wifi: iwlwifi: mvm: handle debugfs names more carefully

With debugfs=off, we can get here with the dbgfs_dir being
an ERR_PTR(). Instead of checking for all this, which is
often flagged as a mistake, simply handle the names here
more carefully by printing them, then we don't need extra
checks.

Also, while checking, I noticed theoretically 'buf' is too
small, so fix that size as well.

Cc: stable@vger.kernel.org
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=218422
Fixes: c36235ac ("wifi: iwlwifi: mvm: rework debugfs handling")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://msgid.link/20240320232419.4dc1eb3dd015.I32f308b0356ef5bcf8d188dd98ce9b210e3ab9fd@changeidSigned-off-by: Johannes Berg <johannes.berg@intel.com>

drivers/net/wireless/intel/iwlwifi/mvm/debugfs-vif.c

@@ -748,7 +748,9 @@ void iwl_mvm_vif_dbgfs_add_link(struct iwl_mvm *mvm, struct ieee80211_vif *vif)
 {
 	struct dentry *dbgfs_dir = vif->debugfs_dir;
 	struct iwl_mvm_vif *mvmvif = iwl_mvm_vif_from_mac80211(vif);
-	char buf[100];
+	char buf[3 * 3 + 11 + (NL80211_WIPHY_NAME_MAXLEN + 1) +
+		 (7 + IFNAMSIZ + 1) + 6 + 1];
+	char name[7 + IFNAMSIZ + 1];
 
 	/* this will happen in monitor mode */
 	if (!dbgfs_dir)
@@ -761,10 +763,11 @@ void iwl_mvm_vif_dbgfs_add_link(struct iwl_mvm *mvm, struct ieee80211_vif *vif)
 	 * find
 	 * netdev:wlan0 -> ../../../ieee80211/phy0/netdev:wlan0/iwlmvm/
 	 */
-	snprintf(buf, 100, "../../../%pd3/iwlmvm", dbgfs_dir);
+	snprintf(name, sizeof(name), "%pd", dbgfs_dir);
+	snprintf(buf, sizeof(buf), "../../../%pd3/iwlmvm", dbgfs_dir);
 
-	mvmvif->dbgfs_slink = debugfs_create_symlink(dbgfs_dir->d_name.name,
-						     mvm->debugfs_dir, buf);
+	mvmvif->dbgfs_slink =
+		debugfs_create_symlink(name, mvm->debugfs_dir, buf);
 }
 
 void iwl_mvm_vif_dbgfs_rm_link(struct iwl_mvm *mvm, struct ieee80211_vif *vif)