SFTP receives SIGTERM and SIGCHLD signals at the same time, which may kill almost all processes of the linux system（kill SIGTERM -1）.

1、A process sends SIGTERM to sftp
2、sigchld_handler is running，after executing "if (sshpid > 1)", sftp receive SIGCHLD 

static void killchild(int signo)
{
	if (sshpid > 1) {
                                         <-------- Receive SIGCHLD signal
		kill(sshpid, SIGTERM);
		(void) waitpid(sshpid, NULL, 0);
	}

	_exit(1);
}

3、subprocess（ssh） connection closed，it send SIGCHLD  to sftp
4、sigchld_handler start execution on the same cpu，so sshpid =-1

static void sigchld_handler(int sig)
{
 .......
		(void)write(STDERR_FILENO, msg, sizeof(msg) - 1);
		sshpid = -1;	<----
}

5、killchild continue to finish，and exec "kill(-1, SIGTERM);"


I think add a patch

diff --git a/sftp.c b/sftp.c
index b66037f..833e034 100644
--- a/sftp.c
+++ b/sftp.c
@@ -2297,6 +2297,7 @@ static void
 connect_to_server(char *path, char **args, int *in, int *out)
 {
        int c_in, c_out;
+    struct sigaction kact,sact;

 #ifdef USE_PIPES
        int pin[2], pout[2];
@@ -2343,12 +2344,21 @@ connect_to_server(char *path, char **args, int *in, int *out)
                _exit(1);
        }

-       signal(SIGTERM, killchild);
-       signal(SIGINT, killchild);
-       signal(SIGHUP, killchild);
-       signal(SIGTSTP, suspchild);
-       signal(SIGTTIN, suspchild);
-       signal(SIGTTOU, suspchild);
+    kact.sa_handler = killchild;
+    sigemptyset(&kact.sa_mask);
+    sigaddset(&kact.sa_mask, SIGCHLD);
+    sigaction(SIGTERM, &kact, NULL);
+    sigaction(SIGINT, &kact, NULL);
+    sigaction(SIGHUP, &kact, NULL);
+
+    sact.sa_handler = suspchild;
+    sigemptyset(&sact.sa_mask);
+    sigaddset(&sact.sa_mask, SIGCHLD);
+    sigaction(SIGTSTP, suspchild);
+    sigaction(SIGTTIN, suspchild);
+    sigaction(SIGTTOU, suspchild);
+
+
        signal(SIGCHLD, sigchld_handler);
        close(c_in);
        close(c_out);