[PATCH bpf 1/2] bpf: sockmap, fix introduced strparser recursive lock

John Fastabend
2024-06-25T20:16:35Z

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@datadoghq.com>
Signed-off-by: John Fastabend <john.fastabend@gmail.com>
---
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;
}

--
2.33.0