Jakub Sitnicki wrote: > On Tue, Jun 25, 2024 at 01:16 PM -07, John Fastabend wrote: > > Originally there was a race where removing a psock from the sock map while > > it was also receiving an skb and calling sk_psock_data_ready(). It was > > possible the removal code would NULL/set the data_ready callback while > > concurrently calling the hook from receive path. The fix was to wrap the > > access in sk_callback_lock to ensure the saved_data_ready pointer didn't > > change under us. There was some discussion around doing a larger change > > to ensure we could use READ_ONCE/WRITE_ONCE over the callback, but that > > was for *next kernels not stable fixes. > > > > But, we unfortunately introduced a regression with the fix because there > > is another path into this code (that didn't have a test case) through > > the stream parser. The stream parser runs with the lower lock which means > > we get the following splat and lock up. > > > > > > ============================================ > > WARNING: possible recursive locking detected > > 6.10.0-rc2 #59 Not tainted > > -------------------------------------------- > > test_sockmap/342 is trying to acquire lock: > > ffff888007a87228 (clock-AF_INET){++--}-{2:2}, at: > > sk_psock_skb_ingress_enqueue (./include/linux/skmsg.h:467 > > net/core/skmsg.c:555) > > > > but task is already holding lock: > > ffff888007a87228 (clock-AF_INET){++--}-{2:2}, at: > > sk_psock_strp_data_ready (net/core/skmsg.c:1120) > > > > To fix ensure we do not grap lock when we reach this code through the > > strparser. > > > > Fixes: 6648e613226e1 ("bpf, skmsg: Fix NULL pointer dereference in sk_psock_skb_ingress_enqueue") > > Reported-by: Vincent Whitchurch <vincent.whitchurch@xxxxxxxxxxxxx> > > Signed-off-by: John Fastabend <john.fastabend@xxxxxxxxx> > > --- > > include/linux/skmsg.h | 9 +++++++-- > > net/core/skmsg.c | 5 ++++- > > 2 files changed, 11 insertions(+), 3 deletions(-) > > > > diff --git a/include/linux/skmsg.h b/include/linux/skmsg.h > > index c9efda9df285..3659e9b514d0 100644 > > --- a/include/linux/skmsg.h > > +++ b/include/linux/skmsg.h > > @@ -461,13 +461,18 @@ static inline void sk_psock_put(struct sock *sk, struct sk_psock *psock) > > sk_psock_drop(sk, psock); > > } > > > > -static inline void sk_psock_data_ready(struct sock *sk, struct sk_psock *psock) > > +static inline void __sk_psock_data_ready(struct sock *sk, struct sk_psock *psock) > > { > > - read_lock_bh(&sk->sk_callback_lock); > > if (psock->saved_data_ready) > > psock->saved_data_ready(sk); > > else > > sk->sk_data_ready(sk); > > +} > > + > > +static inline void sk_psock_data_ready(struct sock *sk, struct sk_psock *psock) > > +{ > > + read_lock_bh(&sk->sk_callback_lock); > > + __sk_psock_data_ready(sk, psock); > > read_unlock_bh(&sk->sk_callback_lock); > > } > > > > diff --git a/net/core/skmsg.c b/net/core/skmsg.c > > index fd20aae30be2..8429daecbbb6 100644 > > --- a/net/core/skmsg.c > > +++ b/net/core/skmsg.c > > @@ -552,7 +552,10 @@ static int sk_psock_skb_ingress_enqueue(struct sk_buff *skb, > > msg->skb = skb; > > > > sk_psock_queue_msg(psock, msg); > > - sk_psock_data_ready(sk, psock); > > + if (skb_bpf_strparser(skb)) > > + __sk_psock_data_ready(sk, psock); > > + else > > + sk_psock_data_ready(sk, psock); > > return copied; > > } > > If I follow, this is the call chain that leads to the recursive lock: > > sock::sk_data_ready → sk_psock_strp_data_ready > write_lock_bh(&sk->sk_callback_lock) > strp_data_ready > strp_read_sock > proto_ops::read_sock → tcp_read_sock > strp_recv > __strp_recv > strp_callbacks::rcv_msg → sk_psock_strp_read > sk_psock_verdict_apply(verdict=__SK_PASS) > sk_psock_skb_ingress_self > sk_psock_skb_ingress_enqueue > sk_psock_data_ready > read_lock_bh(&sk->sk_callback_lock) !!! > > What I don't get, though, is why strp_data_ready has to be called with a > _writer_ lock? Maybe that should just be a reader lock, and then it can > be recursive. Agree read lock should be fine we just want to ensure the strp is not changing during the callchain there. Let me do that fix instead.