[PATCH net-next v4] net: core: failover: enforce mandatory ops and clean up redundant checks

[Zeeshan Ahmad]

The failover framework requires 'ops' to be functional. Currently,
failover_register() allows an instance to be registered with NULL
ops, which leads to inconsistent NULL checks and potential NULL
pointer dereferences in the slave registration paths.

Harden the entry point by requiring non-NULL ops in
failover_register(). This ensures the 'fops' pointer is guaranteed
to be valid for any successfully registered failover instance.
Consequently, remove the now redundant NULL checks for 'fops'
throughout the module to simplify the logic.

Signed-off-by: Zeeshan Ahmad <zeeshanahmad022019@xxxxxxxxx>
---
v4:
 - Harden failover_register() to forbid NULL ops as suggested by
   Jakub Kicinski.
 - Remove all redundant NULL checks for fops throughout the module.
 - Remove the Fixes tag and target net-next, as this is now categorized
   as a refactor/cleanup rather than a standalone bug fix.
v3:
 - Move the fops NULL check to the top of the function before any
   dereferences occur, as suggested by Dan Carpenter.
v2:
 - Wrap the dereference in an if(fops) block instead of an early return 
   based on feedback from Simon Horman.

 net/core/failover.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/net/core/failover.c b/net/core/failover.c
index 0eb2e0ec875b..11bb183c7a1b 100644
--- a/net/core/failover.c
+++ b/net/core/failover.c
@@ -59,7 +59,7 @@ static int failover_slave_register(struct net_device *slave_dev)
 	if (!failover_dev)
 		goto done;
 
-	if (fops && fops->slave_pre_register &&
+	if (fops->slave_pre_register &&
 	    fops->slave_pre_register(slave_dev, failover_dev))
 		goto done;
 
@@ -82,7 +82,7 @@ static int failover_slave_register(struct net_device *slave_dev)
 
 	slave_dev->priv_flags |= (IFF_FAILOVER_SLAVE | IFF_NO_ADDRCONF);
 
-	if (fops && fops->slave_register &&
+	if (fops->slave_register &&
 	    !fops->slave_register(slave_dev, failover_dev))
 		return NOTIFY_OK;
 
@@ -115,7 +115,7 @@ int failover_slave_unregister(struct net_device *slave_dev)
 	if (!failover_dev)
 		goto done;
 
-	if (fops && fops->slave_pre_unregister &&
+	if (fops->slave_pre_unregister &&
 	    fops->slave_pre_unregister(slave_dev, failover_dev))
 		goto done;
 
@@ -123,7 +123,7 @@ int failover_slave_unregister(struct net_device *slave_dev)
 	netdev_upper_dev_unlink(slave_dev, failover_dev);
 	slave_dev->priv_flags &= ~(IFF_FAILOVER_SLAVE | IFF_NO_ADDRCONF);
 
-	if (fops && fops->slave_unregister &&
+	if (fops->slave_unregister &&
 	    !fops->slave_unregister(slave_dev, failover_dev))
 		return NOTIFY_OK;
 
@@ -149,7 +149,7 @@ static int failover_slave_link_change(struct net_device *slave_dev)
 	if (!netif_running(failover_dev))
 		goto done;
 
-	if (fops && fops->slave_link_change &&
+	if (fops->slave_link_change &&
 	    !fops->slave_link_change(slave_dev, failover_dev))
 		return NOTIFY_OK;
 
@@ -174,7 +174,7 @@ static int failover_slave_name_change(struct net_device *slave_dev)
 	if (!netif_running(failover_dev))
 		goto done;
 
-	if (fops && fops->slave_name_change &&
+	if (fops->slave_name_change &&
 	    !fops->slave_name_change(slave_dev, failover_dev))
 		return NOTIFY_OK;
 
@@ -244,7 +244,7 @@ struct failover *failover_register(struct net_device *dev,
 {
 	struct failover *failover;
 
-	if (dev->type != ARPHRD_ETHER)
+	if (dev->type != ARPHRD_ETHER || !ops)
 		return ERR_PTR(-EINVAL);
 
 	failover = kzalloc_obj(*failover);
-- 
2.43.0