net: cxgb3_main: fix potential Spectre v1

t.qset_idx can be indirectly controlled by user-space, hence leading to a potential exploitation of the Spectre variant 1 vulnerability.

This issue was detected with the help of Smatch:

drivers/net/ethernet/chelsio/cxgb3/cxgb3_main.c:2286 cxgb_extension_ioctl()
warn: potential spectre issue 'adapter->msix_info'

Fix this by sanitizing t.qset_idx before using it to index adapter->msix_info

Notice that given that speculation windows are large, the policy is to kill the speculation on the first load and not worry if it can be completed with a dependent load/store [1].

[1] https://marc.info/?l=linux-kernel&m=152449131114778&w=2

---
 drivers/net/ethernet/chelsio/cxgb3/cxgb3_main.c | 2 ++
 1 file changed, 2 insertions(+)

index 7b795ed..a19172d 100644
@@ -51,6 +51,7 @@
 #include <linux/sched.h>
 #include <linux/slab.h>
 #include <linux/uaccess.h>
+#include <linux/nospec.h>
 
 #include "common.h"
 #include "cxgb3_ioctl.h"

@@ -2268,6 +2269,7 @@ static int cxgb_extension_ioctl(struct net_device *dev, void __user *useraddr)
 
 		if (t.qset_idx >= nqsets)
 			return -EINVAL;
+		t.qset_idx = array_index_nospec(t.qset_idx, nqsets);
 
 		q = &adapter->params.sge.qset[q1 + t.qset_idx];
 		t.rspq_size = q->rspq_size;

2.7.4

From: "Gustavo A. R. Silva" <[email protected]>
Date: Mon, 16 Jul 2018 20:59:58 -0500

Applied, thanks.