[PATCH v1] ShellPkg: Fix 'ping' command Ip4 receive flow.

["Maciej Rabeda" <maciej.rabeda@linux.intel.com>]

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=2032

'ping' command's receive flow utilizes a single Rx token which it
attempts to reuse before recycling the previously received packet.
This causes a situation where under ICMP traffic,
Ping6OnEchoReplyReceived() function will receive an already
recycled packet with EFI_SUCCESS token status and finally
dereference invalid pointers from RxData structure.

Cc: Ray Ni <ray.ni@intel.com>
Cc: Zhichao Gao <zhichao.gao@intel.com>
Signed-off-by: Maciej Rabeda <maciej.rabeda@linux.intel.com>
---
 ShellPkg/Library/UefiShellNetwork1CommandsLib/Ping.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/ShellPkg/Library/UefiShellNetwork1CommandsLib/Ping.c b/ShellPkg/Library/UefiShellNetwork1CommandsLib/Ping.c
index 23567fa2c1bb..a3fa32515192 100644
--- a/ShellPkg/Library/UefiShellNetwork1CommandsLib/Ping.c
+++ b/ShellPkg/Library/UefiShellNetwork1CommandsLib/Ping.c
@@ -614,6 +614,11 @@ Ping6OnEchoReplyReceived (
 
 ON_EXIT:
 
+  //
+  // Recycle the packet before reusing RxToken
+  //
+  gBS->SignalEvent (Private->IpChoice == PING_IP_CHOICE_IP6?((EFI_IP6_RECEIVE_DATA*)Private->RxToken.Packet.RxData)->RecycleSignal:((EFI_IP4_RECEIVE_DATA*)Private->RxToken.Packet.RxData)->RecycleSignal);
+
   if (Private->RxCount < Private->SendNum) {
     //
     // Continue to receive icmp echo reply packets.
@@ -632,10 +637,6 @@ ON_EXIT:
     //
     Private->Status = EFI_SUCCESS;
   }
-  //
-  // Singal to recycle the each rxdata here, not at the end of process.
-  //
-  gBS->SignalEvent (Private->IpChoice == PING_IP_CHOICE_IP6?((EFI_IP6_RECEIVE_DATA*)Private->RxToken.Packet.RxData)->RecycleSignal:((EFI_IP4_RECEIVE_DATA*)Private->RxToken.Packet.RxData)->RecycleSignal);
 }
 
 /**
-- 
2.24.0.windows.2