Mitigated race condition of SYSTEM,EXEC child processes

CHANGES

@@ -18,6 +18,9 @@ Corrections:
 	building failed on Solaris 9.
 	Thanks to Greg Earle for reporting this issue and providing a patch.
 
+	Mitigated race condition of quickly terminating SYSTEM or EXEC child
+	processes.
+
 Porting:
 	In gcc version 10 the default changed from -fcommon to -fno-common.
 	Consequently, linking filan and procan failed with error

socat.c

@@ -597,29 +597,20 @@ int socat(const char *address1, const char *address2) {
        (XIO_RDSTREAM(sock1)->howtoend == END_KILL ||
 	XIO_RDSTREAM(sock1)->howtoend == END_CLOSE_KILL ||
 	XIO_RDSTREAM(sock1)->howtoend == END_SHUTDOWN_KILL)) {
-      if (XIO_RDSTREAM(sock1)->para.exec.pid == diedunknown1) {
+      int i;
+      for (i = 0; i < NUMUNKNOWN; ++i) {
+	 if (XIO_RDSTREAM(sock1)->para.exec.pid == diedunknown[i]) {
 	    /* child has alread died... but it might have put regular data into
 	       the communication channel, so continue */
-	 Info1("child "F_pid" has already died (diedunknown1)",
+	    Info2("child "F_pid" has already died with status %d",
-	       XIO_RDSTREAM(sock1)->para.exec.pid);
+		  XIO_RDSTREAM(sock1)->para.exec.pid, statunknown[i]);
-	 diedunknown1 = 0;
+	    if (statunknown[i] != 0) {
+	       return 1;
+	    }
+	    diedunknown[i] = 0;
 	    XIO_RDSTREAM(sock1)->para.exec.pid = 0;
 	    /* return STAT_RETRYLATER; */
-      } else if (XIO_RDSTREAM(sock1)->para.exec.pid == diedunknown2) {
+	 }
-	 Info1("child "F_pid" has already died (diedunknown2)",
-	       XIO_RDSTREAM(sock1)->para.exec.pid);
-	 diedunknown2 = 0;
-	 XIO_RDSTREAM(sock1)->para.exec.pid = 0;
-      } else if (XIO_RDSTREAM(sock1)->para.exec.pid == diedunknown3) {
-	 Info1("child "F_pid" has already died (diedunknown3)",
-	       XIO_RDSTREAM(sock1)->para.exec.pid);
-	 diedunknown3 = 0;
-	 XIO_RDSTREAM(sock1)->para.exec.pid = 0;
-      } else if (XIO_RDSTREAM(sock1)->para.exec.pid == diedunknown4) {
-	 Info1("child "F_pid" has already died (diedunknown4)",
-	       XIO_RDSTREAM(sock1)->para.exec.pid);
-	 diedunknown4 = 0;
-	 XIO_RDSTREAM(sock1)->para.exec.pid = 0;
       }
    }
 #endif
@@ -648,29 +639,20 @@ int socat(const char *address1, const char *address2) {
        (XIO_RDSTREAM(sock2)->howtoend == END_KILL ||
 	XIO_RDSTREAM(sock2)->howtoend == END_CLOSE_KILL ||
 	XIO_RDSTREAM(sock2)->howtoend == END_SHUTDOWN_KILL)) {
-      if (XIO_RDSTREAM(sock2)->para.exec.pid == diedunknown1) {
+      int i;
+      for (i = 0; i < NUMUNKNOWN; ++i) {
+	 if (XIO_RDSTREAM(sock2)->para.exec.pid == diedunknown[i]) {
 	    /* child has alread died... but it might have put regular data into
 	       the communication channel, so continue */
-	 Info1("child "F_pid" has already died (diedunknown1)",
+	    Info2("child "F_pid" has already died with status %d",
-	       XIO_RDSTREAM(sock2)->para.exec.pid);
+		  XIO_RDSTREAM(sock2)->para.exec.pid, statunknown[i]);
-	 diedunknown1 = 0;
+	    if (statunknown[i] != 0) {
+	       return 1;
+	    }
+	    diedunknown[i] = 0;
 	    XIO_RDSTREAM(sock2)->para.exec.pid = 0;
 	    /* return STAT_RETRYLATER; */
-      } else if (XIO_RDSTREAM(sock2)->para.exec.pid == diedunknown2) {
+	 }
-	 Info1("child "F_pid" has already died (diedunknown2)",
-	       XIO_RDSTREAM(sock2)->para.exec.pid);
-	 diedunknown2 = 0;
-	 XIO_RDSTREAM(sock2)->para.exec.pid = 0;
-      } else if (XIO_RDSTREAM(sock2)->para.exec.pid == diedunknown3) {
-	 Info1("child "F_pid" has already died (diedunknown3)",
-	       XIO_RDSTREAM(sock2)->para.exec.pid);
-	 diedunknown3 = 0;
-	 XIO_RDSTREAM(sock2)->para.exec.pid = 0;
-      } else if (XIO_RDSTREAM(sock2)->para.exec.pid == diedunknown4) {
-	 Info1("child "F_pid" has already died (diedunknown4)",
-	       XIO_RDSTREAM(sock2)->para.exec.pid);
-	 diedunknown4 = 0;
-	 XIO_RDSTREAM(sock2)->para.exec.pid = 0;
       }
    }
 #endif

test.sh

@@ -8520,16 +8520,17 @@ esac
 N=$((N+1))
 
 
-# test the shut-null and null-eof options
+# Test the shut-null and null-eof options
 NAME=SHUTNULLEOF
 case "$TESTS" in
 *%$N%*|*%functions%*|*%socket%*|*%$NAME%*)
 TEST="$NAME: options shut-null and null-eof"
-# run a receiving background process with option null-eof. 
+# Run a receiving background process with option null-eof. 
-# start a sending process with option shut-null that sends a test record to the
+# Start a sending process with option shut-null that sends a test record to the
 # receiving process and then terminates.
-# send another test record.
+# Send another test record.
-# whe the receiving process just got the first test record the test succeeded
+# When the receiving process only received and stored the first test record the
+# test succeeded
 if ! eval $NUMCOND; then :; else
 tf="$td/test$N.stout"
 te="$td/test$N.stderr"
@@ -8541,9 +8542,9 @@ printf "test $F_n $TEST... " $N
 $CMD0 >/dev/null 2>"${te}0" &
 pid0=$!
 waitudp4port $PORT 1
-echo "$da" |$CMD1 >"${tf}1" 2>"${te}1"
+{ echo "$da"; sleep 0.1; } |$CMD1 >"${tf}1" 2>"${te}1"
 rc1=$?
-echo "xyz" |$CMD1 >"${tf}2" 2>"${te}2"
+{ echo "xyz"; sleep 0.1; } |$CMD1 >"${tf}2" 2>"${te}2"
 rc2=$?
 kill $pid0 2>/dev/null; wait
 if [ $rc1 != 0 -o $rc2 != 0 ]; then
@@ -12161,7 +12162,7 @@ case "$TESTS" in
 TEST="$NAME: correct evaluation of range mask 0"
 if ! eval $NUMCOND; then :;
 elif [ -z "$SECONDADDR" ]; then
-    # we need access to a second addresses
+    # we need access to a second address
     $PRINTF "test $F_n $TEST... ${YELLOW}need a second IPv4 address${NORMAL}\n" $N
     numCANT=$((numCANT+1))
     listCANT="$listCANT $N"
@@ -12179,6 +12180,7 @@ pid0=$!
 waittcp4port $PORT 1
 echo "$da" |$CMD1 >"${tf}1" 2>"${te}1"
 rc1=$?
+sleep 1
 kill $pid0 2>/dev/null; wait
 if [ $rc1 != 0 ]; then
     $PRINTF "${YELLOW}invocation failed${NORMAL}\n"

xio.h

@@ -416,6 +416,7 @@ extern pid_t diedunknown[NUMUNKNOWN];	/* child died before it is registered */
 #define diedunknown2 (diedunknown[1])
 #define diedunknown3 (diedunknown[2])
 #define diedunknown4 (diedunknown[3])
+extern int   statunknown[NUMUNKNOWN]; 	/* exit state of unknown dead child */
 
 extern int xiosetsigchild(xiofile_t *xfd, int (*callback)(struct single *));
 extern int xiosetchilddied(void);

xiosigchld.c

@@ -11,6 +11,7 @@
 
 /*!! with socat, at most 4 exec children exist */
 pid_t diedunknown[NUMUNKNOWN];	/* children that died before they were registered */
+int   statunknown[NUMUNKNOWN]; 	/* exit state of unknown dead child */
 size_t nextunknown;
 
 
@@ -120,7 +121,8 @@ void childdied(int signum) {
 	 if (nextunknown == NUMUNKNOWN) {
 	    nextunknown = 0;
 	 }
-	 diedunknown[nextunknown++] = pid;
+	 diedunknown[nextunknown] = pid;
+	 statunknown[nextunknown++] = WEXITSTATUS(status);
 	 Debug1("saving pid in diedunknown"F_Zu,
 		nextunknown/*sic, for compatibility*/);
       }