From: Lorenz Bauer lmb@cloudflare.com
commit 85b8ac01a421791d66c3a458a7f83cfd173fe3fa upstream.
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.
Fixes: 604326b41a6f ("bpf, sockmap: convert to generic sk_msg interface") Signed-off-by: Lorenz Bauer lmb@cloudflare.com Signed-off-by: Daniel Borkmann daniel@iogearbox.net Reviewed-by: Jakub Sitnicki jakub@cloudflare.com Link: https://lore.kernel.org/bpf/20200207103713.28175-1-lmb@cloudflare.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- net/core/sock_map.c | 16 ++++++++++------ 1 file changed, 10 insertions(+), 6 deletions(-)
--- a/net/core/sock_map.c +++ b/net/core/sock_map.c @@ -417,14 +417,16 @@ static int sock_map_update_elem(struct b 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); @@ -740,14 +742,16 @@ static int sock_hash_update_elem(struct 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);