[PATCH v2] misc: fastrpc: Fix a Use after-free-bug by race condition

[Sangsup Lee <k1rh4.lee@gmail.com>]

From: Sangsup lee <k1rh4.lee@gmail.com>

This patch adds mutex_lock for fixing an Use-after-free bug.
fastrpc_req_munmap_impl can be called concurrently in multi-threded environments.
The buf which is allocated by list_for_each_safe can be used after another thread frees it.

Signed-off-by: Sangsup lee <k1rh4.lee@gmail.com>
---
 V1 -> V2: moving the locking to ioctl.

 drivers/misc/fastrpc.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
index 93ebd174d848..aa1cf0e9f4ed 100644
--- a/drivers/misc/fastrpc.c
+++ b/drivers/misc/fastrpc.c
@@ -1901,7 +1901,9 @@ static long fastrpc_device_ioctl(struct file *file, unsigned int cmd,
 		err = fastrpc_req_mmap(fl, argp);
 		break;
 	case FASTRPC_IOCTL_MUNMAP:
+		mutex_lock(&fl->mutex);
 		err = fastrpc_req_munmap(fl, argp);
+		mutex_unlock(&fl->mutex);
 		break;
 	case FASTRPC_IOCTL_MEM_MAP:
 		err = fastrpc_req_mem_map(fl, argp);
-- 
2.25.1