On 2013/4/4 10:14, Eric W. Biederman wrote: > > 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@xxxxxxxxxx> > Reported-by: Ding Tianhong <dingtianhong@xxxxxxxxxx> > Signed-off-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx> > --- > net/unix/af_unix.c | 2 +- > 1 files changed, 1 insertions(+), 1 deletions(-) > > diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c > index f153a8d..2db702d 100644 > --- a/net/unix/af_unix.c > +++ b/net/unix/af_unix.c > @@ -1993,7 +1993,7 @@ 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; > As your opinion, I think the way is better: if (test_bit(SOCK_PASSCRED, &sock->flags)) { if (check_creds) { /* Never glue messages from different writers */ if ((UNIXCB(skb).pid != siocb->scm->pid) || (UNIXCB(skb).cred != siocb->scm->cred)) break; } else { /* Copy credentials */ scm_set_cred(siocb->scm, UNIXCB(skb).pid, UNIXCB(skb).cred); check_creds = 1; } } Ding -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html