When dealing with permissions, my "motto" per se is:
Use as strict a set of permissions as you can to perform your desired function.
So, I personally wouldn't set a 777 on just about anything on my system. Instead, in the case of kernel compiling in /usr/src I'd instead create me a "compile" or "kernel" group:
And then add my user to this group:
usermod -G kernel masterc
And then chown the directory to that group:
chown -R root.kernel /usr/src
And finally, ensure the chmod matched that for proper execution:
chmod 750 /usr/src
And then from that point on, whatever users I wanted to allow to compile a kernel I'd simply have to add them to the kernel group.
It may seem extensive and some may consider it a bit of overkill, especially for something in /usr/src however it's what I would consider the "proper" way as permissions are certainly something linux excels in that other OS don't.