Why replacing running executable file is forbidden, but overwriting of memory mapped shared object is allowed ?

[valdis.kletnieks at vt.edu]

On Fri, 10 Nov 2017 21:04:22 +0300, Lev Olshvang said:

> I am going to patch inode reference count of  mapped shared libs 

Congrats. You just corrupted your file system.

Hint 1:  What happens if you decrement the count by one unnecessarily,
and later on, probably during system shutdown, the reference count drops
to zero instead of one?

Hint 2:  What happens if you incremented the count, and at system shutdown,
there's still a reference left when the kernel tries to unmount and sync the
filesystem?
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