[PATCH] nl80211: Avoid bogus ENFILE with use_existing

[Yanghan Ye]

When use_existing is set, nl80211_create_iface() may be called for an
interface that already exists. The current code still sends
NL80211_CMD_NEW_INTERFACE first and only falls back to reusing the
existing netdev after the create attempt fails.

This can produce a misleading ENFILE/"Too many open files in system"
failure in the log even though the subsequent use_existing path succeeds.

Check for an existing interface before attempting to create it when
use_existing is allowed. Keep the fallback path for races where the
interface appears after the initial check or for other create failures
that leave an existing netdev behind.

Signed-off-by: Yanghan Ye <yyh94306 at gmail.com>
---
 src/drivers/driver_nl80211.c | 36 +++++++++++++++++++++++-------------
 1 file changed, 23 insertions(+), 13 deletions(-)

diff --git a/src/drivers/driver_nl80211.c b/src/drivers/driver_nl80211.c
index 469a542..ff66efa 100644
--- a/src/drivers/driver_nl80211.c
+++ b/src/drivers/driver_nl80211.c
@@ -6925,6 +6925,24 @@ static int nl80211_create_iface_once(struct wpa_driver_nl80211_data *drv,
 }
 
 
+static int nl80211_use_existing_iface(struct wpa_driver_nl80211_data *drv,
+				      const char *ifname,
+				      enum nl80211_iftype iftype,
+				      const u8 *addr)
+{
+	wpa_printf(MSG_DEBUG, "nl80211: Continue using existing interface %s",
+		   ifname);
+	if (addr && iftype != NL80211_IFTYPE_MONITOR &&
+	    linux_set_ifhwaddr(drv->global->ioctl_sock, ifname, addr) < 0 &&
+	    (linux_set_iface_flags(drv->global->ioctl_sock, ifname, 0) < 0 ||
+	     linux_set_ifhwaddr(drv->global->ioctl_sock, ifname, addr) < 0 ||
+	     linux_set_iface_flags(drv->global->ioctl_sock, ifname, 1) < 0))
+		return -1;
+
+	return -ENFILE;
+}
+
+
 int nl80211_create_iface(struct wpa_driver_nl80211_data *drv,
 			 const char *ifname, enum nl80211_iftype iftype,
 			 const u8 *addr, int wds,
@@ -6933,25 +6951,17 @@ int nl80211_create_iface(struct wpa_driver_nl80211_data *drv,
 {
 	int ret;
 
+	if (use_existing && if_nametoindex(ifname))
+		return nl80211_use_existing_iface(drv, ifname, iftype, addr);
+
 	ret = nl80211_create_iface_once(drv, ifname, iftype, addr, wds, handler,
 					arg);
 
 	/* if error occurred and interface exists already */
 	if (ret < 0 && if_nametoindex(ifname)) {
 		if (use_existing) {
-			wpa_printf(MSG_DEBUG, "nl80211: Continue using existing interface %s",
-				   ifname);
-			if (addr && iftype != NL80211_IFTYPE_MONITOR &&
-			    linux_set_ifhwaddr(drv->global->ioctl_sock, ifname,
-					       addr) < 0 &&
-			    (linux_set_iface_flags(drv->global->ioctl_sock,
-						   ifname, 0) < 0 ||
-			     linux_set_ifhwaddr(drv->global->ioctl_sock, ifname,
-						addr) < 0 ||
-			     linux_set_iface_flags(drv->global->ioctl_sock,
-						   ifname, 1) < 0))
-					return -1;
-			return -ENFILE;
+			return nl80211_use_existing_iface(drv, ifname, iftype,
+							  addr);
 		}
 		wpa_printf(MSG_INFO, "Try to remove and re-create %s", ifname);
 
-- 
2.43.0