misc: fastrpc: Don't remove map on creater_process and device_release

Do not remove the map from the list on error path in
fastrpc_init_create_process, instead call fastrpc_map_put, to avoid
use-after-free. Do not remove it on fastrpc_device_release either,
call fastrpc_map_put instead.

The fastrpc_free_map is the only proper place to remove the map.
This is called only after the reference count is 0.

Fixes: b49f6d83 ("misc: fastrpc: Fix a possible double free")
Cc: stable <stable@kernel.org>
Co-developed-by: Ola Jeppsson <ola@snap.com>
Signed-off-by: Ola Jeppsson <ola@snap.com>
Signed-off-by: Abel Vesa <abel.vesa@linaro.org>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20221124174941.418450-3-srinivas.kandagatla@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/misc/fastrpc.c

@@ -334,6 +334,13 @@ static void fastrpc_free_map(struct kref *ref)
 		dma_buf_put(map->buf);
 	}
 
+	if (map->fl) {
+		spin_lock(&map->fl->lock);
+		list_del(&map->node);
+		spin_unlock(&map->fl->lock);
+		map->fl = NULL;
+	}
+
 	kfree(map);
 }
 
@@ -1434,12 +1441,7 @@ static int fastrpc_init_create_process(struct fastrpc_user *fl,
 	fl->init_mem = NULL;
 	fastrpc_buf_free(imem);
 err_alloc:
-	if (map) {
-		spin_lock(&fl->lock);
-		list_del(&map->node);
-		spin_unlock(&fl->lock);
 	fastrpc_map_put(map);
-	}
 err:
 	kfree(args);
 
@@ -1515,10 +1517,8 @@ static int fastrpc_device_release(struct inode *inode, struct file *file)
 		fastrpc_context_put(ctx);
 	}
 
-	list_for_each_entry_safe(map, m, &fl->maps, node) {
-		list_del(&map->node);
+	list_for_each_entry_safe(map, m, &fl->maps, node)
 		fastrpc_map_put(map);
-	}
 
 	list_for_each_entry_safe(buf, b, &fl->mmaps, node) {
 		list_del(&buf->node);