Re: Out of tree module using LSM

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Alan Cox <[email protected]> writes:

> If I want I can have 16 threads executing code in a shared object being
> written to by ten other programs at once and shared over a network while
> we are at it. Its probably not a good idea but I can do it if I have
> reason to.

Actually the kernel prevents writing to files which are executed currently
and you can also not execute what is currently open for writing.
That is what VM_DENYWRITE is good for.

Does not work for shared libraries though -- you cannot set VM_DENYWRITE
in user mmap aka Man page says

              This flag is ignored.  (Long ago, it signalled that attempts to write to the underlying file should fail
              with ETXTBUSY.  But this was a source of denial-of-service attacks.)

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