net: do not keep the dst cache when uncloning an skb dst and its metadata

stable inclusion
from stable-v5.10.101
commit 2e9fd2d0f69e4cc82a9a497bb14c1d70e75cc430
bugzilla: https://gitee.com/openeuler/kernel/issues/I5669Z

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2e9fd2d0f69e4cc82a9a497bb14c1d70e75cc430



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[ Upstream commit cfc56f85 ]

When uncloning an skb dst and its associated metadata a new dst+metadata
is allocated and the tunnel information from the old metadata is copied
over there.

The issue is the tunnel metadata has references to cached dst, which are
copied along the way. When a dst+metadata refcount drops to 0 the
metadata is freed including the cached dst entries. As they are also
referenced in the initial dst+metadata, this ends up in UaFs.

In practice the above did not happen because of another issue, the
dst+metadata was never freed because its refcount never dropped to 0
(this will be fixed in a subsequent patch).

Fix this by initializing the dst cache after copying the tunnel
information from the old metadata to also unshare the dst cache.

Fixes: d71785ff ("net: add dst_cache to ovs vxlan lwtunnel")
Cc: Paolo Abeni <pabeni@redhat.com>
Reported-by: Vlad Buslov <vladbu@nvidia.com>
Tested-by: Vlad Buslov <vladbu@nvidia.com>
Signed-off-by: Antoine Tenart <atenart@kernel.org>
Acked-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Yu Liao <liaoyu15@huawei.com>
Reviewed-by: Wei Li <liwei391@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>