From: Gerd Hoffmann <kraxel@redhat.com>
Date: Mon, 18 Apr 2016 09:11:38 +0200
Subject: [PATCH] ehci: apply limit to iTD/sidt descriptors
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Commit "156a2e4 ehci: make idt processing more robust" tries to avoid a
DoS by the guest (create a circular iTD queue and let qemu ehci
emulation run in circles forever).  Unfortunately this has two problems:
First it misses the case of siTDs, and second it reportedly breaks
FreeBSD.

So lets go for a different approach: just count the number of iTDs and
siTDs we have seen per frame and apply a limit.  That should really
catch all cases now.

Reported-by: 杜少博 <dushaobo@360.cn>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
(cherry picked from commit 1ae3f2f178087711f9591350abad133525ba93f2)
---
 hw/usb/hcd-ehci.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/hw/usb/hcd-ehci.c b/hw/usb/hcd-ehci.c
index d6d7de3..8dbfbe3 100644
--- a/hw/usb/hcd-ehci.c
+++ b/hw/usb/hcd-ehci.c
@@ -2003,6 +2003,7 @@ static int ehci_state_writeback(EHCIQueue *q)
 static void ehci_advance_state(EHCIState *ehci, int async)
 {
     EHCIQueue *q = NULL;
+    int itd_count = 0;
     int again;
 
     do {
@@ -2027,10 +2028,12 @@ static void ehci_advance_state(EHCIState *ehci, int async)
 
         case EST_FETCHITD:
             again = ehci_state_fetchitd(ehci, async);
+            itd_count++;
             break;
 
         case EST_FETCHSITD:
             again = ehci_state_fetchsitd(ehci, async);
+            itd_count++;
             break;
 
         case EST_ADVANCEQUEUE:
@@ -2079,7 +2082,8 @@ static void ehci_advance_state(EHCIState *ehci, int async)
             break;
         }
 
-        if (again < 0) {
+        if (again < 0 || itd_count > 16) {
+            /* TODO: notify guest (raise HSE irq?) */
             fprintf(stderr, "processing error - resetting ehci HC\n");
             ehci_reset(ehci);
             again = 0;