[PATCH] do_swap_page() can map random data if swap read fails

There is a bug in do_swap_page(): when swap page happens to be unreadable,
page filled with random data is mapped into user address space.  The fix is
to check for PageUptodate and send SIGBUS in case of error.
Signed-Off-By: Kirill Korotaev <dev@sw.ru>
Signed-Off-By: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
Acked-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

mm/memory.c

@@ -1701,12 +1701,13 @@ static int do_swap_page(struct mm_struct * mm,
 	spin_lock(&mm->page_table_lock);
 	page_table = pte_offset_map(pmd, address);
 	if (unlikely(!pte_same(*page_table, orig_pte))) {
-		pte_unmap(page_table);
-		spin_unlock(&mm->page_table_lock);
-		unlock_page(page);
-		page_cache_release(page);
 		ret = VM_FAULT_MINOR;
-		goto out;
+		goto out_nomap;
+	}
+
+	if (unlikely(!PageUptodate(page))) {
+		ret = VM_FAULT_SIGBUS;
+		goto out_nomap;
 	}
 
 	/* The page isn't present yet, go ahead with the fault. */
@@ -1741,6 +1742,12 @@ static int do_swap_page(struct mm_struct * mm,
 	spin_unlock(&mm->page_table_lock);
 out:
 	return ret;
+out_nomap:
+	pte_unmap(page_table);
+	spin_unlock(&mm->page_table_lock);
+	unlock_page(page);
+	page_cache_release(page);
+	goto out;
 }
 
 /*