net: mscc: ocelot: mark traps with a bool instead of keeping them in a list

Since the blamed commit, VCAP filters can appear on more than one list.
If their action is "trap", they are chained on ocelot->traps via
filter->trap_list. This is in addition to their normal placement on the
VCAP block->rules list head.

Therefore, when we free a VCAP filter, we must remove it from all lists
it is a member of, including ocelot->traps.

There are at least 2 bugs which are direct consequences of this design
decision.

First is the incorrect usage of list_empty(), meant to denote whether
"filter" is chained into ocelot->traps via filter->trap_list.
This does not do the correct thing, because list_empty() checks whether
"head->next == head", but in our case, head->next == head->prev == NULL.
So we dereference NULL pointers and die when we call list_del().

Second is the fact that not all places that should remove the filter
from ocelot->traps do so. One example is ocelot_vcap_block_remove_filter(),
which is where we have the main kfree(filter). By keeping freed filters
in ocelot->traps we end up in a use-after-free in
felix_update_trapping_destinations().

Attempting to fix all the buggy patterns is a whack-a-mole game which
makes the driver unmaintainable. Actually this is what the previous
patch version attempted to do:
https://patchwork.kernel.org/project/netdevbpf/patch/20220503115728.834457-3-vladimir.oltean@nxp.com/

but it introduced another set of bugs, because there are other places in
which create VCAP filters, not just ocelot_vcap_filter_create():

- ocelot_trap_add()
- felix_tag_8021q_vlan_add_rx()
- felix_tag_8021q_vlan_add_tx()

Relying on the convention that all those code paths must call
INIT_LIST_HEAD(&filter->trap_list) is not going to scale.

So let's do what should have been done in the first place and keep a
bool in struct ocelot_vcap_filter which denotes whether we are looking
at a trapping rule or not. Iterating now happens over the main VCAP IS2
block->rules. The advantage is that we no longer risk having stale
references to a freed filter, since it is only present in that list.

Fixes: e42bd4ed09aa ("net: mscc: ocelot: keep traps in a list")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

2 files changed, 4 insertions, 11 deletions

diff --git a/drivers/net/ethernet/mscc/ocelot.c b/drivers/net/ethernet/mscc/ocelot.c
index ca71b62a44dc..20ceac81a2c2 100644
--- a/drivers/net/ethernet/mscc/ocelot.c
+++ b/drivers/net/ethernet/mscc/ocelot.c
@@ -1622,7 +1622,7 @@ int ocelot_trap_add(struct ocelot *ocelot, int port,
 		trap->action.mask_mode = OCELOT_MASK_MODE_PERMIT_DENY;
 		trap->action.port_mask = 0;
 		trap->take_ts = take_ts;
-		list_add_tail(&trap->trap_list, &ocelot->traps);
+		trap->is_trap = true;
 		new = true;
 	}
 
@@ -1634,10 +1634,8 @@ int ocelot_trap_add(struct ocelot *ocelot, int port,
 		err = ocelot_vcap_filter_replace(ocelot, trap);
 	if (err) {
 		trap->ingress_port_mask &= ~BIT(port);
-		if (!trap->ingress_port_mask) {
-			list_del(&trap->trap_list);
+		if (!trap->ingress_port_mask)
 			kfree(trap);
-		}
 		return err;
 	}
 
@@ -1657,11 +1655,8 @@ int ocelot_trap_del(struct ocelot *ocelot, int port, unsigned long cookie)
 		return 0;
 
 	trap->ingress_port_mask &= ~BIT(port);
-	if (!trap->ingress_port_mask) {
-		list_del(&trap->trap_list);
-
+	if (!trap->ingress_port_mask)
 		return ocelot_vcap_filter_del(ocelot, trap);
-	}
 
 	return ocelot_vcap_filter_replace(ocelot, trap);
 }
diff --git a/drivers/net/ethernet/mscc/ocelot_flower.c b/drivers/net/ethernet/mscc/ocelot_flower.c
index 03b5e59d033e..a9b26b3002be 100644
--- a/drivers/net/ethernet/mscc/ocelot_flower.c
+++ b/drivers/net/ethernet/mscc/ocelot_flower.c
@@ -295,7 +295,7 @@ static int ocelot_flower_parse_action(struct ocelot *ocelot, int port,
 			filter->action.cpu_copy_ena = true;
 			filter->action.cpu_qu_num = 0;
 			filter->type = OCELOT_VCAP_FILTER_OFFLOAD;
-			list_add_tail(&filter->trap_list, &ocelot->traps);
+			filter->is_trap = true;
 			break;
 		case FLOW_ACTION_POLICE:
 			if (filter->block_id == PSFP_BLOCK_ID) {
@@ -878,8 +878,6 @@ int ocelot_cls_flower_replace(struct ocelot *ocelot, int port,
 
 	ret = ocelot_flower_parse(ocelot, port, ingress, f, filter);
 	if (ret) {
-		if (!list_empty(&filter->trap_list))
-			list_del(&filter->trap_list);
 		kfree(filter);
 		return ret;
 	}