slirp: Prevent recursion of if_start

if_start can be called recursively via if_encap. Avoid this as our
scheme of dequeuing packets is not compatible with this.

CC: Fabien Chouteau <chouteau@adacore.com>
CC: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>
CC: Stefan Weil <sw@weilnetz.de>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>

2 files changed, 11 insertions, 1 deletions

diff --git a/if.c b/if.c
index a9e68cf..ff9f572 100644
--- a/if.c
+++ b/if.c
@@ -159,10 +159,17 @@ void if_start(Slirp *slirp)
 
     DEBUG_CALL("if_start");
 
+    if (slirp->if_start_busy) {
+        return;
+    }
+    slirp->if_start_busy = true;
+
     while (slirp->if_queued) {
         /* check if we can really output */
-        if (!slirp_can_output(slirp->opaque))
+        if (!slirp_can_output(slirp->opaque)) {
+            slirp->if_start_busy = false;
             return;
+        }
 
         /*
          * See which queue to get next packet from
@@ -216,4 +223,6 @@ void if_start(Slirp *slirp)
     }
 
     slirp->if_queued = requeued;
+
+    slirp->if_start_busy = false;
 }
diff --git a/slirp.h b/slirp.h
index 27e3b8c..4c76187 100644
--- a/slirp.h
+++ b/slirp.h
@@ -239,6 +239,7 @@ struct Slirp {
     struct mbuf if_fastq; /* fast queue (for interactive data) */
     struct mbuf if_batchq; /* queue for non-interactive data */
     struct mbuf *next_m; /* pointer to next mbuf to output */
+    bool if_start_busy; /* avoid if_start recursion */
 
     /* ip states */
     struct ipq ipq; /* ip reass. queue */