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    Subject[PATCH 5.19 0569/1157] dccp: put dccp_qpolicy_full() and dccp_qpolicy_push() in the same lock
    Date
    From: Hangyu Hua <hbh25y@gmail.com>

    [ Upstream commit a41b17ff9dacd22f5f118ee53d82da0f3e52d5e3 ]

    In the case of sk->dccps_qpolicy == DCCPQ_POLICY_PRIO, dccp_qpolicy_full
    will drop a skb when qpolicy is full. And the lock in dccp_sendmsg is
    released before sock_alloc_send_skb and then relocked after
    sock_alloc_send_skb. The following conditions may lead dccp_qpolicy_push
    to add skb to an already full sk_write_queue:

    thread1--->lock
    thread1--->dccp_qpolicy_full: queue is full. drop a skb
    thread1--->unlock
    thread2--->lock
    thread2--->dccp_qpolicy_full: queue is not full. no need to drop.
    thread2--->unlock
    thread1--->lock
    thread1--->dccp_qpolicy_push: add a skb. queue is full.
    thread1--->unlock
    thread2--->lock
    thread2--->dccp_qpolicy_push: add a skb!
    thread2--->unlock

    Fix this by moving dccp_qpolicy_full.

    Fixes: b1308dc015eb ("[DCCP]: Set TX Queue Length Bounds via Sysctl")
    Signed-off-by: Hangyu Hua <hbh25y@gmail.com>
    Link: https://lore.kernel.org/r/20220729110027.40569-1-hbh25y@gmail.com
    Signed-off-by: Jakub Kicinski <kuba@kernel.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    net/dccp/proto.c | 10 +++++-----
    1 file changed, 5 insertions(+), 5 deletions(-)

    diff --git a/net/dccp/proto.c b/net/dccp/proto.c
    index eb8e128e43e8..e13641c65f88 100644
    --- a/net/dccp/proto.c
    +++ b/net/dccp/proto.c
    @@ -736,11 +736,6 @@ int dccp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)

    lock_sock(sk);

    - if (dccp_qpolicy_full(sk)) {
    - rc = -EAGAIN;
    - goto out_release;
    - }
    -
    timeo = sock_sndtimeo(sk, noblock);

    /*
    @@ -759,6 +754,11 @@ int dccp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
    if (skb == NULL)
    goto out_release;

    + if (dccp_qpolicy_full(sk)) {
    + rc = -EAGAIN;
    + goto out_discard;
    + }
    +
    if (sk->sk_state == DCCP_CLOSED) {
    rc = -ENOTCONN;
    goto out_discard;
    --
    2.35.1


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