[PATCH net 2/4] net: proper check if we hold the socket lock during dereference

[Hannes Frederic Sowa]

lockdep_sock_is_held makes sure that we currently own the
lock. sock_owned_by_user simply checks if a user holds the socket. This
could lead to non deterministic lock checks.

Reported-by: Sasha Levin <sasha.le...@oracle.com>
Cc: Daniel Borkmann <dan...@iogearbox.net>
Cc: Alexei Starovoitov <alexei.starovoi...@gmail.com>
Cc: Michal Kubecek <mkube...@suse.cz>
Signed-off-by: Hannes Frederic Sowa <han...@stressinduktion.org>
---
 include/net/sock.h | 5 +++++
 net/core/filter.c  | 6 +++---
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/include/net/sock.h b/include/net/sock.h
index 255d3e03727b73..30f9b5ad0a82ef 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1382,6 +1382,11 @@ static inline void unlock_sock_fast(struct sock *sk, 
bool slow)
                spin_unlock_bh(&sk->sk_lock.slock);
 }
 
+static bool lockdep_sock_is_held(struct sock *sk)
+{
+       return lockdep_is_held(&sk->sk_lock) ||
+              lockdep_is_held(&sk->sk_lock.slock);
+}
 
 struct sock *sk_alloc(struct net *net, int family, gfp_t priority,
                      struct proto *prot, int kern);
diff --git a/net/core/filter.c b/net/core/filter.c
index 4b81b71171b4ce..e8486ba601eae7 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -1166,7 +1166,7 @@ static int __sk_attach_prog(struct bpf_prog *prog, struct 
sock *sk)
        }
 
        old_fp = rcu_dereference_protected(sk->sk_filter,
-                                          sock_owned_by_user(sk));
+                                          lockdep_sock_is_held(sk));
        rcu_assign_pointer(sk->sk_filter, fp);
 
        if (old_fp)
@@ -2259,7 +2259,7 @@ int sk_detach_filter(struct sock *sk)
                return -EPERM;
 
        filter = rcu_dereference_protected(sk->sk_filter,
-                                          sock_owned_by_user(sk));
+                                          lockdep_sock_is_held(sk));
        if (filter) {
                RCU_INIT_POINTER(sk->sk_filter, NULL);
                sk_filter_uncharge(sk, filter);
@@ -2279,7 +2279,7 @@ int sk_get_filter(struct sock *sk, struct sock_filter 
__user *ubuf,
 
        lock_sock(sk);
        filter = rcu_dereference_protected(sk->sk_filter,
-                                          sock_owned_by_user(sk));
+                                          lockdep_sock_is_held(sk));
        if (!filter)
                goto out;
 
-- 
2.5.5