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

[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>
---
 drivers/misc/fastrpc.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
index 5310606113fe..c4b5fa4a50a6 100644
--- a/drivers/misc/fastrpc.c
+++ b/drivers/misc/fastrpc.c
@@ -1806,10 +1806,12 @@ static int fastrpc_req_munmap(struct fastrpc_user *fl, char __user *argp)
 	struct fastrpc_buf *buf = NULL, *iter, *b;
 	struct fastrpc_req_munmap req;
 	struct device *dev = fl->sctx->dev;
+	int err;
 
 	if (copy_from_user(&req, argp, sizeof(req)))
 		return -EFAULT;
 
+	mutex_lock(&fl->mutex);
 	spin_lock(&fl->lock);
 	list_for_each_entry_safe(iter, b, &fl->mmaps, node) {
 		if ((iter->raddr == req.vaddrout) && (iter->size == req.size)) {
@@ -1822,10 +1824,13 @@ static int fastrpc_req_munmap(struct fastrpc_user *fl, char __user *argp)
 	if (!buf) {
 		dev_err(dev, "mmap\t\tpt 0x%09llx [len 0x%08llx] not in list\n",
 			req.vaddrout, req.size);
+		mutex_unlock(&fl->mutex);
 		return -EINVAL;
 	}
 
-	return fastrpc_req_munmap_impl(fl, buf);
+	err = fastrpc_req_munmap_impl(fl, buf);
+	mutex_unlock(&fl->mutex);
+	return err;
 }
 
 static int fastrpc_req_mmap(struct fastrpc_user *fl, char __user *argp)
-- 
2.25.1