[BUG] mwifiex: possible null-pointer dereference in mwifiex_dnld_cmd_to_fw()

[Li Tuo <islituo@gmail.com>]

Hello,

Our static analysis tool finds a possible null-pointer dereference in 
the mwifiex driver in Linux 5.14.0-rc3:

The variable cmd_node->cmd_skb->data is assigned to the variable 
host_cmd, and host_cmd is checked in:
190:    if (host_cmd == NULL || host_cmd->size == 0)

This indicates that host_cmd can be NULL.
If so, the function mwifiex_recycle_cmd_node() will be called with the 
argument cmd_node:
196:    mwifiex_recycle_cmd_node(adapter, cmd_node);

In this called function, the variable cmd_node->cmd_skb->data is 
assigned to the variable host_cmd, too.
Thus the variable host_cmd in the function mwifiex_recycle_cmd_node() 
can be also NULL.
However, it is dereferenced when calling le16_to_cpu():
144:    le16_to_cpu(host_cmd->command)

I am not quite sure whether this possible null-pointer dereference is 
real and how to fix it if it is real.
Any feedback would be appreciated, thanks!

Reported-by: TOTE Robot <oslab@tsinghua.edu.cn>

Best wishes,
Tuo Li