[PATCH] mmap PROT_NONE fix for NX patch

This works around the current PROT_NONE problem from elf binaries that
do not have the PT_GNU_STACK so that the do not have execute permission.

The problem was that setting "def_flags" to include the VM_EXEC bit for
compatibility reasons would also make PROT_NONE pages executable, which
is obviously not correct.
Signed-off-by: Daniel McNeil <daniel@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

mm/mmap.c

@@ -792,6 +792,12 @@ unsigned long do_mmap_pgoff(struct file * file, unsigned long addr,
 	vm_flags = calc_vm_prot_bits(prot) | calc_vm_flag_bits(flags) |
 			mm->def_flags | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC;
 
+	/*
+	 * mm->def_flags might have VM_EXEC set, which PROT_NONE does NOT want.
+	 */
+	if (prot == PROT_NONE)
+		vm_flags &= ~VM_EXEC;
+
 	if (flags & MAP_LOCKED) {
 		if (!capable(CAP_IPC_LOCK))
 			return -EPERM;