This moves the ambient capability support behind an `ambient` build tag
so that it is only compiled upon request.
Signed-off-by: Michael Crosby <crosbymichael@gmail.com>
Since Linux 4.3 ambient capabilities are available. If set these allow unprivileged child
processes to inherit capabilities, while at present there is no means to set capabilities
on non root processes, other than via filesystem capabilities which are not usually
supported in image formats.
With ambient capabilities non root processes can be given capabilities as well, and so
the main reason to use root in containers goes away, and capabilities work as expected.
The code falls back to the existing behaviour if ambient capabilities are not supported.
Signed-off-by: Justin Cormack <justin.cormack@docker.com>
Michael Crosby
Justin Cormack
Mrunal Patel