It's currently possible to insert sockets in unexpected states into
a sockmap, due to a TOCTTOU when updating the map from a syscall.
sock_map_update_elem checks that sk->sk_state == TCP_ESTABLISHED,
locks the socket and then calls sock_map_update_common. At this
point, the socket may have transitioned into another state, and
the earlier assumptions don't hold anymore. Crucially, it's
conceivable (though very unlikely) that a socket has become unhashed.
This breaks the sockmap's assumption that it will get a callback
via sk->sk_prot->unhash.
Fix this by checking the (fixed) sk_type and sk_protocol without the
lock, followed by a locked check of sk_state.
Unfortunately it's not possible to push the check down into
sock_(map|hash)_update_common, since BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB
run before the socket has transitioned from TCP_SYN_RECV into
TCP_ESTABLISHED.
Signed-off-by: Lorenz Bauer <lmb@xxxxxxxxxxxxxx>
Fixes: 604326b41a6f ("bpf, sockmap: convert to generic sk_msg interface")
---
net/core/sock_map.c | 16 ++++++++++------
1 file changed, 10 insertions(+), 6 deletions(-)
diff --git a/net/core/sock_map.c b/net/core/sock_map.c
index 8998e356f423..36a2433e183f 100644
--- a/net/core/sock_map.c
+++ b/net/core/sock_map.c
@@ -416,14 +416,16 @@ static int sock_map_update_elem(struct bpf_map *map, void *key,
ret = -EINVAL;
goto out;
}
- if (!sock_map_sk_is_suitable(sk) ||
- sk->sk_state != TCP_ESTABLISHED) {
+ if (!sock_map_sk_is_suitable(sk)) {
ret = -EOPNOTSUPP;
goto out;
}
sock_map_sk_acquire(sk);
- ret = sock_map_update_common(map, idx, sk, flags);
+ if (sk->sk_state != TCP_ESTABLISHED)
+ ret = -EOPNOTSUPP;
+ else
+ ret = sock_map_update_common(map, idx, sk, flags);
sock_map_sk_release(sk);
out:
fput(sock->file);
@@ -739,14 +741,16 @@ static int sock_hash_update_elem(struct bpf_map *map, void *key,
ret = -EINVAL;
goto out;
}
- if (!sock_map_sk_is_suitable(sk) ||
- sk->sk_state != TCP_ESTABLISHED) {
+ if (!sock_map_sk_is_suitable(sk)) {
ret = -EOPNOTSUPP;
goto out;
}
sock_map_sk_acquire(sk);
- ret = sock_hash_update_common(map, key, sk, flags);
+ if (sk->sk_state != TCP_ESTABLISHED)
+ ret = -EOPNOTSUPP;
+ else
+ ret = sock_hash_update_common(map, key, sk, flags);
sock_map_sk_release(sk);
out:
fput(sock->file);
--
2.20.1
