[PATCH] fix MADV_REMOVE vulnerability (CVE-2006-1524 for real this time)

madvise_remove needs to respect file and mmap protections.
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

mm/madvise.c

@@ -168,6 +168,9 @@ static long madvise_remove(struct vm_area_struct *vma,
 			return -EINVAL;
 	}
 
+	if ((vma->vm_flags & (VM_SHARED|VM_WRITE)) != (VM_SHARED|VM_WRITE))
+		return -EACCES;
+
 	mapping = vma->vm_file->f_mapping;
 
 	offset = (loff_t)(start - vma->vm_start)