Change random number generator

Four fixes are applied in this patch:

  1) The `SYS_RandomInt()` function is renamed to `SYS_RandomLong()`,
  and its return type is now `long`. It no longer takes a range as
  parameters for its random number generation; it always uses the full
  range.
  2) The `getrandom()` syscall is added to configure.ac as a requested
  function.
  3) The generator for `SYS_RandomLong()` is changed. The previous
  generator was from the `rand()` function, but now it uses
  `getrandom()` when available and otherwise `lrand48()`, from the POSIX
  API.
  4) The seeding of the generator is via `SYS_InitRandom()`. It is
  modified accordingly to seed the new generator.

Addresses Ref #9
"Improve SYS_RandomInt()"
https://salsa.debian.org/rousseau/PCSC/-/issues/9

configure.ac

@@ -109,7 +109,7 @@ AC_STRUCT_DIRENT_D_TYPE
 AC_FUNC_ERROR_AT_LINE
 AC_FUNC_STAT
 AC_FUNC_VPRINTF
-AC_CHECK_FUNCS(getopt_long nanosleep strerror vsnprintf)
+AC_CHECK_FUNCS(getopt_long nanosleep strerror vsnprintf getrandom)
 AC_FUNC_ALLOCA
 
 # C Compiler features

src/readerfactory.c

@@ -1181,12 +1181,12 @@ SCARDHANDLE RFCreateReaderHandle(READER_CONTEXT * rContext)
  {
  READER_CONTEXT *dummy_reader;
 
- /* Create a random handle with 32 bits check to see if it already is
+ /* Create a random handle with 64 bits check to see if it already is
  * used. */
  /* FIXME: THIS IS NOT STRONG ENOUGH: A 128-bit token should be
  * generated. The client and server would associate token and hCard
  * for authentication. */
- randHandle = SYS_RandomInt(0, -1);
+ randHandle = SYS_RandomLong();
 
  /* do we already use this hCard somewhere? */
  ret = RFReaderInfoById(randHandle, &dummy_reader);

src/sys_generic.h

@@ -45,7 +45,7 @@ THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
  int SYS_USleep(int);
 
- int SYS_RandomInt(int, int);
+ long SYS_RandomLong(void);
 
  void SYS_InitRandom(void);
 

src/sys_unix.c

@@ -39,8 +39,12 @@ THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 #include "config.h"
 #include <sys/time.h>
+#include <limits.h>
 #include <stdlib.h>
 #include <time.h>
+#ifdef HAVE_GETRANDOM
+#include <sys/random.h>
+#endif /* HAVE_GETRANDOM */
 
 #include "misc.h"
 #include "sys_generic.h"
@@ -87,29 +91,42 @@ INTERNAL int SYS_USleep(int iTimeVal)
 /**
  * Generate a pseudo random number
  *
- * @param[in] fStart minimal value
- * @param[in] fEnd maximal value or -1 for a full range
+ * @return a non-negative random number
  *
- * @return a random number between fStart and fEnd
+ * @remark the range is at least up to `2^31`.
+ * @remark this is a CSPRNG when `getrandom()` is available, LCG otherwise.
+ * @warning SYS_InitRandom() should be called (once) before using this function.
+ * @warning not thread safe when system lacks `getrandom()` syscall.
+ * @warning not cryptographically secure when system lacks `getrandom()` syscall.
+ * @warning if interrupted by a signal, this function may return 0.
  */
-INTERNAL int SYS_RandomInt(int fStart, int fEnd)
+INTERNAL long SYS_RandomLong(void)
 {
- int iRandNum = 0;
-
- if (-1 == fEnd)
- /* full int range */
- iRandNum = rand();
- else
- iRandNum = ((rand()+0.0)/RAND_MAX * (fEnd - fStart)) + fStart;
-
- return iRandNum;
+#ifdef HAVE_GETRANDOM
+ unsigned long ul = 0;
+ unsigned char c[sizeof ul] = {0};
+ size_t i;
+
+ (void)getrandom(c, sizeof c, 0);
+ // this loop avoids trap representations that may occur in the naive solution
+ for(i = 0; i < sizeof ul; i++) {
+ ul <<= CHAR_BIT;
+ ul |= c[i];
+ }
+ // the casts are for the sake of clarity
+ return (long)(ul & (unsigned long)LONG_MAX);
+#else
+ long r = lrand48(); // this is not thread-safe
+ return r;
+#endif /* HAVE_GETRANDOM */
 }
 
 /**
  * Initialize the random generator
  */
 INTERNAL void SYS_InitRandom(void)
 {
+#ifndef HAVE_GETRANDOM
  struct timeval tv;
  struct timezone tz;
  long myseed = 0;
@@ -124,6 +141,7 @@ INTERNAL void SYS_InitRandom(void)
  myseed = (long) time(NULL);
  }
 
- srand(myseed);
+ srand48(myseed);
+#endif /* HAVE_GETRANDOM */
 }
 

src/winscard.c

@@ -210,7 +210,7 @@ LONG SCardEstablishContext(DWORD dwScope, /*@unused@*/ LPCVOID pvReserved1,
  * identified by clients and distinguished from others
  */
 
- *phContext = SYS_RandomInt(0, -1);
+ *phContext = SYS_RandomLong();
 
  Log2(PCSC_LOG_DEBUG, "Establishing Context: 0x%lX", *phContext);