dingtianhong <dingtianhong@xxxxxxxxxx> writes: > 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; > } > } It is a smidge clearer in intent, but there is no functional difference. The lines get really long. Shrug. Patches are always welcome. Beyond getting something correct for the right reasons I don't care. Eric -- 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