qlcnic: prevent ->dcb use-after-free on qlcnic_dcb_enable() failure

adapter->dcb would get silently freed inside qlcnic_dcb_enable() in
case qlcnic_dcb_attach() would return an error, which always happens
under OOM conditions. This would lead to use-after-free because both
of the existing callers invoke qlcnic_dcb_get_info() on the obtained
pointer, which is potentially freed at that point.

Propagate errors from qlcnic_dcb_enable(), and instead free the dcb
pointer at callsite using qlcnic_dcb_free(). This also removes the now
unused qlcnic_clear_dcb_ops() helper, which was a simple wrapper around
kfree() also causing memory leaks for partially initialized dcb.

Found by Linux Verification Center (linuxtesting.org) with the SVACE
static analysis tool.

Fixes: 3c44bba1 ("qlcnic: Disable DCB operations from SR-IOV VFs")
Reviewed-by: Michal Swiatkowski <michal.swiatkowski@linux.intel.com>
Signed-off-by: Daniil Tatianin <d-tatianin@yandex-team.ru>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/qlogic/qlcnic/qlcnic_83xx_init.c

@@ -2505,7 +2505,13 @@ int qlcnic_83xx_init(struct qlcnic_adapter *adapter)
 		goto disable_mbx_intr;
 
 	qlcnic_83xx_clear_function_resources(adapter);
-	qlcnic_dcb_enable(adapter->dcb);
+
+	err = qlcnic_dcb_enable(adapter->dcb);
+	if (err) {
+		qlcnic_dcb_free(adapter->dcb);
+		goto disable_mbx_intr;
+	}
+
 	qlcnic_83xx_initialize_nic(adapter, 1);
 	qlcnic_dcb_get_info(adapter->dcb);
 

drivers/net/ethernet/qlogic/qlcnic/qlcnic_dcb.h

@@ -41,11 +41,6 @@ struct qlcnic_dcb {
 	unsigned long			state;
 };
 
-static inline void qlcnic_clear_dcb_ops(struct qlcnic_dcb *dcb)
-{
-	kfree(dcb);
-}
-
 static inline int qlcnic_dcb_get_hw_capability(struct qlcnic_dcb *dcb)
 {
 	if (dcb && dcb->ops->get_hw_capability)
@@ -112,9 +107,8 @@ static inline void qlcnic_dcb_init_dcbnl_ops(struct qlcnic_dcb *dcb)
 		dcb->ops->init_dcbnl_ops(dcb);
 }
 
-static inline void qlcnic_dcb_enable(struct qlcnic_dcb *dcb)
+static inline int qlcnic_dcb_enable(struct qlcnic_dcb *dcb)
 {
-	if (dcb && qlcnic_dcb_attach(dcb))
-		qlcnic_clear_dcb_ops(dcb);
+	return dcb ? qlcnic_dcb_attach(dcb) : 0;
 }
 #endif

drivers/net/ethernet/qlogic/qlcnic/qlcnic_main.c

@@ -2599,7 +2599,13 @@ qlcnic_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
 			 "Device does not support MSI interrupts\n");
 
 	if (qlcnic_82xx_check(adapter)) {
-		qlcnic_dcb_enable(adapter->dcb);
+		err = qlcnic_dcb_enable(adapter->dcb);
+		if (err) {
+			qlcnic_dcb_free(adapter->dcb);
+			dev_err(&pdev->dev, "Failed to enable DCB\n");
+			goto err_out_free_hw;
+		}
+
 		qlcnic_dcb_get_info(adapter->dcb);
 		err = qlcnic_setup_intr(adapter);