[arp] Increase robustness of ARP discarder

Take ownership from the ARP cache at the start of arp_destroy(), to
ensure that no code path can lead to arp_destroy() being re-entered.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

diff --git a/src/net/arp.c b/src/net/arp.c
index d96cb4ccce97d5ffd1d546ac541fae02790f5c27..b94eb9064b25b7965f84d158ddc418d3935dad1f 100644 (file)
--- a/src/net/arp.c
+++ b/src/net/arp.c
@@ -180,13 +180,16 @@ static void arp_destroy ( struct arp_entry *arp, int rc ) {
        struct net_device *netdev = arp->netdev;
        struct net_protocol *net_protocol = arp->net_protocol;
        struct io_buffer *iobuf;
-       struct io_buffer *tmp;
+
+       /* Take ownership from cache */
+       list_del ( &arp->list );
 
        /* Stop timer */
        stop_timer ( &arp->timer );
 
        /* Discard any outstanding I/O buffers */
-       list_for_each_entry_safe ( iobuf, tmp, &arp->tx_queue, list ) {
+       while ( ( iobuf = list_first_entry ( &arp->tx_queue, struct io_buffer,
+                                            list ) ) != NULL ) {
                DBGC2 ( arp, "ARP %p %s %s %s discarding deferred packet: "
                        "%s\n", arp, netdev->name, net_protocol->name,
                        net_protocol->ntoa ( arp->net_dest ), strerror ( rc ) );
@@ -198,8 +201,7 @@ static void arp_destroy ( struct arp_entry *arp, int rc ) {
               net_protocol->name, net_protocol->ntoa ( arp->net_dest ),
               strerror ( rc ) );
 
-       /* Remove from cache and drop reference */
-       list_del ( &arp->list );
+       /* Drop remaining reference */
        ref_put ( &arp->refcnt );
 }
 
@@ -518,12 +520,13 @@ static unsigned int arp_discard ( void ) {
        struct arp_entry *arp;
 
        /* Drop oldest cache entry, if any */
-       list_for_each_entry_reverse ( arp, &arp_entries, list ) {
+       arp = list_last_entry ( &arp_entries, struct arp_entry, list );
+       if ( arp ) {
                arp_destroy ( arp, -ENOBUFS );
                return 1;
+       } else {
+               return 0;
        }
-
-       return 0;
 }
 
 /** ARP cache discarder