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Date: Tue, 18 Aug 2015 18:05:01 -0700
From: Chuck Lever <chuck.lever@...cle.com>
To: musl@...ts.openwall.com
Subject: Re: nfs-utils broken with musl: "select: Bad file descriptor"
>> i think this call goes wrong:
>>
>>
> http://git.linux-nfs.org/?p=steved/nfs-utils.git;a=blob;f=utils/statd/rmtcall.c;hb=HEAD#l56
>
>>
>> it loops for 100 iterations and if all ports are used
>> according to getservbyport then it FD_SET(sockfd, &SVC_FDSET);
>> with some random high sockfd (eg. 105) that is closed.
>>
>> ...so should getservbyport fail there?
>>
>> (according to strace it tries ports 883 to 982)
>
> I think the application's expectation is that it fail rather than
> returning a decimal-string-only service entity. However it looks like
> the code is written to handle the case where all 100 iterations fail
> to get an anonymous port. The problem seems to be that, when the loop
> stops due to hitting the iteration count rather than exiting with
> break, i has already been incremented past the last tmp_socket slot,
> so the close loop closes the fd that they actually want to use, later
> causing EBADF. This is purely an application bug, but it happens not
> to get noticed if getservbyport fails anywhere along the way, which
> they expect to happen in the usual case.
statd_get_socket() is hunting for a privileged source port that
is not just unused at the moment, but that is also not going to be
used by some other well-known service. This is a long-lived socket
that statd uses to communicate with the kernel. It must use a
privileged port.
if getservbyport(3) is returning something for every port that
is tried, then statd_get_socket() will fail to find a usable
port.
If it's returning 105, that suggests it has run out of retries.
It should return -1 in this case. That is a logic bug.
But is it true that every port returned by bindresvport(3) is
actually defined in /etc/services? Surely there is one open
port that can be used. What port does bindresvport(3) start
with?
--
Chuck Lever
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