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    Subject[ 24/34] af_unix: If we dont care about credentials coallesce all messages
    Date
    3.4-stable review patch.  If anyone has any objections, please let me know.

    ------------------


    From: "Eric W. Biederman" <ebiederm@xmission.com>

    [ Upstream commit 0e82e7f6dfeec1013339612f74abc2cdd29d43d2 ]

    It was reported that the following LSB test case failed
    https://lsbbugs.linuxfoundation.org/attachment.cgi?id=2144 because we
    were not coallescing unix stream messages when the application was
    expecting us to.

    The problem was that the first send was before the socket was accepted
    and thus sock->sk_socket was NULL in maybe_add_creds, and the second
    send after the socket was accepted had a non-NULL value for sk->socket
    and thus we could tell the credentials were not needed so we did not
    bother.

    The unnecessary credentials on the first message cause
    unix_stream_recvmsg to start verifying that all messages had the same
    credentials before coallescing and then the coallescing failed because
    the second message had no credentials.

    Ignoring credentials when we don't care in unix_stream_recvmsg fixes a
    long standing pessimization which would fail to coallesce messages when
    reading from a unix stream socket if the senders were different even if
    we did not care about their credentials.

    I have tested this and verified that the in the LSB test case mentioned
    above that the messages do coallesce now, while the were failing to
    coallesce without this change.

    Reported-by: Karel Srot <ksrot@redhat.com>
    Reported-by: Ding Tianhong <dingtianhong@huawei.com>
    Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    net/unix/af_unix.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- a/net/unix/af_unix.c
    +++ b/net/unix/af_unix.c
    @@ -1986,7 +1986,7 @@ again:
    if ((UNIXCB(skb).pid != siocb->scm->pid) ||
    (UNIXCB(skb).cred != siocb->scm->cred))
    break;
    - } else {
    + } else if (test_bit(SOCK_PASSCRED, &sock->flags)) {
    /* Copy credentials */
    scm_set_cred(siocb->scm, UNIXCB(skb).pid, UNIXCB(skb).cred);
    check_creds = 1;



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