Re: openssh and sendmsg() problem

[orc <orc@sibserver.ru>]

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)
> > > > > 
> > > > 
> > > > src/network/sendmsg.c has an ifdef for long>int case
> > > > 
> > > > i don't know what it's supposed to do
> > > 
> > > It's there because the kernel expects certain fields to be long
> > > but POSIX requires them to be int. Thus the syscall wrapper has
> > > to copy the userspace struct (with int and padding) to a
> > > kernel-format struct (with the padding filled with 0's so it's a
> > > valid long).
> > 
> > And how to deal with this? Should it be openssh workaround or fix in
> > musl itself?
> 
> There's nothing to be dealt with here; musl already works around the
> kernel bug. Something is wrong, possibly in this code or elsewhere,
> but I don't know what and I don't see anything obviously wrong with
> the syscall. Can you compare the strace to what happens on glibc?
> 
> Rich

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