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    Subject[PATCH 5.12 041/110] net/packet: annotate data race in packet_sendmsg()
    Date
    From: Eric Dumazet <edumazet@google.com>

    [ Upstream commit d1b5bee4c8be01585033be9b3a8878789285285f ]

    There is a known race in packet_sendmsg(), addressed
    in commit 32d3182cd2cd ("net/packet: fix race in tpacket_snd()")

    Now we have data_race(), we can use it to avoid a future KCSAN warning,
    as syzbot loves stressing af_packet sockets :)

    Signed-off-by: Eric Dumazet <edumazet@google.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    net/packet/af_packet.c | 9 ++++++---
    1 file changed, 6 insertions(+), 3 deletions(-)

    diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
    index c52557ec7fb3..84d8921391c3 100644
    --- a/net/packet/af_packet.c
    +++ b/net/packet/af_packet.c
    @@ -3034,10 +3034,13 @@ static int packet_sendmsg(struct socket *sock, struct msghdr *msg, size_t len)
    struct sock *sk = sock->sk;
    struct packet_sock *po = pkt_sk(sk);

    - if (po->tx_ring.pg_vec)
    + /* Reading tx_ring.pg_vec without holding pg_vec_lock is racy.
    + * tpacket_snd() will redo the check safely.
    + */
    + if (data_race(po->tx_ring.pg_vec))
    return tpacket_snd(po, msg);
    - else
    - return packet_snd(sock, msg, len);
    +
    + return packet_snd(sock, msg, len);
    }

    /*
    --
    2.30.2
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