From: Prasad J Pandit <pjp@fedoraproject.org>
Date: Thu, 22 Sep 2016 16:02:37 +0530
Subject: [PATCH] net: mcf: limit buffer descriptor count

ColdFire Fast Ethernet Controller uses buffer descriptors to manage
data flow to/fro receive & transmit queues. While transmitting
packets, it could continue to read buffer descriptors if a buffer
descriptor has length of zero and has crafted values in bd.flags.
Set upper limit to number of buffer descriptors.

Reported-by: Li Qiang <liqiang6-s@360.cn>
Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
(cherry picked from commit 070c4b92b8cd5390889716677a0b92444d6e087a)
---
 hw/net/mcf_fec.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/hw/net/mcf_fec.c b/hw/net/mcf_fec.c
index 0ee8ad9..d31fea1 100644
--- a/hw/net/mcf_fec.c
+++ b/hw/net/mcf_fec.c
@@ -23,6 +23,7 @@ do { printf("mcf_fec: " fmt , ## __VA_ARGS__); } while (0)
 #define DPRINTF(fmt, ...) do {} while(0)
 #endif
 
+#define FEC_MAX_DESC 1024
 #define FEC_MAX_FRAME_SIZE 2032
 
 typedef struct {
@@ -149,7 +150,7 @@ static void mcf_fec_do_tx(mcf_fec_state *s)
     uint32_t addr;
     mcf_fec_bd bd;
     int frame_size;
-    int len;
+    int len, descnt = 0;
     uint8_t frame[FEC_MAX_FRAME_SIZE];
     uint8_t *ptr;
 
@@ -157,7 +158,7 @@ static void mcf_fec_do_tx(mcf_fec_state *s)
     ptr = frame;
     frame_size = 0;
     addr = s->tx_descriptor;
-    while (1) {
+    while (descnt++ < FEC_MAX_DESC) {
         mcf_fec_read_bd(&bd, addr);
         DPRINTF("tx_bd %x flags %04x len %d data %08x\n",
                 addr, bd.flags, bd.length, bd.data);