netdev - [PATCH net v2 0/2] net: fix issues when uncloning an skb dst+metadata

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Message-Id: <20220207171319.157775-1-atenart@kernel.org>
Date:   Mon,  7 Feb 2022 18:13:17 +0100
From:   Antoine Tenart <atenart@...nel.org>
To:     davem@...emloft.net, kuba@...nel.org
Cc:     Antoine Tenart <atenart@...nel.org>, netdev@...r.kernel.org,
        vladbu@...dia.com, pabeni@...hat.com, pshelar@....org,
        daniel@...earbox.net
Subject: [PATCH net v2 0/2] net: fix issues when uncloning an skb dst+metadata

Hi,

This fixes two issues when uncloning an skb dst+metadata in
tun_dst_unclone; this was initially reported by Vlad Buslov[1]. Because
of the memory leak fixed by patch 2, the issue in patch 1 never happened
in practice.

tun_dst_unclone is called from two different places, one in geneve/vxlan
to handle PMTU and one in net/openvswitch/actions.c where it is used to
retrieve tunnel information. While both Vlad and I tested the former, we
could not for the latter. I did spend quite some time trying to, but
that code path is not easy to trigger. Code inspection shows this should
be fine, the tunnel information (dst+metadata) is uncloned and the skb
it is referenced from is only consumed after all accesses to the tunnel
information are done:

  do_execute_actions
    output_userspace
      dev_fill_metadata_dst         <- dst+metadata is uncloned
      ovs_dp_upcall
        queue_userspace_packet
          ovs_nla_put_tunnel_info   <- metadata (tunnel info) is accessed
    consume_skb                     <- dst+metadata is freed

Since v1:
- Only allocate a dst cache if there is one already.
- Use metadata_dst_free in the dst_cache_init error path. This is OK as
  the dst_cache is zeroed on error.
- Protect the ret variable definition with CONFIG_DST_CACHE.
- Kept Vlad's Tested-by as the changes are minor.

Thanks!
Antoine

Antoine Tenart (2):
  net: do not keep the dst cache when uncloning an skb dst and its
    metadata
  net: fix a memleak when uncloning an skb dst and its metadata

 include/net/dst_metadata.h | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

-- 
2.34.1