From 192113552faa98f40cc91fe014ec55861474626c Mon Sep 17 00:00:00 2001
From: Werner Koch <wk@gnupg.org>
Date: Tue, 7 Sep 2021 16:40:09 +0200
Subject: [PATCH] scd: Fix possible assertion in close_pcsc_reader.

* scd/apdu.c (close_pcsc_reader): Don't ref-count if the context is
invalid.
(open_pcsc_reader): Compare the context against -1 which is our
indicator for an invalid context.
--

I got a crash report for Windows:

  DBG: chan_0x000000a4 <- RESTART
  DBG: chan_0x000000a4 -> OK
  DBG: chan_0x000000a4 <- SERIALNO
  DBG: open_pcsc_reader(portstr=(null))
  reader slot 0: not connected
  DBG: open_pcsc_reader => slot=0
  DBG: enter: apdu_connect: slot=0
  pcsc_connect failed: invalid PC/SC error code (0x6)
  reader slot 0: not connected
  DBG: leave: apdu_connect => sw=0x1000b
  DBG: enter: apdu_close_reader: slot=0
  DBG: enter: apdu_disconnect: slot=0
  DBG: leave: apdu_disconnect => sw=0x0
  Ohhhh jeeee: Assertion "pcsc.count > 0" in
    close_pcsc_reader failed (...2.2.28/scd/apdu.c:817)

no smartcard reader was connected but the box might sport a virtual
reader.  This patch should make it more robust.

Signed-off-by: Werner Koch <wk@gnupg.org>
---
 scd/apdu.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/scd/apdu.c b/scd/apdu.c
index a42808c75..f00b35915 100644
--- a/scd/apdu.c
+++ b/scd/apdu.c
@@ -90,7 +90,7 @@ typedef unsigned long pcsc_dword_t;
 
 /* PC/SC context to access readers.  Shared among all readers.  */
 static struct pcsc {
-  int count;
+  int count;     /* Reference count - valid if .context != -1 */
   long context;
 } pcsc;
 
@@ -814,11 +814,17 @@ static int
 close_pcsc_reader (int slot)
 {
   (void)slot;
-  log_assert (pcsc.count > 0);
-  if (--pcsc.count == 0)
+
+  /* Note that we might be called via apdu_close_reader and we can't
+   * guarantee that we have not yet been called.  */
+  if (pcsc.context != -1)
     {
-      pcsc_release_context (pcsc.context);
-      pcsc.context = -1;
+      log_assert (pcsc.count > 0);
+      if (--pcsc.count == 0)
+        {
+          pcsc_release_context (pcsc.context);
+          pcsc.context = -1;
+        }
     }
   return 0;
 }
@@ -1199,7 +1205,7 @@ open_pcsc_reader (const char *portstr)
   char *p;
   size_t n;
 
-  if (pcsc.context < 0)
+  if (pcsc.context == -1)
     if (pcsc_init () < 0)
       return -1;