_map.c b/net/core/sock_map.c
index eb114ee419b6..8998e356f423 100644
--- a/net/core/sock_map.c
+++ b/net/core/sock_map.c
@@ -241,8 +241,11 @@ static void sock_map_free(struct bpf_map *map)
 		struct sock *sk;

 		sk = xchg(psk, NULL);
-		if (sk)
+		if (sk) {
+			lock_sock(sk);
 			sock_map_unref(sk, psk);
+			release_sock(sk);
+		}
 	}
 	raw_spin_unlock_bh(&stab->lock);
 	rcu_read_unlock();
@@ -862,7 +865,9 @@ static void sock_hash_free(struct bpf_map *map)
 		raw_spin_lock_bh(&bucket->lock);
 		hlist_for_each_entry_safe(elem, node, &bucket->head, node) {
 			hlist_del_rcu(&elem->node);
+			lock_sock(elem->sk);
 			sock_map_unref(elem->sk, elem);
+			release_sock(elem->sk);
 		}
 		raw_spin_unlock_bh(&bucket->lock);
 	}
-- 
2.17.1