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    Subject[PATCH AUTOSEL 5.5 134/542] bpf, sockhash: Synchronize_rcu before free'ing map
    Date
    From: Jakub Sitnicki <jakub@cloudflare.com>

    [ Upstream commit 0b2dc83906cf1e694e48003eae5df8fa63f76fd9 ]

    We need to have a synchronize_rcu before free'ing the sockhash because any
    outstanding psock references will have a pointer to the map and when they
    use it, this could trigger a use after free.

    This is a sister fix for sockhash, following commit 2bb90e5cc90e ("bpf:
    sockmap, synchronize_rcu before free'ing map") which addressed sockmap,
    which comes from a manual audit.

    Fixes: 604326b41a6fb ("bpf, sockmap: convert to generic sk_msg interface")
    Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
    Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
    Acked-by: John Fastabend <john.fastabend@gmail.com>
    Link: https://lore.kernel.org/bpf/20200206111652.694507-3-jakub@cloudflare.com
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    net/core/sock_map.c | 4 ++++
    1 file changed, 4 insertions(+)

    diff --git a/net/core/sock_map.c b/net/core/sock_map.c
    index 8998e356f4232..058422b932607 100644
    --- a/net/core/sock_map.c
    +++ b/net/core/sock_map.c
    @@ -250,6 +250,7 @@ static void sock_map_free(struct bpf_map *map)
    raw_spin_unlock_bh(&stab->lock);
    rcu_read_unlock();

    + /* wait for psock readers accessing its map link */
    synchronize_rcu();

    bpf_map_area_free(stab->sks);
    @@ -873,6 +874,9 @@ static void sock_hash_free(struct bpf_map *map)
    }
    rcu_read_unlock();

    + /* wait for psock readers accessing its map link */
    + synchronize_rcu();
    +
    bpf_map_area_free(htab->buckets);
    kfree(htab);
    }
    --
    2.20.1
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