Thanks for looking at this!
I tested your change in Xenial (couldn't install the tools package since i assume you built it against Artful's libraries, but it didn't matter) and it does appear to restore the previous behaviour:
% lsb_release -ds Ubuntu 16.04.3 LTS % uname -r 4.13.0-19-generic
% ls -Ali /bin/true /ro/bin/true 131819 -rwxr-xr-x 1 root root 27280 Mar 2 2017 /bin/true 131819 -rwxr-xr-x 1 root root 27280 Mar 2 2017 /ro/bin/true % /bin/true --version | head -1 true (GNU coreutils) 8.25
% sudo cp /bin/true /tmp/ % sudo mv /tmp/true /ro/bin/
% ls -Ali /bin/true /ro/bin/true 131819 -rwxr-xr-x 0 root root 27280 Mar 2 2017 /bin/true 131110 -rwxr-xr-x 1 root root 27280 Dec 8 11:57 /ro/bin/true % /bin/true --version | head -1 true (GNU coreutils) 8.25
(On the 'stock' kernel the last command would produce an error.)
I don't see any error messages in the kernel log either.
Thanks for looking at this!
I tested your change in Xenial (couldn't install the tools package since i assume you built it against Artful's libraries, but it didn't matter) and it does appear to restore the previous behaviour:
% lsb_release -ds
Ubuntu 16.04.3 LTS
% uname -r
4.13.0-19-generic
% ls -Ali /bin/true /ro/bin/true
131819 -rwxr-xr-x 1 root root 27280 Mar 2 2017 /bin/true
131819 -rwxr-xr-x 1 root root 27280 Mar 2 2017 /ro/bin/true
% /bin/true --version | head -1
true (GNU coreutils) 8.25
% sudo cp /bin/true /tmp/
% sudo mv /tmp/true /ro/bin/
% ls -Ali /bin/true /ro/bin/true
131819 -rwxr-xr-x 0 root root 27280 Mar 2 2017 /bin/true
131110 -rwxr-xr-x 1 root root 27280 Dec 8 11:57 /ro/bin/true
% /bin/true --version | head -1
true (GNU coreutils) 8.25
(On the 'stock' kernel the last command would produce an error.)
I don't see any error messages in the kernel log either.