OS X 10.11 buffer overflow with deep filesystem hierarchy

Even with just namelen+1 you can still get undefined behavior. This is because if namelen is shorter than the padding of the object struct FTSENT, the beginning of the next object struct stat, will overlap with the previous object.

The correct solution is to make sure that the next object begins after the first one, and still remains inside of the allocated block. This is a good example, why the struct hack just isn't worth it, and it itself is arguably undefined behavior.

To allocate it all, remove the struct hack and simply call the malloc three times, once for each struct and then for the string. If one allocation is required, then allocate enough memory for all three objects separated by enough alignment padding. Doing this will allocate a couple of bytes more which is a couple percent overall, but at least your code will be correct. Since they don't pack the struct thus loosing bytes for internal padding anyway, I can't understand why the usage of the struct hack.