Bug#916919: coturn 4.5.0.7-1: FTBFS, alignment problem

[Steve McIntyre]

Source: coturn
Version: 4.5.0.7-1
Severity: important
User: debian-arm at lists.debian.org
Usertags: alignment

Hi!

I've been doing a full rebuild of the Debian archive, building all
source packages targeting armel and armhf using arm64 hardware. We are
planning in future to move all of our 32-bit armel/armhf builds to
using arm64 machines, so this rebuild is to identify packages that
might have problems with this configuration.

A feature of the arm64 kernel is that it does *not* support fixing up
code with broken alignment, so code that might have built and run OK
on our older armel/armhf build machines due to kernel fixups will now
fail.

When building your package, I've found a bus error (aka alignment
fault). The full log is online at

  https://www.einval.com/debian/arm/rebuild-logs/armel/FAIL/coturn_4.5.0.7-1_armel.log

for reference

I've done a quick bit of debugging to find the source of the
bug. Here's a gdb stacktrace and variable printout to demonstrate the
problem.

(sid-armel)steve at mjolnir:~/build/coturn-4.5.0.8$ gdb bin/turnutils_rfc5769check core
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Reading symbols from bin/turnutils_rfc5769check...done.

warning: core file may not match specified executable file.
[New LWP 2415]
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/arm-linux-gnueabi/libthread_db.so.1".
Core was generated by `bin/turnutils_rfc5769check'.
Program terminated with signal SIGBUS, Bus error.
#0  decode_oauth_token_gcm (server_name=0xf797d968 <__stack_chk_guard> "", etoken=0xffa9ac60, key=<optimized out>, 
    dtoken=0xffa9a550) at src/client/ns_turn_msg.c:2611
2611                    dtoken->enc_block.timestamp = nswap64(*((uint64_t*)(decoded_field+len)));
(gdb) bt
#0  decode_oauth_token_gcm (server_name=0xf797d968 <__stack_chk_guard> "", etoken=0xffa9ac60, key=<optimized out>, 
    dtoken=0xffa9a550) at src/client/ns_turn_msg.c:2611
#1  0x00a7ca74 in check_oauth () at src/apps/rfc5769/rfc5769check.c:157
#2  main (argc=<optimized out>, argv=<optimized out>) at src/apps/rfc5769/rfc5769check.c:568
(gdb) p dtoken
$1 = (oauth_token *) 0xffa9a550
(gdb) p decoded_field
$2 = "\000\024ZksjpweoixXmvn67534m\000\000T\031\353m\000\000\000\000\016\020\064m\000\000T\031\353m\000\000\000\000\016\020", '\000' <repeats 975 times>
(gdb) p len
$3 = 22

Simply casting things like nswap64(*((uint64_t*)(decoded_field+len)))
is not safe unless you know it's guaranteed to be aligned. In this
case, it's not.

-- System Information:
Debian Release: 9.6
  APT prefers stable-updates
  APT policy: (500, 'stable-updates'), (500, 'stable-debug'), (500, 'stable')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 4.9.0-8-amd64 (SMP w/4 CPU cores)
Locale: LANG=en_GB.UTF-8, LC_CTYPE=en_GB.UTF-8 (charmap=UTF-8), LANGUAGE=en_GB.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)