[Devel] [PATCH rh7 v2 2/2] kasan: fix kmemleak false-positive in kasan_module_alloc()

[Andrey Ryabinin]

Kmemleak reports the following leak:
	unreferenced object 0xfffffbfff41ea000 (size 20480):
	comm "modprobe", pid 65199, jiffies 4298875551 (age 542.568s)
	hex dump (first 32 bytes):
	  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
	  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
	backtrace:
	  [<ffffffff82354f5e>] kmemleak_alloc+0x4e/0xc0
	  [<ffffffff8152e718>] __vmalloc_node_range+0x4b8/0x740
	  [<ffffffff81574072>] kasan_module_alloc+0x72/0xc0
	  [<ffffffff810efe68>] module_alloc+0x78/0xb0
	  [<ffffffff812f6a24>] module_alloc_update_bounds+0x14/0x70
	  [<ffffffff812f8184>] layout_and_allocate+0x16f4/0x3c90
	  [<ffffffff812faa1f>] load_module+0x2ff/0x6690
	  [<ffffffff813010b6>] SyS_finit_module+0x136/0x170
	  [<ffffffff8239bbc9>] system_call_fastpath+0x16/0x1b
	  [<ffffffffffffffff>] 0xffffffffffffffff

kasan_module_alloc() allocates shadow memory for module and frees it on module
unloading. But it doesn't store the pointer to allocated shadow memory because
it could be calculated from the shadowed address, i.e. kasan_mem_to_shadow(addr).
Since kmemleak cannot find pointer to allocated shadow, it thinks that memory leaked.
Use kmemleak_ignore() to tell kmemleak that this is not a leak and this memory
doesn't contain any pointers.

https://jira.sw.ru/browse/PSBM-41328

Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
---
Changes since v1:
 - Use kmemleak_ignore() instead of kmemleak_not_leak(), since shadow memory doesn't contain
   any pointers

 mm/kasan/kasan.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c
index d6798bc..a00c6a7 100644
--- a/mm/kasan/kasan.c
+++ b/mm/kasan/kasan.c
@@ -19,6 +19,7 @@
 #include <linux/export.h>
 #include <linux/init.h>
 #include <linux/kernel.h>
+#include <linux/kmemleak.h>
 #include <linux/memblock.h>
 #include <linux/memory.h>
 #include <linux/mm.h>
@@ -425,6 +426,7 @@ int kasan_module_alloc(void *addr, size_t size)
 
 	if (ret) {
 		find_vm_area(addr)->flags |= VM_KASAN;
+		kmemleak_ignore(ret);
 		return 0;
 	}
 
-- 
2.4.10