Examples of errors detected by the V781 diagnostic

V781. Value of a variable is checked after it is used. Possible error in program's logic. Check lines: N1, N2.

FreeBSD Kernel

V781 The value of the 'lun' variable is checked after it was used. Perhaps there is a mistake in program logic. Check lines: 1617, 1619. sbp_targ.c 1617

static void
sbp_targ_mgm_handler(struct fw_xfer *xfer)
{
  ....
  int exclusive = 0, lun;
  ....
  lun = orb4->id;
  lstate = orbi->sc->lstate[lun];

  if (lun >= MAX_LUN || lstate == NULL ||
      (exclusive &&
      STAILQ_FIRST(&lstate->logins) != NULL &&
      STAILQ_FIRST(&lstate->logins)->fwdev != orbi->fwdev)
     ) {
    /* error */
    orbi->status.dead = 1;
    orbi->status.status = STATUS_ACCESS_DENY;
    orbi->status.len = 1;
    break;
  }
  ....
}

XNU kernel

V781 CWE-129 The value of the 'channel_index' variable is checked after it was used. Perhaps there is a mistake in program logic. Check lines: 852, 855. IOStateReporter.cpp 852

IOReturn
IOStateReporter::updateChannelValues(int channel_index)
{
  ....
  state_index = _currentStates[channel_index];

  if (channel_index < 0 ||
      channel_index > (_nElements - state_index)
                        / _channelDimension) {
    result = kIOReturnOverrun; goto finish;
  }
  ....
}

It is very suspicious that the variable channel_index is used as an array index. And only after that a check occurs, that the variable does not exceed certain limits values.

Similar errors can be found in some other places:

• V781 CWE-129 The value of the 'channel_index' variable is checked after it was used. Perhaps there is a mistake in program logic. Check lines: 651, 654. IOStateReporter.cpp 651
• V781 CWE-129 The value of the 'pri' variable is checked after it was used. Perhaps there is a mistake in program logic. Check lines: 267, 269. pktsched_fq_codel.c 267
• V781 CWE-129 The value of the 'pcid' variable is checked after it was used. Perhaps there is a mistake in program logic. Check lines: 224, 225. pmap_pcid.c 224

System Shock

V781 The value of the 'num_args' variable is checked after it was used. Perhaps there is a mistake in program logic. Check lines: 224, 225. FIX24TST.C 224

#define MAX_ARGS 8
....
bool args_neg[MAX_ARGS];
....
void parse (char *str, bool command)
{
  ....
  args_neg[num_args] = neg = FALSE;
  if (num_args == MAX_ARGS) break;
  ....
}

System Shock

V781 The value of the 'model_num' variable is checked after it was used. Perhaps there is a mistake in program logic. Check lines: 567, 569. RENDTOOL.C 567

uchar model_base_nums[MAX_VTEXT_OBJS];
....
void load_model_vtexts(char model_num)
{
  short curr = model_base_nums[model_num];
  ....
  if (model_num >= MAX_VTEXT_OBJS)
    return;
}

Qt

V781 CWE-129 The value of the 'signal' variable is checked after it was used. Perhaps there is a mistake in program logic. Check lines: 397, 413. qobject.cpp 397

void QObjectPrivate::addConnection(int signal, Connection *c)
{
  ....
  if (signal >= connectionLists->count())
    connectionLists->resize(signal + 1);

  ConnectionList &connectionList = (*connectionLists)[signal];
  ....
  if (signal < 0) {
  ....
}

Haiku Operation System

V781 The value of the 'vector' variable is checked after it was used. Perhaps there is a mistake in program logic. Check lines: 802, 805. oce_if.c 802

#define OCE_MAX_EQ 32

typedef struct oce_softc {
  ....
  OCE_INTR_INFO intrs[OCE_MAX_EQ];
  ....
} OCE_SOFTC, *POCE_SOFTC;

static int
oce_alloc_intr(POCE_SOFTC sc, int vector, void (*isr) (void *arg, int pending))
{
  POCE_INTR_INFO ii = &sc->intrs[vector];
  int rc = 0, rr;

  if (vector >= OCE_MAX_EQ)
    return (EINVAL);
  ....
}

GCC

V781 The value of the 'best_alg->ops' variable is checked after it was used. Perhaps there is a mistake in program logic. Check lines: 3157, 3164. expmed.c 3157

struct algorithm
{
  struct mult_cost cost;
  short ops;
  enum alg_code op[MAX_BITS_PER_WORD];
  char log[MAX_BITS_PER_WORD];
};

static void
synth_mult (struct algorithm *alg_out, unsigned HOST_WIDE_INT t,
            const struct mult_cost *cost_limit, machine_mode mode)
{
  int m;
  struct algorithm *alg_in, *best_alg;
  ....
  /* Cache the result.  */
  if (!cache_hit)
    {
      entry_ptr->t = t;
      entry_ptr->mode = mode;
      entry_ptr->speed = speed;
      entry_ptr->alg = best_alg->op[best_alg->ops];
      entry_ptr->cost.cost = best_cost.cost;
      entry_ptr->cost.latency = best_cost.latency;
    }

  /* If we are getting a too long sequence for `struct algorithm'
     to record, make this search fail.  */
  if (best_alg->ops == MAX_BITS_PER_WORD)
    return;
  ....
}

Minetest

V781 The value of the 'i' index is checked after it was used. Perhaps there is a mistake in program logic. irrString.h 572

bool equalsn(const string<T,TAlloc>& other, u32 n) const
{
  u32 i;
  for(i=0; array[i] && other[i] && i < n; ++i) // <=
    if (array[i] != other[i])
      return false;

  // if one (or both) of the strings was smaller then they
  // are only equal if they have the same length
  return (i == n) || (used == other.used);
}

Qemu

V781 The value of the 'ix' index is checked after it was used. Perhaps there is a mistake in program logic. uri.c 2110

char *uri_resolve_relative(const char *uri, const char *base)
{
  ....
  ix = pos;
  if ((ref->path[ix] == '/') && (ix > 0)) {
  ....
}

GTK

V781 [CWE-129] The value of the 'idx' variable is checked after it was used. Perhaps there is a mistake in program logic. Check lines: 71, 73. gtkatspiaction.c 71

static void
action_handle_method (GtkAtSpiContext        *self,
                      const char             *method_name,
                      GVariant               *parameters,
                      GDBusMethodInvocation  *invocation,
                      const Action           *actions,
                      int                     n_actions)
{
  ....
  int idx = -1;

  g_variant_get (parameters, "(i)", &idx);

  const Action *action = &actions[idx];

  if (idx >= 0 && idx < n_actions)
    g_dbus_method_invocation_return_value (
      invocation, g_variant_new ("(s)", action->name));
  else
    g_dbus_method_invocation_return_error (invocation,
                                           G_IO_ERROR,
                                           G_IO_ERROR_INVALID_ARGUMENT,
                                           "Unknown action %d",
                                           idx);
  ....
}

Similar errors can be found in some other places:

• V781 [CWE-129] The value of the 'idx' variable is checked after it was used. Perhaps there is a mistake in program logic. Check lines: 132, 134. gtkatspiaction.c 132

libtorrent

V781 The value of the 'read_pos' index is checked after it was used. Perhaps there is a mistake in program logic. http_stream.hpp:166.

template <typename Handler>
void handshake2(error_code const& e, Handler h)
{
  ....
  std::size_t const read_pos = m_buffer.size();
  ....
  if (m_buffer[read_pos - 1] == '\n' && read_pos > 2) // <=
  {
    if (m_buffer[read_pos - 2] == '\n')
    {
      found_end = true;
    }
    else if (read_pos > 4
      && m_buffer[read_pos - 2] == '\r'
      && m_buffer[read_pos - 3] == '\n'
      && m_buffer[read_pos - 4] == '\r')
    {
      found_end = true;
    }
  }
  ....
}

TheXTech

V781 The value of the 'whatPlayer' index is checked after it was used. Perhaps there is a mistake in program logic. thextech blocks.cpp 159

if(b.ShakeY != 0 || b.ShakeY2 != 0 || b.ShakeY3 != 0)
{
  if(  b.RapidHit > 0
    && Player[whatPlayer].Character == 4 && whatPlayer > 0) // <=
  {
    b.RapidHit = (iRand() % 3) + 1;
  }
  return;
}

LLVM/Clang

V781 [CWE-20, CERT-API00-C] The value of the 'sourceDim' index is checked after it was used. Perhaps there is a mistake in program logic. ReshapeOpsUtils.cpp 49

Optional<SmallVector<ReassociationIndices>>
mlir::getReassociationIndicesForCollapse(ArrayRef<int64_t> sourceShape,
                                         ArrayRef<int64_t> targetShape) {
  unsigned sourceDim = 0;
  ....
  int64_t currTargetShape = targetShape[targetDim];
  while (sourceShape[sourceDim] != ShapedType::kDynamicSize &&
         prodOfCollapsedDims * sourceShape[sourceDim] < currTargetShape &&
         sourceDim < sourceShape.size()) {
    prodOfCollapsedDims *= sourceShape[sourceDim];
    currIndices.push_back(sourceDim++);
  }
  ....
}

Captain Blood

V781 [CWE-20, CERT-API00-C] The value of the 'start' index is checked after it was used. Perhaps there is a mistake in program logic. coreloader.h 136

__forceinline void GetBootParams(const char * bootIni)
{
  long start = 0;
  // ....
  if (bootIni[start] && start > 0)
  {
    // ....
  }
  // ....
}

GZDoom

V781 The value of the 'len' index is checked after it was used. Perhaps there is a mistake in program logic. s_reverbedit.cpp 193

FString SuggestNewName(const ReverbContainer *env)
{
  char text[32];
  size_t len;

  strncpy(text, env->Name, 31);
  text[31] = 0;

  len = strlen(text);
  ....
  if (text[len - 1] != ' ' && len < 31)      // <=
  {
    text[len++] = ' ';
  }
}