Re: [patch] remove MNT_NOEXEC check for PROT_EXEC MAP_PRIVATE mmaps

[Stas Sergeev <stsp@aknet.ru>]

Hello.

Hugh Dickins wrote:
> since executables are typically mapped MAP_PRIVATE, I suspect
> your patch will simply break mmap's intended MNT_NOEXEC check.
The one with ld.so you mean? But its a user-space issue,
I haven't seen anyone claiming the opposite (and you even
explicitly confirmed it is).

> I think you need to face up to the fact that "noexec"
> doesn't suit your mount, and just leave it at that.
But noone have answered this question:
Which configuration is more secure - the one where all
the user-writable fs are mounted with "noexec" (in old
sense of noexec), or the one without "noexec" at all
because I should no longer use it here and there (actually,
everywhere)?

> But I do concede that I'm reluctant to present that patch Alan
> encouraged, adding a matching MNT_NOEXEC check to mprotect: it
> would be consistent, and I do like consistency, but in this case
> fear that change in behaviour may cause new userspace breakage.
I can't think of a single real-life example where it will
break something over whatever is broken already by the mmap
check. But I am not encouraging such a change of course.