[Bug 217062] ZFS exec=off property does not work for mmap

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=217062

            Bug ID: 217062
           Summary: ZFS exec=off property does not work for mmap
           Product: Base System
           Version: 11.0-STABLE
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Many People
          Priority: ---
         Component: kern
          Assignee: freebsd-bugs at FreeBSD.org
          Reporter: shamaz.mazum at gmail.com

Created attachment 179941
  --> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=179941&action=edit
Test for the bug

Hello. I've noticed that you can execute a code from ZFS filesystem with exec
property set to off with mmap'ing it with PROT_READ | PROT_EXEC protection. If
this is not done at mmap time, further calls to mprotect trying to set
PROT_EXEC protection will fail.

For example, I cannot launch SBCL with core image in my no-exec home directory
(because it calls mprotect), but I can execute any code from shared libraries
in home directory if I open it with dlopen().

It seems to me as a bug, so I report.

I attach a working example to illustrate a problem. It will require some
tuning. In the attached archive compile lib.c as a shared library. Then place
it in no-exec ZFS filesystem. Then compile test-working.c and test-bug.c,
replacing hard-coded values in calls to open() and mmap() (filename and address
of return_value. You can get the address with objdump -T). Place binaries
somewhere you can execute them. Execute test-working at first. It will fail to
work if library is in no-exec FS. Then execute test-bug. It will return the
value 4 from the library no matter where it is stored. Even if it is on no-exec
FS, it will be executed.

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