selinux: implement mmap on /selinux/policy

/selinux/policy allows a user to copy the policy back out of the kernel.
This patch allows userspace to actually mmap that file and use it directly.

Signed-off-by: Eric Paris <eparis@redhat.com>
Signed-off-by: James Morris <jmorris@namei.org>

1 files changed, 44 insertions, 0 deletions

diff --git a/security/selinux/selinuxfs.c b/security/selinux/selinuxfs.c
index 8eb102c72606..87e0556bae70 100644
--- a/security/selinux/selinuxfs.c
+++ b/security/selinux/selinuxfs.c
@@ -439,9 +439,53 @@ out:
         return ret;
 }
 
+static int sel_mmap_policy_fault(struct vm_area_struct *vma,
+                                 struct vm_fault *vmf)
+{
+        struct policy_load_memory *plm = vma->vm_file->private_data;
+        unsigned long offset;
+        struct page *page;
+
+        if (vmf->flags & (FAULT_FLAG_MKWRITE | FAULT_FLAG_WRITE))
+                return VM_FAULT_SIGBUS;
+
+        offset = vmf->pgoff << PAGE_SHIFT;
+        if (offset >= roundup(plm->len, PAGE_SIZE))
+                return VM_FAULT_SIGBUS;
+
+        page = vmalloc_to_page(plm->data + offset);
+        get_page(page);
+
+        vmf->page = page;
+
+        return 0;
+}
+
+static struct vm_operations_struct sel_mmap_policy_ops = {
+        .fault = sel_mmap_policy_fault,
+        .page_mkwrite = sel_mmap_policy_fault,
+};
+
+int sel_mmap_policy(struct file *filp, struct vm_area_struct *vma)
+{
+        if (vma->vm_flags & VM_SHARED) {
+                /* do not allow mprotect to make mapping writable */
+                vma->vm_flags &= ~VM_MAYWRITE;
+
+                if (vma->vm_flags & VM_WRITE)
+                        return -EACCES;
+        }
+
+        vma->vm_flags |= VM_RESERVED;
+        vma->vm_ops = &sel_mmap_policy_ops;
+
+        return 0;
+}
+
 static const struct file_operations sel_policy_ops = {
         .open           = sel_open_policy,
         .read           = sel_read_policy,
+        .mmap           = sel_mmap_policy,
         .release        = sel_release_policy,
 };