[PATCH net v2] ice: Fix use-after-scope in ice_sched_add_nodes_to_layer()

[NeKon69 <nobodqwe@gmail.com>]

Commit 7fb09a737536 ("ice: Modify recursive way of adding nodes")
changed ice_sched_add_nodes_to_layer() from recursive control flow to an
iterative loop.

Inside the loop, first_teid_ptr may be set to the address of a
block-local variable:

    u32 temp;
    ...
    if (num_added)
        first_teid_ptr = &temp;

On the next loop iteration, first_teid_ptr may be passed to
ice_sched_add_nodes_to_hw_layer(), after temp from the previous
iteration has gone out of scope.

Instead of keeping temporary storage for later calls, allow
first_node_teid to be NULL when the caller does not need the TEID.

This was found by Clang with LifetimeSafety enabled while testing C
language support on a Linux allmodconfig build.

Fixes: 7fb09a737536 ("ice: Modify recursive way of adding nodes")
Link: https://github.com/llvm/llvm-project/pull/203270
Signed-off-by: NeKon69 <nobodqwe@gmail.com>
---
v2:
- Allow first_node_teid to be NULL when callers do not need the TEID.
- Pass NULL after the first TEID has already been returned instead of using
  temporary stack storage.
- Update kernel-doc for helpers accepting NULL.
- Link to v1: https://lore.kernel.org/netdev/20260613101440.80190-1-nobodqwe@gmail.com/
- Compile-tested with:
  make drivers/net/ethernet/intel/ice/ice_sched.o

 drivers/net/ethernet/intel/ice/ice_sched.c | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/drivers/net/ethernet/intel/ice/ice_sched.c b/drivers/net/ethernet/intel/ice/ice_sched.c
index fff0c1afdb41..89e191c839b1 100644
--- a/drivers/net/ethernet/intel/ice/ice_sched.c
+++ b/drivers/net/ethernet/intel/ice/ice_sched.c
@@ -895,7 +895,8 @@ void ice_sched_cleanup_all(struct ice_hw *hw)
  * @layer: layer number to add nodes
  * @num_nodes: number of nodes
  * @num_nodes_added: pointer to num nodes added
- * @first_node_teid: if new nodes are added then return the TEID of first node
+ * @first_node_teid: if new nodes are added then return the TEID of first node,
+ *                   may be NULL
  * @prealloc_nodes: preallocated nodes struct for software DB
  *
  * This function add nodes to HW as well as to SW DB for a given layer
@@ -1000,7 +1001,7 @@ ice_sched_add_elems(struct ice_port_info *pi, struct ice_sched_node *tc_node,
 		if (!pi->sib_head[tc_node->tc_num][layer])
 			pi->sib_head[tc_node->tc_num][layer] = new_node;
 
-		if (i == 0)
+		if (first_node_teid && i == 0)
 			*first_node_teid = teid;
 	}
 
@@ -1015,7 +1016,7 @@ ice_sched_add_elems(struct ice_port_info *pi, struct ice_sched_node *tc_node,
  * @parent: pointer to parent node
  * @layer: layer number to add nodes
  * @num_nodes: number of nodes to be added
- * @first_node_teid: pointer to the first node TEID
+ * @first_node_teid: pointer to the first node TEID, may be NULL
  * @num_nodes_added: pointer to number of nodes added
  *
  * Add nodes into specific HW layer.
@@ -1078,7 +1079,6 @@ ice_sched_add_nodes_to_layer(struct ice_port_info *pi,
 	*num_nodes_added = 0;
 	while (*num_nodes_added < num_nodes) {
 		u16 max_child_nodes, num_added = 0;
-		u32 temp;
 
 		status = ice_sched_add_nodes_to_hw_layer(pi, tc_node, parent,
 							 layer,	new_num_nodes,
@@ -1109,13 +1109,11 @@ ice_sched_add_nodes_to_layer(struct ice_port_info *pi,
 			 * try the next available sibling.
 			 */
 			parent = ice_sched_find_next_vsi_node(parent);
-			/* Don't modify the first node TEID memory if the
-			 * first node was added already in the above call.
-			 * Instead send some temp memory for all other
-			 * recursive calls.
+			/* Don't modify the first node TEID memory if the first node
+			 * was added already in the above call.
 			 */
 			if (num_added)
-				first_teid_ptr = &temp;
+				first_teid_ptr = NULL;
 
 			new_num_nodes = num_nodes - *num_nodes_added;
 		}
-- 
2.54.0