Re: [Patch bpf v2] skmsg: check sk_rcvbuf limit before queuing to ingress_skb

Jakub Sitnicki wrote:

On Thu, Jul 01, 2021 at 08:16 AM CEST, Cong Wang wrote:

quoted

From: Cong Wang <redacted>

Jiang observed OOM frequently when testing our AF_UNIX/UDP
proxy. This is due to the fact that we do not actually limit
the socket memory before queueing skb to ingress_skb. We
charge the skb memory later when handling the psock backlog,
but it is not limited either.

This patch adds checks for sk->sk_rcvbuf right before queuing
to ingress_skb and drops packets if this limit exceeds. This
is very similar to UDP receive path. Ideally we should set the
skb owner before this check too, but it is hard to make TCP
happy about sk_forward_alloc.

Reported-by: Jiang Wang <redacted>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: John Fastabend <john.fastabend@gmail.com>
Cc: Lorenz Bauer <redacted>
Cc: Jakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: Cong Wang <redacted>
---

Acked-by: Jakub Sitnicki <jakub@cloudflare.com>

By saying that it is hard to make TCP happy about sk_forward_alloc, I'm
guessing you're referring to problems described in 144748eb0c44 ("bpf,
sockmap: Fix incorrect fwd_alloc accounting") [1]?

I have a couple fixes on my stack here I'm testing that clean up
the tear down logic. Once thats in place maybe its as simple
as adding the owner_r bits and calling the destructor to ensure
memory accounting happens earlier so these ingress_skb packets
are accounted for.

I'll flush those out today, maybe it will be clear then.

Thanks for the fix.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=144748eb0c445091466c9b741ebd0bfcc5914f3d

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