FILE__EXECMOD and other assorted file permission layout issues

[Eric Paris <eparis@redhat.com>]

I started poking around the other day and realized FILE__EXECMOD and how
it is used can be problematic.  Namely with blk files it is possible to
cause the kernel to check SECCLASS_BLK_FILE + FILE__EXECMOD.  Turns out
0x00080000 isn't defined for SECCLASS_BLK_FILE.  It appears at some
point in history the same thing was found for char files and we added
EXECUTE_NO_TRANS and ENTRYPOINT to get it to line up.

We can't leave it the way it is for block files as if a perm ever gets
to there the kernel could check the wrong thing.  The 'easiest' fix is
to move the EXECMOD declaration into COMMON_FILE_PERMS, and I'm assuming
you can't call mmap + write + mprotect on a socket, else we need to move
it to COMMON_FILE_SOCK_PERMS if I understand correctly.

If you agree it's a problem we should address and this is a good method
I'll look into the details.

The other thing I noticed is that we don't use FILE__SWAPON at all.
Should I just drop SWAPON from the list of kernel perms?

OPEN.  I did the horrid per secclass open perms.  Should I move that
into COMMON_FILE_SOCK_PERMS and drop all of the special case code?

-Eric


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