sched/signal: add sanity check for siginfo

add sanity check for siginfo to ensure whether there is really a
consumer waiting for the signal, since the task state will not be
changed appropriately if in cancel/killed case

Test Case:
https://github.com/linux-test-project/ltp/blob/master/testcases/open_posix_testsuite/conformance/interfaces/sigpause/1-1.c#L63

Signed-off-by: chao an <anchao@lixiang.com>

sched/signal/sig_dispatch.c

@@ -397,8 +397,12 @@ int nxsig_tcbdispatch(FAR struct tcb_s *stcb, siginfo_t *info)
       if (stcb->task_state == TSTATE_WAIT_SIG &&
           (masked == 0 ||
            nxsig_ismember(&stcb->sigwaitmask, info->si_signo)))
+        {
+          if (stcb->sigunbinfo != NULL)
             {
               memcpy(stcb->sigunbinfo, info, sizeof(siginfo_t));
+            }
+
           sigemptyset(&stcb->sigwaitmask);
 
           if (WDOG_ISACTIVE(&stcb->waitdog))
@@ -460,8 +464,12 @@ int nxsig_tcbdispatch(FAR struct tcb_s *stcb, siginfo_t *info)
        */
 
       if (stcb->task_state == TSTATE_WAIT_SIG)
+        {
+          if (stcb->sigunbinfo != NULL)
             {
               memcpy(stcb->sigunbinfo, info, sizeof(siginfo_t));
+            }
+
           sigemptyset(&stcb->sigwaitmask);
 
           if (WDOG_ISACTIVE(&stcb->waitdog))

sched/signal/sig_timedwait.c

@@ -99,6 +99,8 @@ static void nxsig_timeout(wdparm_t arg)
     {
       FAR struct tcb_s *rtcb = this_task();
 
+      if (wtcb->sigunbinfo != NULL)
+        {
           wtcb->sigunbinfo->si_signo           = SIG_WAIT_TIMEOUT;
           wtcb->sigunbinfo->si_code            = SI_TIMER;
           wtcb->sigunbinfo->si_errno           = ETIMEDOUT;
@@ -107,6 +109,7 @@ static void nxsig_timeout(wdparm_t arg)
           wtcb->sigunbinfo->si_pid             = 0;  /* Not applicable */
           wtcb->sigunbinfo->si_status          = OK;
 #endif
+        }
 
       /* Remove the task from waitting list */
 
@@ -166,6 +169,8 @@ void nxsig_wait_irq(FAR struct tcb_s *wtcb, int errcode)
     {
       FAR struct tcb_s *rtcb = this_task();
 
+      if (wtcb->sigunbinfo != NULL)
+        {
           wtcb->sigunbinfo->si_signo           = SIG_CANCEL_TIMEOUT;
           wtcb->sigunbinfo->si_code            = SI_USER;
           wtcb->sigunbinfo->si_errno           = errcode;
@@ -174,6 +179,7 @@ void nxsig_wait_irq(FAR struct tcb_s *wtcb, int errcode)
           wtcb->sigunbinfo->si_pid             = 0;  /* Not applicable */
           wtcb->sigunbinfo->si_status          = OK;
 #endif
+        }
 
       /* Remove the task from waitting list */
 
@@ -376,6 +382,8 @@ int nxsig_timedwait(FAR const sigset_t *set, FAR struct siginfo *info,
             }
           else
             {
+              rtcb->sigunbinfo = NULL;
+
               leave_critical_section(flags);
               return -EAGAIN;
             }