[PATCH v2] hwtracing: stm: fix vfree() nonexistent vm_area

[Kefeng Wang]

If device_add() in stm_register_device() fails, stm_device_release()
is called by put_device() to free stm, free stm again on err_device
path will trigger following warning,

  Trying to vfree() nonexistent vm area (0000000054b5e7bc)
  WARNING: CPU: 0 PID: 6004 at mm/vmalloc.c:1595 __vunmap+0x72/0x480 mm/vmalloc.c:1594
  Kernel panic - not syncing: panic_on_warn set ...
  CPU: 0 PID: 6004 Comm: syz-executor.0 Tainted: G         C 5.1.0+ #28
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1ubuntu1 04/01/2014
  Call Trace:
   __vfree+0x2a/0x80 mm/vmalloc.c:1658
   _vfree+0x49/0x70 mm/vmalloc.c:1688
   stm_register_device+0x295/0x330 [stm_core]
   dummy_stm_init+0xfe/0x1e0 [dummy_stm]
   do_one_initcall+0xb9/0x3b5 init/main.c:914
   do_init_module+0xe0/0x330 kernel/module.c:3468
   load_module+0x38eb/0x4270 kernel/module.c:3819
   __do_sys_finit_module+0x162/0x190 kernel/module.c:3909
   do_syscall_64+0x72/0x2a0 arch/x86/entry/common.c:298
   entry_SYSCALL_64_after_hwframe+0x49/0xbe

Change error handling path and only free stm once if device_add() fails
to fix it.

Reported-by: Hulk Robot <hulkci@xxxxxxxxxx>
Signed-off-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
---
 drivers/hwtracing/stm/core.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/hwtracing/stm/core.c b/drivers/hwtracing/stm/core.c
index e55b902560de..afb7999eb863 100644
--- a/drivers/hwtracing/stm/core.c
+++ b/drivers/hwtracing/stm/core.c
@@ -885,8 +885,10 @@ int stm_register_device(struct device *parent, struct stm_data *stm_data,
 		return -ENOMEM;
 
 	stm->major = register_chrdev(0, stm_data->name, &stm_fops);
-	if (stm->major < 0)
-		goto err_free;
+	if (stm->major < 0) {
+		vfree(stm);
+		return stm->major;
+	}
 
 	device_initialize(&stm->dev);
 	stm->dev.devt = MKDEV(stm->major, 0);
@@ -932,8 +934,6 @@ int stm_register_device(struct device *parent, struct stm_data *stm_data,
 
 	/* matches device_initialize() above */
 	put_device(&stm->dev);
-err_free:
-	vfree(stm);
 
 	return err;
 }
-- 
2.20.1