netdev - [bpf PATCH v2 0/3] Sockmap RCU splat fix

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Date:   Thu, 25 Jun 2020 16:12:38 -0700
From:   John Fastabend <john.fastabend@...il.com>
To:     kafai@...com, jakub@...udflare.com, daniel@...earbox.net,
        ast@...nel.org
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org,
        john.fastabend@...il.com
Subject: [bpf PATCH v2 0/3] Sockmap RCU splat fix 

Fix a splat introduced by recent changes to avoid skipping ingress policy
when kTLS is enabled. The RCU splat was introduced because in the non-TLS
case the caller is wrapped in an rcu_read_lock/unlock. But, in the TLS
case we have a reference to the psock and the caller did not wrap its
call in rcu_read_lock/unlock.

To fix extend the RCU section to include the redirect case which was
missed. From v1->v2 I changed the location a bit to simplify the code
some. See patch 1.

But, then Martin asked why it was not needed in the non-TLS case. The
answer for patch 1 was, as stated above, because the caller has the
rcu read lock. However, there was still a missing case where a BPF
user could in-theory line up a set of parameters to hit a case
where the code was entered from strparser side from a different context
then the initial caller. To hit this user would need a parser program
to return value greater than skb->len then an ENOMEM error could happen
in the strparser codepath triggering strparser to retry from a workqueue
and without rcu_read_lock original caller used. See patch 2 for details.

Finally, we don't actually have any selftests for parser returning a
value geater than skb->len so add one in patch 3. This is especially
needed because at least I don't have any code that uses the parser
to return value greater than skb->len. So I wouldn't have caught any
errors here in my own testing.

Thanks, John

v1->v2: simplify code in patch 1 some and add patches 2 and 3.

---

John Fastabend (3):
      bpf, sockmap: RCU splat with redirect and strparser error or TLS
      bpf, sockmap: RCU dereferenced psock may be used outside RCU block
      bpf, sockmap: Add ingres skb tests that utilize merge skbs

 net/core/skmsg.c                                   |   23 +++++++++++++-------
 .../selftests/bpf/progs/test_sockmap_kern.h        |    8 ++++++-
 tools/testing/selftests/bpf/test_sockmap.c         |   18 ++++++++++++++++
 3 files changed, 40 insertions(+), 9 deletions(-)

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