Merge branch 'eth-fix-bugs-in-ntuple-filter-reporting'

Jakub Kicinski says:

====================
eth: fix bugs in ntuple filter reporting

Looking thru some reports prompted by:
  Add new way to add BPF LSM hooks
  https://lore.kernel.org/20260831110934.241898-1-a.s.protopopov@gmail.com

I/Claude noticed 3 drivers with buggy n-tuple filter dump.
Fix these drivers, add a hopefully clearer mention in the doc.
====================

Link: https://patch.msgid.link/20260903032611.3000029-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/dsa/bcm_sf2_cfp.c

@@ -1088,6 +1088,8 @@ static int bcm_sf2_cfp_rule_get_all(struct bcm_sf2_priv *priv,
 	unsigned int index = 1, rules_cnt = 0;
 
 	for_each_set_bit_from(index, priv->cfp.unique, priv->num_cfp_rules) {
+		if (rules_cnt == nfc->rule_cnt)
+			return -EMSGSIZE;
 		rule_locs[rules_cnt] = index;
 		rules_cnt++;
 	}

drivers/net/dsa/mv88e6xxx/chip.c

@@ -2438,6 +2438,7 @@ static int mv88e6xxx_get_rxnfc(struct dsa_switch *ds, int port,
 	struct ethtool_rx_flow_spec *fs = &rxnfc->fs;
 	struct mv88e6xxx_chip *chip = ds->priv;
 	struct mv88e6xxx_policy *policy;
+	u32 cnt = 0;
 	int err;
 	int id;
 
@@ -2463,11 +2464,18 @@ static int mv88e6xxx_get_rxnfc(struct dsa_switch *ds, int port,
 		break;
 	case ETHTOOL_GRXCLSRLALL:
 		rxnfc->data = 0;
-		rxnfc->rule_cnt = 0;
-		idr_for_each_entry(&chip->policies, policy, id)
-			if (policy->port == port)
-				rule_locs[rxnfc->rule_cnt++] = id;
 		err = 0;
+		idr_for_each_entry(&chip->policies, policy, id) {
+			if (policy->port != port)
+				continue;
+			if (cnt == rxnfc->rule_cnt) {
+				err = -EMSGSIZE;
+				break;
+			}
+			rule_locs[cnt++] = id;
+		}
+		if (!err)
+			rxnfc->rule_cnt = cnt;
 		break;
 	default:
 		err = -EOPNOTSUPP;

drivers/net/ethernet/netronome/nfp/nfp_net_ethtool.c

@@ -1421,7 +1421,8 @@ static int nfp_net_get_fs_rule(struct nfp_net *nn, struct ethtool_rxnfc *cmd)
 	return -ENOENT;
 }
 
-static int nfp_net_get_fs_loc(struct nfp_net *nn, u32 *rule_locs)
+static int nfp_net_get_fs_loc(struct nfp_net *nn, struct ethtool_rxnfc *cmd,
+			      u32 *rule_locs)
 {
 	struct nfp_fs_entry *entry;
 	u32 count = 0;
@@ -1429,8 +1430,12 @@ static int nfp_net_get_fs_loc(struct nfp_net *nn, u32 *rule_locs)
 	if (!(nn->cap_w1 & NFP_NET_CFG_CTRL_FLOW_STEER))
 		return -EOPNOTSUPP;
 
-	list_for_each_entry(entry, &nn->fs.list, node)
+	list_for_each_entry(entry, &nn->fs.list, node) {
+		if (count == cmd->rule_cnt)
+			return -EMSGSIZE;
 		rule_locs[count++] = entry->loc;
+	}
+	cmd->rule_cnt = count;
 
 	return 0;
 }
@@ -1455,7 +1460,7 @@ static int nfp_net_get_rxnfc(struct net_device *netdev,
 		return nfp_net_get_fs_rule(nn, cmd);
 	case ETHTOOL_GRXCLSRLALL:
 		cmd->data = NFP_FS_MAX_ENTRY;
-		return nfp_net_get_fs_loc(nn, rule_locs);
+		return nfp_net_get_fs_loc(nn, cmd, rule_locs);
 	default:
 		return -EOPNOTSUPP;
 	}
@@ -1698,8 +1703,14 @@ static int nfp_net_fs_add(struct nfp_net *nn, struct ethtool_rxnfc *cmd)
 
 			nn->fs.count--;
 			err = nfp_net_fs_add_hw(nn, new);
-			if (err)
+			if (err) {
+				/* mbox broken, adding the old rule back will
+				 * likely also fail.
+				 */
+				list_del(&entry->node);
+				kfree(entry);
 				goto err;
+			}
 
 			nn->fs.count++;
 			list_replace(&entry->node, &new->node);

include/linux/ethtool.h

@@ -1057,6 +1057,12 @@ struct kernel_ethtool_ts_info {
  * @get_sset_count: Get number of strings that @get_strings will write.
  * @get_rxnfc: Get RX flow classification rules.  Returns a negative
  *	error code or zero.
+ *	Note that for %ETHTOOL_GRXCLSRLALL rule_cnt and size of the arrays
+ *	is user-provided, and not guaranteed to match what driver would
+ *	have reported via %ETHTOOL_GRXCLSRLCNT. Drivers must return -%EMSGSIZE
+ *	when rule_cnt is too small. rule_locs is %NULL when rule_cnt is zero.
+ *	On success drivers must set rule_cnt to the number of locations they
+ *	filled in, the core copies out exactly that many.
  * @set_rxnfc: Set RX flow classification rules.  Returns a negative
  *	error code or zero.
  * @flash_device: Write a firmware image to device's flash memory.