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    Subject[PATCH 4.4 26/58] tcp: md5: add missing memory barriers in tcp_md5_do_add()/tcp_md5_hash_key()
    Date
    From: Eric Dumazet <edumazet@google.com>

    [ Upstream commit 6a2febec338df7e7699a52d00b2e1207dcf65b28 ]

    MD5 keys are read with RCU protection, and tcp_md5_do_add()
    might update in-place a prior key.

    Normally, typical RCU updates would allocate a new piece
    of memory. In this case only key->key and key->keylen might
    be updated, and we do not care if an incoming packet could
    see the old key, the new one, or some intermediate value,
    since changing the key on a live flow is known to be problematic
    anyway.

    We only want to make sure that in the case key->keylen
    is changed, cpus in tcp_md5_hash_key() wont try to use
    uninitialized data, or crash because key->keylen was
    read twice to feed sg_init_one() and ahash_request_set_crypt()

    Fixes: 9ea88a153001 ("tcp: md5: check md5 signature without socket lock")
    Signed-off-by: Eric Dumazet <edumazet@google.com>
    Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    net/ipv4/tcp.c | 5 ++++-
    net/ipv4/tcp_ipv4.c | 3 +++
    2 files changed, 7 insertions(+), 1 deletion(-)

    --- a/net/ipv4/tcp.c
    +++ b/net/ipv4/tcp.c
    @@ -3088,9 +3088,12 @@ EXPORT_SYMBOL(tcp_md5_hash_skb_data);

    int tcp_md5_hash_key(struct tcp_md5sig_pool *hp, const struct tcp_md5sig_key *key)
    {
    + u8 keylen = key->keylen;
    struct scatterlist sg;

    - sg_init_one(&sg, key->key, key->keylen);
    + smp_rmb(); /* paired with smp_wmb() in tcp_md5_do_add() */
    +
    + sg_init_one(&sg, key->key, keylen);
    return crypto_hash_update(&hp->md5_desc, &sg, key->keylen);
    }
    EXPORT_SYMBOL(tcp_md5_hash_key);
    --- a/net/ipv4/tcp_ipv4.c
    +++ b/net/ipv4/tcp_ipv4.c
    @@ -933,6 +933,9 @@ int tcp_md5_do_add(struct sock *sk, cons
    if (key) {
    /* Pre-existing entry - just update that one. */
    memcpy(key->key, newkey, newkeylen);
    +
    + smp_wmb(); /* pairs with smp_rmb() in tcp_md5_hash_key() */
    +
    key->keylen = newkeylen;
    return 0;
    }

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