Date: Fri, 18 Jan 2008 14:54:36 -0700 (MST) From: "M. Warner Losh" <imp@bsdimp.com> To: jhay@meraka.org.za Cc: freebsd-arm@FreeBSD.ORG, des@FreeBSD.ORG Subject: Re: sshd broken on arm? Message-ID: <20080118.145436.-1540399028.imp@bsdimp.com> In-Reply-To: <20080118191638.GA30155@zibbi.meraka.csir.co.za> References: <20080118185634.GA28843@zibbi.meraka.csir.co.za> <20080118.120152.-345488389.imp@bsdimp.com> <20080118191638.GA30155@zibbi.meraka.csir.co.za>
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In message: <20080118191638.GA30155@zibbi.meraka.csir.co.za>
John Hay <jhay@meraka.org.za> writes:
: On Fri, Jan 18, 2008 at 12:01:52PM -0700, M. Warner Losh wrote:
: > In message: <20080118185634.GA28843@zibbi.meraka.csir.co.za>
: > John Hay <jhay@meraka.org.za> writes:
: > : On Fri, Jan 18, 2008 at 10:17:47AM -0700, M. Warner Losh wrote:
: > : > In message: <4790D750.4060702@errno.com>
: > : > Sam Leffler <sam@errno.com> writes:
: > : > : John Hay wrote:
: > : > : > On Thu, Jan 17, 2008 at 12:58:54PM +0200, John Hay wrote:
: > : > : >
: > : > : >> Hi Guys,
: > : > : >>
: > : > : >> I just did a new build using RELENG_7 for the arm (Avila boards) and then
: > : > : >> found that I cannot ssh into them. The sshd crash with a bus error just
: > : > : >> after you entered your username and password. My build of mid November
: > : > : >> did not do it. Anybody got ideas?
: > : > : >>
: > : > : >> The last part of "sshd -Dddd" on the arm board looks like this:
: > : > : >>
: > : > : >> debug1: server_input_channel_req: channel 0 request pty-req reply 0
: > : > : >> debug1: session_by_channel: session 0 channel 0
: > : > : >> debug1: session_input_channel_req: session 0 req pty-req
: > : > : >> debug1: Allocating pty.
: > : > : >> debug3: mm_request_send entering: type 25
: > : > : >> debug3: monitor_read: checking request 25
: > : > : >> debug3: mm_answer_pty entering
: > : > : >> debug1: session_new: init
: > : > : >> debug1: session_new: session 0
: > : > : >> debug3: mm_pty_allocate: waiting for MONITOR_ANS_PTY
: > : > : >> debug3: mm_request_receive_expect entering: type 26
: > : > : >> debug3: mm_request_receive entering
: > : > : >> debug3: mm_request_send entering: type 26
: > : > : >> ssh_mm_receive_fd: recvmsg: expected received 1 got 0
: > : > : >> debug1: do_cleanup
: > : > : >> debug1: PAM: cleanup
: > : > : >> Bus error (core dumped)
: > : > : >> debug3: PAM: sshpam_thread_cleanup entering
: > : > : >>
: > : > : >
: > : > : > Ok, I found the problem. It looks like something changed and now the
: > : > : > alignment for the char tmp[...] array in monitor_fdpass.c:mm_send_fd
: > : > : > and monitor_fdpass.c:mm_receive_fd is different and the arm processors
: > : > : > do not like it. Attached is my quick fix.
: > : > : >
: > : > : > One question that I have is if we should just fix all of these "problems"
: > : > : > or should something be changed so that these things are aligned again? In
: > : > : > the last month or two I have come across quite a few of these things that
: > : > : > used to work on the arm and now do not anymore because of alignment
: > : > : > changes.
: > : > : >
: > : > : > (I have cc'ed des@ because his name pitch up a lot in the openssh cvs logs.
: > : > : > :-)
: > : > : >
: > : > :
: > : > : This used to work fine so the problem is elsewhere. Sounds like a
: > : > : toolchain or header change is the root cause.
: > : >
: > : > Or some subtle change in the kernel that isn't using the macro (or is
: > : > now and didn't used to be).
: > :
: > : Hmmm Just to make sure that I'm on the right page. On FreeBSD ARM one
: > : is not supposed to be able to access unaligned memory? Ie. an int that
: > : does not start on an address that is a multiple of 4.
: > :
: > : In a C function if you have something like "char tmp[4]", can you assume
: > : that the compiler will align it on a 4 byte boundary or can it do it on
: > : a byte boundary?
: > :
: > : If one cannot access unaligned ints and char arrays are not int aligned,
: > : then we were just lucky that the code worked at some stage.
: >
: > You are correct. The fact that it seemed to work meant that we were
: > either getting lucky before, or there was some critical code on the
: > kernel side that has accidentally been removed...
:
: I don't think the kernel will make a difference. The bus error happened
: on line 64 of openssh/monitor_fdpass.c. That is before the kernel was
: called (sendmsg())... Except if the kernel aligned the stack differently.
OK. Maybe the right fix is to add '__aligned(4)' to the declaration?
: > : > John, I don't suppose you'd have time for a binary search?
: > :
: > : I'll see what I can do, but it will be slow going.
: >
: > Bad sshd with kernels going back in time should be sufficient...
:
: That should go faster. :-) I'll look at it tomorrow between power failures.
: South Africa has a power shortage at the moment and they are load shedding
: us in 3-6 hour sessions. :-(((
:-(
Warner
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