[PATCH] net/ncsi: prevent a couple array underflows

[Dan Carpenter]

We recently refactored this code and introduced a static checker
warning.  Smatch complains that if cmd->index is zero then we would
underflow the arrays.  That's obviously true.

The question is whether we prevent cmd->index from being zero at a
different level.  I've looked at the code and I don't immediately see
a check for that.

Fixes: 062b3e1b6d4f ("net/ncsi: Refactor MAC, VLAN filters")
Signed-off-by: Dan Carpenter <dan.carpen...@oracle.com>

diff --git a/net/ncsi/ncsi-rsp.c b/net/ncsi/ncsi-rsp.c
index ce9497966ebe..a6b7c7d5c829 100644
--- a/net/ncsi/ncsi-rsp.c
+++ b/net/ncsi/ncsi-rsp.c
@@ -347,7 +347,7 @@ static int ncsi_rsp_handler_svf(struct ncsi_request *nr)
 
        cmd = (struct ncsi_cmd_svf_pkt *)skb_network_header(nr->cmd);
        ncf = &nc->vlan_filter;
-       if (cmd->index > ncf->n_vids)
+       if (cmd->index == 0 || cmd->index > ncf->n_vids)
                return -ERANGE;
 
        /* Add or remove the VLAN filter. Remember HW indexes from 1 */
@@ -445,7 +445,8 @@ static int ncsi_rsp_handler_sma(struct ncsi_request *nr)
        ncf = &nc->mac_filter;
        bitmap = &ncf->bitmap;
 
-       if (cmd->index > ncf->n_uc + ncf->n_mc + ncf->n_mixed)
+       if (cmd->index == 0 ||
+           cmd->index > ncf->n_uc + ncf->n_mc + ncf->n_mixed)
                return -ERANGE;
 
        index = (cmd->index - 1) * ETH_ALEN;