SCardListReaders: Conditional jump or move depends on uninitialised value(s)

Ludovic Rousseau ludovic.rousseau at
Wed May 11 12:42:59 CEST 2022


I hope it is the correct way to report bugs and patches.

GnuPG is not using the PC/SC API correctly. With the function
SCardListReaders() the last parameter (size of the readers buffer) is a
in/out parameter. i.e. the value MUST be initialized before calling.

According to the API documentation

LONG SCardListReaders     (     SCARDCONTEXT      hContext,
         LPCSTR      mszGroups,
         LPSTR      mszReaders,
         LPDWORD      pcchReaders

If *pcchReaders is equal to SCARD_AUTOALLOCATE then the function will
allocate itself the needed memory. Use SCardFreeMemory() to release it.

In the GnuPG code the value of pcchReaders is not initialized and that
generates a log reported by valgrind:
==35605== Thread 2:
==35605== Conditional jump or move depends on uninitialised value(s)
==35605==    at 0x58BCFAE: SCardListReaders (in /usr/lib64/
==35605==    by 0x11D78A: apdu_dev_list_start (apdu.c:2031)
==35605==    by 0x1245EF: select_application (app.c:817)
==35605==    by 0x117AFF: open_card_with_request (command.c:281)
==35605==    by 0x117AFF: cmd_serialno (command.c:358)
==35605==    by 0x4A20839: ??? (in /usr/lib64/
==35605==    by 0x4A20C28: assuan_process (in /usr/lib64/
==35605==    by 0x11854C: scd_command_handler (command.c:2521)
==35605==    by 0x114C03: start_connection_thread (scdaemon.c:1202)
==35605==    by 0x4A2F49D: ??? (in /usr/lib64/
==35605==    by 0x4ABD3E9: start_thread (pthread_create.c:442)
==35605==    by 0x4B3F0DF: clone (clone.S:100)

The patch is very simple:
diff --git a/scd/apdu.c b/scd/apdu.c
index 574697cc1..e83815ba5 100644
--- a/scd/apdu.c
+++ b/scd/apdu.c
@@ -2015,7 +2015,7 @@ apdu_dev_list_start (const char *portstr, struct dev_list **l_p)
      { /* PC/SC readers.  */
        long r;
-      pcsc_dword_t nreader;
+      pcsc_dword_t nreader = 0;
        char *p = NULL;

        if (!pcsc.context)

I found the problem because of and


Dr. Ludovic Rousseau

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