[PATCH 2/3] mm/usercopy: Detect vmalloc overruns

["Matthew Wilcox (Oracle)" <willy@infradead.org>]

If you have a vmalloc() allocation, or an address from calling vmap(),
you cannot overrun the vm_area which describes it, regardless of the
size of the underlying allocation.  This probably doesn't do much for
security because vmalloc comes with guard pages these days, but it
prevents usercopy aborts when copying to a vmap() of smaller pages.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 mm/usercopy.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/mm/usercopy.c b/mm/usercopy.c
index ac95b22fbbce..7bfc4f9ed1e4 100644
--- a/mm/usercopy.c
+++ b/mm/usercopy.c
@@ -17,6 +17,7 @@
 #include <linux/sched/task.h>
 #include <linux/sched/task_stack.h>
 #include <linux/thread_info.h>
+#include <linux/vmalloc.h>
 #include <linux/atomic.h>
 #include <linux/jump_label.h>
 #include <asm/sections.h>
@@ -236,6 +237,14 @@ static inline void check_heap_object(const void *ptr, unsigned long n,
 		return;
 	}
 
+	if (is_vmalloc_addr(ptr)) {
+		struct vm_struct *vm = find_vm_area(ptr);
+
+		if (ptr + n > vm->addr + vm->size)
+			usercopy_abort("vmalloc", NULL, to_user, 0, n);
+		return;
+	}
+
 	page = virt_to_head_page(ptr);
 
 	if (PageSlab(page)) {
-- 
2.32.0