Which is also why trying to do anything productive on a smartphone is such an uphill battle. Arbitrary programs not being able to exchange arbitrary files is totally crippling for any use-cases that go off the rails of what one single app wants to let you do.
for src in $(find . -type '*.png')
do
sdir="$(echo "${src}" | dirname)"
name="$(echo "${src}" | basename)"
dstdir="/mnt/www/images/${sdir}"
optipng -out "${dstdir}/${name}" "${src}"
convert -scale 120x120\> "${src}" "${dstdir}/small_${name}"
done
You could do literally the same and you didn't even need to drop to the console.
Opening any random file should be reserved to just a few core applications.
The problem is more that I do not believe any distro is shipping a default-deny policy. Unknown programs are simply given the kitchen sink rather than having, say, user friendly prompts saying "this program has no access control and wants to open X or use Y, allow?"
But we definitely have the technology, and it does not take any heavy overhead isolation to do it.
Arch has a grsec kernel in the repos if you want one...
There are two ways to do MAC - applications (or the distro) provides the profiles, that restrict execution to just what the program will use, and if it ever asks for anything else it should be suspect for exploitation. The other one is where you put your programs in learning mode, and that only hardens you against future exploits, not current ones, and you also lose the protection against untrusted software because by default everything is untrusted and you must trust everything on a case by case basis.
Say, VLC team had argued that a video player may need to open a supplementary subtitle file. If application can be only granted access to a single video file - that's impossible. I think there were other examples, but I don't remember those off-hand.