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    Subject[PATCH 5.6 184/194] bpf: Fix sk_psock refcnt leak when receiving message
    Date
    From: Xiyu Yang <xiyuyang19@fudan.edu.cn>

    commit 18f02ad19e2c2a1d9e1d55a4e1c0cbf51419151c upstream.

    tcp_bpf_recvmsg() invokes sk_psock_get(), which returns a reference of
    the specified sk_psock object to "psock" with increased refcnt.

    When tcp_bpf_recvmsg() returns, local variable "psock" becomes invalid,
    so the refcount should be decreased to keep refcount balanced.

    The reference counting issue happens in several exception handling paths
    of tcp_bpf_recvmsg(). When those error scenarios occur such as "flags"
    includes MSG_ERRQUEUE, the function forgets to decrease the refcnt
    increased by sk_psock_get(), causing a refcnt leak.

    Fix this issue by calling sk_psock_put() or pulling up the error queue
    read handling when those error scenarios occur.

    Fixes: e7a5f1f1cd000 ("bpf/sockmap: Read psock ingress_msg before sk_receive_queue")
    Signed-off-by: Xiyu Yang <xiyuyang19@fudan.edu.cn>
    Signed-off-by: Xin Tan <tanxin.ctf@gmail.com>
    Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
    Reviewed-by: Jakub Sitnicki <jakub@cloudflare.com>
    Link: https://lore.kernel.org/bpf/1587872115-42805-1-git-send-email-xiyuyang19@fudan.edu.cn
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    net/ipv4/tcp_bpf.c | 9 ++++++---
    1 file changed, 6 insertions(+), 3 deletions(-)

    --- a/net/ipv4/tcp_bpf.c
    +++ b/net/ipv4/tcp_bpf.c
    @@ -121,14 +121,17 @@ int tcp_bpf_recvmsg(struct sock *sk, str
    struct sk_psock *psock;
    int copied, ret;

    + if (unlikely(flags & MSG_ERRQUEUE))
    + return inet_recv_error(sk, msg, len, addr_len);
    +
    psock = sk_psock_get(sk);
    if (unlikely(!psock))
    return tcp_recvmsg(sk, msg, len, nonblock, flags, addr_len);
    - if (unlikely(flags & MSG_ERRQUEUE))
    - return inet_recv_error(sk, msg, len, addr_len);
    if (!skb_queue_empty(&sk->sk_receive_queue) &&
    - sk_psock_queue_empty(psock))
    + sk_psock_queue_empty(psock)) {
    + sk_psock_put(sk, psock);
    return tcp_recvmsg(sk, msg, len, nonblock, flags, addr_len);
    + }
    lock_sock(sk);
    msg_bytes_ready:
    copied = __tcp_bpf_recvmsg(sk, psock, msg, len, flags);

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