bpf: net: Avoid incorrect bpf_sk_reuseport_detach call

bpf_sk_reuseport_detach is currently called when sk->sk_user_data
is not NULL.  It is incorrect because sk->sk_user_data may not be
managed by the bpf's reuseport_array.  It has been reported in [1] that,
the bpf_sk_reuseport_detach() which is called from udp_lib_unhash() has
corrupted the sk_user_data managed by l2tp.

This patch solves it by using another bit (defined as SK_USER_DATA_BPF)
of the sk_user_data pointer value.  It marks that a sk_user_data is
managed/owned by BPF.

The patch depends on a PTRMASK introduced in
commit f1ff5ce2cd5e ("net, sk_msg: Clear sk_user_data pointer on clone if tagged").

[ Note: sk->sk_user_data is used by bpf's reuseport_array only when a sk is
  added to the bpf's reuseport_array.
  i.e. doing setsockopt(SO_REUSEPORT) and having "sk->sk_reuseport == 1"
  alone will not stop sk->sk_user_data being used by other means. ]

[1]: https://lore.kernel.org/netdev/20200706121259.GA20199@katalix.com/

Fixes: 5dc4c4b7d4e8 ("bpf: Introduce BPF_MAP_TYPE_REUSEPORT_SOCKARRAY")
Reported-by: James Chapman <jchapman@katalix.com>
Reported-by: syzbot+9f092552ba9a5efca5df@syzkaller.appspotmail.com
Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Tested-by: James Chapman <jchapman@katalix.com>
Acked-by: James Chapman <jchapman@katalix.com>
Link: https://lore.kernel.org/bpf/20200709061110.4019316-1-kafai@fb.com

diff --git a/include/net/sock.h b/include/net/sock.h
index 3428619..1183507 100644 (file)
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -533,7 +533,8 @@ enum sk_pacing {
  * be copied.
  */
 #define SK_USER_DATA_NOCOPY    1UL
-#define SK_USER_DATA_PTRMASK   ~(SK_USER_DATA_NOCOPY)
+#define SK_USER_DATA_BPF       2UL     /* Managed by BPF */
+#define SK_USER_DATA_PTRMASK   ~(SK_USER_DATA_NOCOPY | SK_USER_DATA_BPF)
 
 /**
  * sk_user_data_is_nocopy - Test if sk_user_data pointer must not be copied

diff --git a/kernel/bpf/reuseport_array.c b/kernel/bpf/reuseport_array.c
index a95bc8d..cae9d50 100644 (file)
--- a/kernel/bpf/reuseport_array.c
+++ b/kernel/bpf/reuseport_array.c
@@ -24,7 +24,7 @@ void bpf_sk_reuseport_detach(struct sock *sk)
 
        write_lock_bh(&sk->sk_callback_lock);
        sk_user_data = (uintptr_t)sk->sk_user_data;
-       if (sk_user_data) {
+       if (sk_user_data & SK_USER_DATA_BPF) {
                struct sock __rcu **socks;
 
                socks = (void *)(sk_user_data & SK_USER_DATA_PTRMASK);
@@ -309,7 +309,8 @@ int bpf_fd_reuseport_array_update_elem(struct bpf_map *map, void *key,
        if (err)
                goto put_file_unlock;
 
-       sk_user_data = (uintptr_t)&array->ptrs[index] | SK_USER_DATA_NOCOPY;
+       sk_user_data = (uintptr_t)&array->ptrs[index] | SK_USER_DATA_NOCOPY |
+               SK_USER_DATA_BPF;
        WRITE_ONCE(nsk->sk_user_data, (void *)sk_user_data);
        rcu_assign_pointer(array->ptrs[index], nsk);
        free_osk = osk;