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From: Rich Felker <dalias@aerifal.cx>
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Subject: Re: openssh and sendmsg() problem
Date: Tue, 26 Jun 2012 15:08:23 -0400
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On Wed, Jun 27, 2012 at 02:16:40AM +0800, orc wrote:
> On Tue, 26 Jun 2012 13:32:05 -0400
> Rich Felker <dalias@aerifal.cx> wrote:
> 
> > On Wed, Jun 27, 2012 at 01:24:41AM +0800, orc wrote:
> > > On Tue, 26 Jun 2012 12:01:06 -0400
> > > Rich Felker <dalias@aerifal.cx> wrote:
> > > 
> > > > On Tue, Jun 26, 2012 at 02:00:17PM +0200, Szabolcs Nagy wrote:
> > > > > * orc <orc@sibserver.ru> [2012-06-26 19:01:46 +0800]:
> > > > > > strace shows that sendmsg system call returns EINVAL:
> > > > > > 
> > > > > > sendmsg(5, {msg_name(0)=NULL, msg_iov(1)=[{"\0", 1}],
> > > > > > msg_controllen=24, {cmsg_len=20, cmsg_level=SOL_SOCKET, cmsg_
> > > > > > type=SCM_RIGHTS, {4, 385875968}}, msg_flags=0}, 0) = -1 EINVAL
> > > > > > (Invalid argument)
> > > > > > 
> 
> strace from glibc system on this syscall:
> 
> sendmsg(5, {msg_name(0)=NULL, msg_iov(1)=[{"\0", 1}], msg_controllen=24, {cmsg_len=20, cmsg_level=SOL_SOCKET, cmsg_type=SCM_RIGHTS, {4}}, msg_flags=0}, 0) = 1
> sendmsg(5, {msg_name(0)=NULL, msg_iov(1)=[{"\0", 1}], msg_controllen=24, {cmsg_len=20, cmsg_level=SOL_SOCKET, cmsg_type=SCM_RIGHTS, {6}}, msg_flags=0}, 0) = 1

I don't quite understand this from the strace, but it looks like
there's an issue with the size of cmsg structures on 64-bit machines
due to another buggy kernel socklen_t/size_t mismatch. I'm not sure
how it can be worked around, but musl's failure to work around it is a
flaw that needs to be fixed. glibc just violates POSIX and defines
the wrong type.

Rich