Bug#849923: openssh-server: no login possible after upgrade on x32

[Colin Watson <cjwatson@debian.org>]

On Mon, Jan 02, 2017 at 11:36:55AM +0100, Thorsten Glaser wrote:
> After upgrading from 1:7.3p1-5 to 1:7.4p1-3 I can no longer
> 'ssh localhost' on x32; switching to openssh-server:i386 with
> the exact same configuration works, though.

sshd's seccomp sandbox is denying a clock_gettime call.  But it's more
interesting than that: its seccomp filter allows clock_gettime; but the
actual syscall being used is not the x32 clock_gettime (with bit 30
set), but the x86-64 variant instead.

You can see a similar effect like this in an x32 environment:

  strace dmesg -e

... and buried in the output you'll find something like:

  strace: syscall_228(...) in unsupported 64-bit mode of process PID=19943

Neither sshd nor dmesg is using anything like manual syscall(2) here,
just the glibc wrappers.

This feels like a glibc bug to me.  Shouldn't it be using x32 syscalls
consistently?  The x86-64 variants work, but that's not very
seccomp-friendly.  (And if necessary I can hack around it in sshd, but
if you agree that it's a glibc bug then I think it should simply be
fixed there.)

Thanks,

-- 
Colin Watson                                       [cjwatson@debian.org]