Netdev Archive on
help / color / mirror / Atom feed
From: Yonghong Song <>
To: Lorenz Bauer <>, <>,
	<>, Alexei Starovoitov <>,
	Daniel Borkmann <>,
	"David S. Miller" <>,
	Jakub Kicinski <>
Cc: <>, <>,
	<>, <>
Subject: Re: [PATCH bpf-next v3 5/6] bpf: sockmap: allow update from BPF
Date: Fri, 21 Aug 2020 08:47:54 -0700	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On 8/21/20 3:29 AM, Lorenz Bauer wrote:
> Allow calling bpf_map_update_elem on sockmap and sockhash from a BPF
> context. The synchronization required for this is a bit fiddly: we
> need to prevent the socket from changing its state while we add it
> to the sockmap, since we rely on getting a callback via
> sk_prot->unhash. However, we can't just lock_sock like in
> sock_map_sk_acquire because that might sleep. So instead we disable
> softirq processing and use bh_lock_sock to prevent further
> modification.
> Yet, this is still not enough. BPF can be called in contexts where
> the current CPU might have locked a socket. If the BPF can get
> a hold of such a socket, inserting it into a sockmap would lead to
> a deadlock. One straight forward example are sock_ops programs that
> have ctx->sk, but the same problem exists for kprobes, etc.
> We deal with this by allowing sockmap updates only from known safe
> contexts. Improper usage is rejected by the verifier.
> I've audited the enabled contexts to make sure they can't run in
> a locked context. It's possible that CGROUP_SKB and others are
> safe as well, but the auditing here is much more difficult. In
> any case, we can extend the safe contexts when the need arises.
> Signed-off-by: Lorenz Bauer <>

Acked-by: Yonghong Song <>

  reply	other threads:[~2020-08-21 15:48 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-21 10:29 [PATCH bpf-next v3 0/6] Allow updating sockmap / sockhash " Lorenz Bauer
2020-08-21 10:29 ` [PATCH bpf-next v3 1/6] net: sk_msg: simplify sk_psock initialization Lorenz Bauer
2020-08-21 10:29 ` [PATCH bpf-next v3 2/6] bpf: sockmap: merge sockmap and sockhash update functions Lorenz Bauer
2020-08-21 10:29 ` [PATCH bpf-next v3 3/6] bpf: sockmap: call sock_map_update_elem directly Lorenz Bauer
2020-08-21 10:29 ` [PATCH bpf-next v3 4/6] bpf: override the meaning of ARG_PTR_TO_MAP_VALUE for sockmap and sockhash Lorenz Bauer
2020-08-21 15:46   ` Yonghong Song
2020-08-21 10:29 ` [PATCH bpf-next v3 5/6] bpf: sockmap: allow update from BPF Lorenz Bauer
2020-08-21 15:47   ` Yonghong Song [this message]
2020-08-21 10:29 ` [PATCH bpf-next v3 6/6] selftests: bpf: test sockmap " Lorenz Bauer
2020-08-21 16:13   ` Yonghong Song
2020-08-21 22:23 ` [PATCH bpf-next v3 0/6] Allow updating sockmap / sockhash " Alexei Starovoitov

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \ \ \ \ \ \ \ \ \ \ \ \ \ \
    --subject='Re: [PATCH bpf-next v3 5/6] bpf: sockmap: allow update from BPF' \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).