[PATCH net] ice: fix invalid check for empty list in ice_sched_assoc_vsi_to_agg()

[Jakob Koschel]

The code implicitly assumes that the list iterator finds a correct
handle. If 'vsi_handle' is not found the 'old_agg_vsi_info' was
pointing to an bogus memory location. For safety a separate list
iterator variable should be used to make the != NULL check on
'old_agg_vsi_info' correct under any circumstances.

Additionally Linus proposed to avoid any use of the list iterator
variable after the loop, in the attempt to move the list iterator
variable declaration into the macro to avoid any potential misuse after
the loop. Using it in a pointer comparision after the loop is undefined
behavior and should be omitted if possible [1].

Link: https://lore.kernel.org/all/CAHk-=wgRr_D8CB-D9Kg-c=EHreAsk5SqXPwr9Y7k9sA6cWXJ6w@xxxxxxxxxxxxxx/ [1]
Signed-off-by: Jakob Koschel <jkl820.git@xxxxxxxxx>
---
 drivers/net/ethernet/intel/ice/ice_sched.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/intel/ice/ice_sched.c b/drivers/net/ethernet/intel/ice/ice_sched.c
index 4eca8d195ef0..b7682de0ae05 100644
--- a/drivers/net/ethernet/intel/ice/ice_sched.c
+++ b/drivers/net/ethernet/intel/ice/ice_sched.c
@@ -2788,7 +2788,7 @@ static int
 ice_sched_assoc_vsi_to_agg(struct ice_port_info *pi, u32 agg_id,
 			   u16 vsi_handle, unsigned long *tc_bitmap)
 {
-	struct ice_sched_agg_vsi_info *agg_vsi_info, *old_agg_vsi_info = NULL;
+	struct ice_sched_agg_vsi_info *agg_vsi_info, *iter, *old_agg_vsi_info = NULL;
 	struct ice_sched_agg_info *agg_info, *old_agg_info;
 	struct ice_hw *hw = pi->hw;
 	int status = 0;
@@ -2806,11 +2806,13 @@ ice_sched_assoc_vsi_to_agg(struct ice_port_info *pi, u32 agg_id,
 	if (old_agg_info && old_agg_info != agg_info) {
 		struct ice_sched_agg_vsi_info *vtmp;
 
-		list_for_each_entry_safe(old_agg_vsi_info, vtmp,
+		list_for_each_entry_safe(iter, vtmp,
 					 &old_agg_info->agg_vsi_list,
 					 list_entry)
-			if (old_agg_vsi_info->vsi_handle == vsi_handle)
+			if (iter->vsi_handle == vsi_handle) {
+				old_agg_vsi_info = iter;
 				break;
+			}
 	}
 
 	/* check if entry already exist */

---
base-commit: eeac8ede17557680855031c6f305ece2378af326
change-id: 20230301-ice-fix-invalid-iterator-found-check-0a3e5b43dfb3

Best regards,
-- 
Jakob Koschel <jkl820.git@xxxxxxxxx>